Iplo Ma in Rew

Module 1

REWING B

1.1 Brewing Raw Materials

1.1.2 Adjuncts 1.1.3 Water 1.1.4 Hops IPLOMA IN

Contents

Abstract ...... 1 Learning Outcomes ...... 1 Prerequisite Understanding ...... 1 1.1.2 Adjuncts ...... 2 Introduction ...... 2 Solid Adjuncts ...... 2 Liquid Adjuncts ...... 3 Use of Adjuncts in the Brewery ...... 7 Adjunct Starch and Gelatinisation Temperature ...... 9 Commercial Enzymes in Brewing ...... 10 Speciality Malts ...... 13 Self-Assessment Questions ...... 18 Self Assessment Answers ...... 19 1.1.3 Water ...... 21 Introduction ...... 21 Water Hardness ...... 24 Measuring Water Hardness ...... 25 Brewing Water Ionic Content ...... 25 Microbiological Treatments ...... 27 Self-Assessment Questions ...... 31 Self-Assessment Answers ...... 32 1.1.4 Hops ...... 33 Introduction ...... 33 Hop Cultivation ...... 35 Chemical Composition of Hop Constituents ...... 38 Processed Hop Products ...... 42 The Use of Hops in Brewing ...... 48 Self-Assessment Questions ...... 53 Self-Assessment Answers ...... 55

ABSTRACT

In this continuation of Module 1.1 (Brewing Raw Materials) of the Diploma in Brewing, we will examine the non-malted raw materials used in wort production (yeast and fermentation is covered in Module 2). These are: Adjuncts, Water and Hops.

Firstly, we will consider the range of brewing adjuncts available, including their uses, composition and methods of manufacture. Typical specifications and relevance to brewing performance will be discussed.

Secondly, the impact of water composition and quality on beer processing and quality will be examined. This will include typical specifications and methods of analysis for brewing water, and their relevance for predicting wort composition, extract efficiency and brewing performance.

Finally, we will look at hops, and consider hop selection, hop constituents, available hop products and their use throughout the brewing process.

LEARNING OUTCOMES

On completion of this section you should be able to:

1. Understand the range of brewing adjuncts and specialty malts and their use in the brewery.

2. Describe a specification for brewing water treatment and understand the impact of water on wort production and beer quality.

3. Understand the selection of hops and hop products for use throughout the brewing process.

PREREQUISITE UNDERSTANDING

Basic scientific knowledge and terminology.

With reduced protein levels, the proportions 1.1.2 ADJUNCTS of malt and adjuncts in the grist can be varied, to adjust beer characteristics. For example, Introduction extra flavour and colour can be introduced without compounding excessive protein levels There are a variety of different adjuncts from malt. available to the brewer. Such adjuncts can be categorised and subdivided as follows: Lipid levels are slightly raised when using torrified adjuncts in comparison to others, but Solid Adjuncts Liquid Adjuncts this can be negated in the final wort by increasing the total proportion of adjuncts in Roasted Glucose Syrups the grist. There is no handling or dust Torrified Sucrose Syrups problems associated with torrified products Micronised Invert Sugars and they can be added to the usual grist bill Flaked Malt Extracts for normal milling and mashing. However, higher extract yields prevail if micronised and Grits Caramel torrified products are first pre-cooked, but Flours Primings this is at the expense of additional processing costs.

Solid Adjuncts Flaked Flaking of cereals to produce adjuncts is Roasted typically, a two-stage process. Firstly, the Barley predominates as the main roasted cereal is partially gelatinised either through adjunct and is used as a cheaper alternative to mild pressure-cooking or by steaming at speciality chocolate malts. The unmalted atmospheric pressure. Secondly, the semi- grain is roasted in a heated rotating drum, processed cereal grits are passed through producing a “concentrated” grain that imparts rollers held at approximately 85°C, before the more colour and flavour. Roasted and raw moisture content of the flake is reduced to 8- barley used as adjuncts, cause processing 10%. Flaked adjuncts, as with the torrified problems due to the structural integrity of and micronised adjuncts can be added directly their grains. Unmalted barley is an extremely to the grist bill and processed throughout the abrasive grain, rapidly eroding the rollers of brewhouse without any special requirements, the mill, leading to increased maintenance depending on the cereal variety. For example, and repair outlays. flaked barley does not need pre-cooking but flaked maize and rice, which have higher gelatinisation temperatures will. Torrified / Micronised In this process, cereals are subjected to heat at 260°C in the form of either hot sand or air Grits (torrification) or, infrared heat Grits of various adjuncts are prepared through (micronisation). The heat rapidly increases coarse milling. The milling process removes the internal water vapour causing the grain to the husk and outer layers of the endosperm expand until it pops. This heat partly cooks along with the oil-rich germ, leaving behind and disrupts the starch structure, rendering it almost pure endosperm fragments. These pre-gelatinised and eliminating this step in the fragments can be further milled and classified brewhouse. Such heating has the added according to each brewers specific benefit of denaturing major portions of the requirements. Some grit products can be protein in the kernel, to the extent that only processed through the brewhouse without 10% of the wort soluble protein remains. additional processing, but this is dependent

upon the cereal gelatinisation temperature. Glucose syrups are mainly produced from Grits tend to have high β-glucan levels that maize and wheat. The process is outlined in increase wort viscosity and can hinder wort Figures 2 and 3. The degree of starch separation. conversion in the final syrup is expressed as Dextrose Equivalent (DE). This is a measure of the reducing power of the solution. Flours/Starch Starch and flours used in brewing For example: predominantly consist of wheat and maize, • Starch has a DE = 0 although others are used. Starch and flours • Pure dextrose has a DE = 100 are produced via the wet milling process. Flours are mainly produced through sequential milling, although hammer mills are Sucrose Syrups often used to produce the final fine flour. Sucrose syrups comprise two varieties; Refined starches are prepared as in Figure 2, sucrose syrups and invert syrups. Both are with the additional step of drying the final derived from sugar cane or sugar beet (see starch slurry to yield a “flour”. Flours can also Figures 1 below). The benefit of invert sugars be pelletised. Refined starches are the purest is the additional fermentable material extract source available to the brewer. achieved on inversion, termed the “inversion gain”. Although starches and flours can be added directly into the mash, additional storage and handling problems are incurred. Storage containers must be earthed due to the risk of dust explosions and pneumatic conveyors are needed to transport the starch. Starch flour We can see above that by transforming a collapses or “bridges” easily on leaving disaccharide such as sucrose into two storage bins, blocking vessel outlets. Storage monosaccharides (glucose and fructose) vessels with special fluidising bottoms are through hydrolysis, there is a molecular required. weight gain equivalent to a 5.26% increase.

This gain in weight is effectively transferred Additionally, grist compositions containing a into a gain in product volume. high proportion of fine flours can lead to “set” mashes, where the bed is too thick to allow efficient enzyme mixing and saccharification. KEYPOINT: The process of inversion, in relation Particle size is important, too large and to food, is the hydrolysis of sucrose by acid and/ extract losses ensue, whilst too small and or high temperatures to give invert sugar. haze and wort separation problems follow. Invert sugar is a mixture of equal parts of d- fructose and d-glucose. Most fruits contain invert sugar and Liquid Adjuncts honey contains over 70%; it is also obtained from starch. Glucose Syrups The use of syrup adjuncts has drawbacks. The term glucose in this context can be Problems include: misleading. Glucose is the most common • Storage and handling of syrups is unique. name for dextrose. In brewing, glucose It is essential to store syrups warm; if this syrups are in fact solutions of a large range of is not done the syrup will crystallise, and sugars and contain dextrose, maltose, the viscosity of the syrup will hinder, if not maltotriose, maltotetrose, and larger dextrins. halt, transfer between vessels. The spectrum of sugars in the syrup depends

upon the manufacturing process used.

o glucose syrups should be stored Malt Extracts at approximately 45°C Malt extracts are essentially concentrated syrups of wort. Malt is milled, and mashed as o sucrose/invert syrups should be usual and the wort then concentrated to a stored at approximately 25°C syrup by evaporation. They can be prepared from any range of grist components to supply • Microbial infection must be prevented; as the required specifications. Malt extracts can a result glucose syrups should contain be prepared to include or exclude diastatic 80% solids and sucrose syrups 67% solids, enzymes, as required. The diastatic malt whilst condensation must be avoided at extracts are prepared using slightly lower all costs. Maintaining the syrups at such mashing temperatures, to preserve enzyme solids loadings or concentrations levels, by avoiding thermal denaturation. Malt produces osmotic pressures within the extracts can be used to increase production syrup capacity and alter product characteristics, but due to the extra processing involved they are • that few microbial contaminants can considerably more expensive than other survive. The use of sterile air filters will adjuncts. also help.

• Worts produced with excessive Caramel proportions of sugar syrups, in particular

glucose, can lead to both increased Caramels are used to add colour to beer and diacetyl production and cause “stuck” are produced by heating invert sugars or acid fermentations. hydrolysed starches. The colour is produced

via the Maillard reaction and as such the KEYPOINT: Critical levels of adjunct syrups can sweetness of the caramel is substituted for be encountered. Excessive concentrations of extra colour. The Maillard reaction is the non- individual sugars can force the yeast to enzymatic browning caused by the reaction of suppress uptake of other sugars causing a the aldehydes or ketones present in the premature cessation to fermentation. Known reducing sugars with protein and amino acids. as a “stuck or hung” fermentation.

Figure 1 Sucrose syrup production. The syrup can be used as is or processed further to produce invert syrup.

Figure 2 The production of refined starch from Maize via the wet-milling process

Figure 3 Adjunct syrup production from starch

Use of Adjuncts in the Brewery Technically both wheat and barley can considerably improve the head retention of a Introduction product.

The Bavarian Purity Law (the Reinheitsgebot) The most commonly used adjunct materials defines an adjunct as: worldwide are maize (46% of total adjunct use), rice (31%), barley (1%), and sugars and syrups (22%). Other materials are also used, for instance potato and soya beans. “Anything that is not malt, yeast, hops or

water”.

Adjunct Type Source Today, the definition is much broader, for Basic raw cereal Barley, wheat instance in the UK the Foods Standards Committee interprets adjuncts to be: Raw grits Maize, rice, sorghum

Flakes Maize, rice, barley, oats “Any carbohydrate source other than Torrified / Micronised Maize, barley, wheat malted barley which contributes sugars to the wort,” Flour / Starch Maize, wheat, rice, potato, soya, sorghum Syrup Maize, wheat, barley, potato, An enormous and varied range of adjuncts is sucrose available to the brewer, each has benefits and Malted cereals other Wheat, oats, rye, sorghum drawbacks. Classically they can be than barley characterised by their form and application.

• Solid, unmalted cereals processed in the brewhouse. Adjunct Properties The processing properties of adjuncts are • Solid, malted cereals other than barley, related to their structure and chemistry. processed in the brewhouse.

• Liquid adjuncts, usually added to the Adjunct β-glucan Pentosans Proteins Lipids copper (kettle), or added post fermentation as primings. Barley 3.5 10 11 3.5 Wheat 0.5 8.5 12 3

Typically, adjuncts contribute no enzyme Maize grits 0.1 1.5 9 0.4 activity to the mash, which can pose Rice grits 0.1 0.5 7 0.5 problems. The major benefits of adjunct use Wheat flour 0.1 1 0.9 1 are that they contribute little soluble nitrogen, whilst purchase cost is usually Wheat starch 0.1 0.6 0.5 0.4 reduced compared to malted barley. Sorghum 0.3 2.5 11 5.0

Huge efforts are expended in improving adjunct performance and examining their contribution to final beer characteristics. In general, maize will give beer a fuller flavour than wheat, which imparts a dryness, whilst barley supplies a stronger harsher flavour.

There are 6 major adjunct attributes that stabilise beer foam (or head) by interacting affect their use during brewing: with other polymers derived from hops. By using large quantities of wheat adjunct in the 1. Decreased protein levels increase grist, the need to use synthetic head beer stability (by lowering haze stabilisers such as Propylene Glycol Alginate potential) whilst reducing the capacity (PGA) is avoided. for microbial infection, therefore improving shelf life. Generally, the protein contributed to the wort from adjunct addition is insignificant, resulting 2. Diminished levels of lipid materials in a linear dilution of wort free amino abate staling reactions and guard nitrogen (FAN). This dilution is accentuated against loss of head retention. further as malt proteases will not degrade unmalted cereals. Dilution of wort amino 3. Less cell wall material reduces β- acids can be detrimental to yeast, critically glucan and pentosan content and forcing the yeast to anabolically synthesise improving wort viscosity. the deficit. This can give rise to the production of unwanted flavours, such as 4. Different proteins and their diacetyl, a by-product of anabolic amino acid proportions present, improve head synthesis. This occurrence is most common retention. with the use of large quantities of high glucose sugar and syrup adjuncts. 5. Differing starch gelatinisation temperatures can impose additional processing steps. Adjunct β-Glucan and Pentosan Excessive concentrations of pentosans and β- 6. Altered fermentable sugar spectrums glucans can produce a highly viscous wort, affect product flavour profiles. slowing mash filtration. Barley contains the highest levels of β-glucans, pentosans, lipids and starch used in brewing. Sorghum has the Adjunct Protein lowest β-glucan content, but can release very Brewers mostly, only require protein derived low levels of extremely soluble fractions, from the grist for yeast nutrition. Diminished generating wort separation difficulties. cereal protein levels in the wort reduce haze Malting sorghum makes filtration worse by potential and susceptibility to microbial accentuating the solubility of the β-glucans, infection. Unfortunately, very rarely do but at 20% grist composition, it is much adjuncts only supply sufficient protein for cheaper than maize. yeast fermentation. Barley has the highest levels of pentosans, Wheat starch has the lowest protein levels, of however, they are insoluble in comparison to the cereal adjuncts, and would meet the those of wheat, rye, and to some extent brewers’ requirements. However, the wheat sorghum. As such, the use of the latter cereals protein gluten is far more soluble than the will create filtration problems to a significantly barley protein hordein, and consequently, can higher degree than barley. cause brewhouse problems when used at lower concentrations. For these reasons, wheat is not primarily used as a source of Adjunct Lipid starch. The lipid content of the cereal is important and should be limited to prevent the In addition to gluten, wheat also contains high occurrence of staling reactions, whilst levels of glycoproteins. These high molecular defending against loss of head retention. The weight, hydrophobic polypeptides act to lipid materials are oxidised during brewhouse

procedures, generating “off-flavours”. The Adjunct Starch and Gelatinisation lipids interact with the hydrophobic Temperature polypeptides within the head breaking their conformational structure, causing foam The chemistry and structure of starch collapse. A reduction of lipid material can be influences the way in which the adjuncts are achieved using grits (pure endosperm processed. particles) and by removing the germ from the grain. The granular starch of cereals comprises two glucose polymers:

Adjunct Sugars • Amylopectin (70-80%) Substituting grist components with differing • Amylose (20-30%) adjuncts in the mash, provides varying proportions of fermentable sugars and dextrins for the yeast to metabolise. The most important property of a starch Carbohydrate spectrums are further altered granule is the gelatinisation temperature. with differing mash temperature regimes. By This is the temperature at which the starch adjusting the extract provided for yeast dextrins are broken down to their individual growth, the end metabolic by-products, and glucose polymers. Only after thermal therefore the character of the beer will gelatinisation will the starch liquefying (α- change. For example, controlling starch amylase) and saccharifiying (β-amylase) degradation to supply an optimal sugar- enzymes operate efficiently. dextrin balance is thought to enhance mouthfeel.

As an example of the varying use of adjuncts, wheat flour can be used up to 10-15% of grist composition, but use of wheat starch is acceptable up to 40-50%. Wheat starch can be used in greater proportions because, after additional processing, it contains reduced levels of β-glucans and pentosans than wheat flour. The wheat flour will create an exceptionally viscous wort at 40-50% grist composition, demonstrating how the Figure 4 Properties of starch from various cereals. structure of the grain affects processing properties.

Starch Structure Priming Sugar (Primings) Granules have partly amorphous and partly Some ale brewers provide additional crystalline (structured) sections. These fermentable materials for “Live” beers in cask structures produce a layered composition, using priming sugar. Cask or real ales contain which generates the characteristic “Maltese residual yeast in order to condition the beer, cross” appearance when viewed under the but primarily to carbonate the beer. microscope in polarised light. When Primings can be specifically designed to gelatinisation is complete and the crystalline provide a desired carbohydrate spectrum or structure disrupted, the black “Maltese cross” simple syrup adjuncts can be used. can no longer be observed. This is because

the light is no longer polarised.

and starches may demand installation of specialised pneumatic conveyors. Consequently, extra costs are incurred in the form of further labour, CIP, maintenance expenditure etc.

Commercial Enzymes in Brewing

Commercial enzymes in brewing refer to those not derived from any of the grist components. It is advisable that in most instances, adjuncts should comprise no more than 30% of the total extract source, otherwise malt enzymes and nitrogen levels are critically diluted. When pre- cooking an adjunct in a cereal cooker, 5% of the total grist malt fraction is often added Figure 5 Polarised light assessment of starch degradation. providing hydrolysing enzymes to assist starch degradation. If enzyme deficits are still Why should the gelatinisation temperature apparent, a wide range of commercially cause a problem? Typically, mashing systems prepared enzymes can be used. are not operated at temperatures above 65°C, as the starch degrading enzymes will be The use of commercial enzymes is not entirely denatured and cease to function. This is restricted to compensating enzyme further complicated by the fact that the more deficiencies, however, and they can also be abundant, small B-Type granules possess employed for: higher gelatinisation temperatures than the large A-Type granules. • Adjusting wort and beer sugar spectrums. • Sugar and syrup adjunct manufacture. As such, adjuncts with gelatinisation • Clarification purposes. temperatures greater than 65°C cannot simply be added to the mash as part of the normal grist bill, otherwise the starch will not Today, commercial enzymes are manufactured degrade. This gives rise to extract loss and from deep, stirred microbial cultures, usually potential for carbohydrate haze formation. fungal or bacterial e.g. Aspergillus spp., Bacillus subtilis, and Penicillin spp. They can be Additionally, unconverted starch will increase supplied in solid or liquid forms and are often wort viscosity and hinder separation and run- mixed with carrier substances depending on off in the lauter tun. The starch will continue the brewers requirements. to pass through the brewhouse and generate uncontrollable carbohydrate hazes, affecting The various types of enzymes available to the beer stability and shelf life. brewer are as follows:

In order to overcome the problem of critical • Heat stable α and β-amylases mashing temperatures, supplementary plant • Amyloglucosidase hard ware is necessary. This takes the form of • β-glucanases cereal cookers. Cereal cookers pre- • Papain cook/gelatinise starch from adjunct cereals such as maize, rice and sorghum. Further milling equipment, and storage requirements may also be needed, whilst the use of flours

α- And β-Amylases Other Enzyme Preparations Heat stable α-amylase can be added to the Mixtures of enzymes are also commercially cereal cooker to liquefy the adjunct starch. produced. For instance, preparations Malt derived α-amylase is heat labile and consisting of α and β-amylases and β- would denature under pre-cooking glucanase can be used where under-modified conditions, resulting in extract loss. The malts are causing bewhouse losses. addition of β-amylase to the mash, in addition to malt enzymes already present, can speed Glucose oxidase can be added to the mash. up the saccharification process whilst increase This scavenges oxygen and helps guard the fermentability of the wort by degrading against staling reactions. more starch derived dextrins. Heat stable enzymes can be deleterious as they can Preparations of diacetyl reductase can be survive boiling, and actively continue to added to beer during maturation, this assists impart additional sweetness by degrading in the conversion of the vicinal diketones to dextrins to glucose. the inactive diols, with an improvement in flavour.

Amyloglucosidase Amyloglucosidase (AMG) acts in a similar Enzyme Production Considerations manner to β-amylase, by completely Commercial enzymes are undoubtedly an degrading liquified starch to glucose. important tool for the brewer but However, AMG is of little benefit in the mash mismanagement and impure products can be tun as its hydrolysing action is too slow, but it more harmful than beneficial. Enzyme is invaluable in the production of preparations should have the following glucose/fructose syrups. AMG has also been characteristics: used to obtain highly attenuated beers and as a replacement for priming sugars. • Preparations must be stable and consistent.

β-Glucanases • Pure and free from residual production β-glucanses prepared from bacterial sources, contaminants e.g. bacterial proteases. are more heat stable and therefore, more useful than the heat labile fungal • Cannot contain any microbial hazards preparations. β-glucanase is used to degrade (mycotoxins etc.) or contain viable cell wall material, reducing wort viscosity and organisms or spores. avoiding wort separation difficulties. Such enzymes are often applied when barley is • No side activities. Commercial enzymes used as an adjunct, as it contains large can contain other enzymes as impurities. amounts of β-glucan. e.g. a bacterial α-amylase may also have a high β-glucanase activity.

Papain Adjunct Considerations Papain is a proteolytic enzyme prepared from the latex of the papaya plant. It is used as a The Darcy equation explains the general corrective measure to degrade the protein- principles behind wort separation, called polyphenol haze complexes that form as chill lautering. The equation is not totally haze. However, the addition of papain is by appropriate for the lautering procedure as the no means ideal, it is a non-specific enzyme equation expresses relationships based on and may degrade foam positive proteins incompressible beds, such as sand filters. causing diminished head retention. Lauter beds, unlike sand filter beds are

compressible. Therefore, during lautering, bed height decreases due to the drag force exerted by the wort flow, reducing the porosity of the bed and hindering run-off. To compensate, for this bed loadings above 240 kg/m2 are to be avoided, whilst grist composition should not contain excessive levels of fine particles which will “blind”, or block the filter bed.

Darcy Equation

Q = Total volume of liquid percolating in unit time.

A = Constant cross sectional area L = Filter bed depth K = Filter bed permeability (h1-h2) = Pressure drop across bed μ = Liquid viscosity

The level of adjuncts used affects the above equation and lauter performance in several ways:

• High Sugar/ High gravity worts increase viscosity and slow run-off. • Adjuncts providing high levels of cell wall material, protein and unconverted starch deposits (hemicellulose gums), blind the filter bed and can slow, or even halt, run- off. • High β-glucan levels in wort increase viscosity impeding run-off.

The overall brewing value of an adjunct can be assessed with the equation:

Brewing Value = (Extract + Contribution to beer quality) – (Brewing Costs)

Speciality Malts White Malts The palest of the malts produced is the white Introduction malt (attaining a colour of 2 EBC units). Thanks to the skilful manipulation of the Lightly kilned, with an air on temperature not malting and kilning regimes, the maltster is exceeding 70°C, white malts retain a large able to produce a diverse and vast array of proportion of their enzyme activity. The lack malt types. The brewer can utilise this of real heat treatment restrains the extensive malt family to craft beers with a development of flavour compounds producing multitude of qualities to satisfy the ever malt with a neutral, slightly sweet taste. challenging consumer. The assorted malts Often the grassy, aldehydic aromas will range from lightly coloured white malts remain along with sulphidic and DMS tastes through to charred black and chocolate malts, due to the lack of heat to drive them off each imparting their own unique colourful during kilning. and aromatic qualities to beer. In addition, not only barley can be malted; the range of malts available can be extended by use of Wheat Malts malted wheat, oats, rye and sorghum. Wheat malts differ from their sibling barley malts due to physical composition. Wheat has The primary factor influencing the colour and no husk, and as such hydrates quicker during flavour of the malt produced are the steeping than barley to generate higher temperature and extent of kilning to which extract values. The contrasting chemical the green malt is subjected. However, we can composition of wheat also gives the malt an not forget the biological nature of the grain altered characteristic. Wheat contains more and the purpose for which it is intended (to protein than barley, which gives the resulting provide extract and the diastatic power beer a fuller mouth-feel and enhanced head required to yield this extract). The highest stability. Wheat malt is notoriously difficult to coloured malts contain little, if any residual produce, is often undermodified with reduced enzyme activity after kilning, and it is essential friability and can generate viscous worts. to bear this in mind when setting your grist Compared to barley malt, wheat malts recipes. produce turbid, physically unstable beers. Wheat malts tend to have a colour of KEYPOINT: The colour of malt is measured in approximately 2 EBC units EBC units. Wort is produced from a laboratory extract of malt and the colour determined by a spectrophotometric method. Lager/Pils Malt The very pale Pilsner malts tend to be made from plump, two-rowed barley with Total Nitrogen (TN) contents of 1.52-1.84%. The barley is steeped to achieve moisture content of 43%, which after a long, cool germination period (below 17°C) produces fully modified malt. This green malt is dried quickly at cool temperatures (around 50°C), with rapid airflow to around 8% moisture before final curing at 70-85°C. These malts are characteristically very pale with no trace of caramel or melanoidin colour formation, and have weak Figure 6 Comparative ranges in the composition of barley and malt. aromas.

The UK lager malt has evolved into a very

pale, well-modified malt produced from two- Finished pale ale malts have high extract rowed barley with moderate TN contents of values and moderate TSN values, commonly 1.65-1.8%. These malts are lightly kilned to 0.5-0.7%, with TSN: TN ratios around 40%. produce characteristics that closely match the Colours range from 4-6.5 EBC units. Kilning European Pilsners. Historically lager malts regimes are sufficient to drive off any grassy were undermodified, but this is no longer true notes and remove the DMS precursors to and the light curing to which they are subject produce a characteristically malty, biscuit permits considerable enzyme survival, flavour with toffee and caramel notes generating high extract yields - often more provided from the increased Maillard reaction than the pale ale malts. products.

Kilning “air-on” temperatures are in the range The mild malts are prepared in a very similar 50-70°C and curing around 85°C, which is manner to the pale ale malts. They are adequate to effect removal of most of the subjected to higher curing temperatures of green, grassy aromas produced from oxidised between 110-140°C. This provides these mild lipids, but insufficient to break down the DMS malts with rich nutty, toffee and caramel precursor (SMM). This is acceptable in lager flavour characteristics. malts and is often specified. However, a stand of at least 30 minutes is required during wort boiling to ensure DMS control. Malt moisture levels are typically 4-6%, colours ≤ 3 EBC units, and TSN values between 0.5-0.7% giving a lightly coloured malt with a malty, biscuit- like flavour.

Pale Ale and Mild Malts The pale and mild ale malts are typically used when producing traditional British top Figure 7 Representative IOB standard analysis values for a sample of typical fermented beers and cask conditioned ales. UK floor-malts. The pale ale malts are produced using the best two-rowed barley, with low nitrogen contents ideally 1.5% TN. This lower protein Vienna Malts content helps achieve the required good clarification and physical stability of these Vienna type lager malts or Wiener malz are beers. much darker than their UK counterpart lager malts, attaining colours of between 5-10 EBC units. These tend to be mid-range values of • If slightly less well modified malts are the Pilsner and Münchener (Munich) type used head retention is favoured. malts. Vienna malts are used as part of the

grist in the production of dark, European • Under-modified malts generate poor golden lagers. Two rowed barley, that have extract recoveries, hinder wort filtration higher than average protein contents, are and instability. commonly used to achieve increased colour.

The malts tend to be well, but not over- • Over-modified malts give wort separation modified, and production often encapsulates problems, lend a thin character to the raised germination temperatures on the final beer, and produce weak head retention. day.

• Losses can also be incurred as over- Kilning initiates with a slow re-circulation of modified malts break up easily when air to promote the development of the handled. soluble sugars and amino acids that take part

in the Maillard reaction generating the typically noted as “sweet biscuit” and full, but flavoured melanoidin pigments. little caramelised flavour. A process that Paradoxically, compared to the Carapils® effectively liquefies, mashes and re- malts, endosperm liquefaction must not occur crystallises the starch produces Crystal malts. during kilning. Once hand-dry, the kilning regime is ramped up and curing set at around Crystal malt (hence the name) are the only 90°C to impart the dark colour and strong malts that truly undergo complete nutty, toffee flavour, whilst limiting the biochemical transformation of the starch to enzyme content of the malt. sugar. The green malt is deliberately held wet

Crystal malts are currently prepared using Munich Malt fully modified (not over-modified) green malt Munich malts (Münchener Malz) have that is steeped to effect re-wetting, up to 50% characteristically high melanoidin contents moisture, and loaded into a roasting drum. producing dark, aroma-rich malts (strong Initially the drum is fired directly at about nutty flavours) and are typically used for 50°C to remove any surface moisture from the brewing strong, full-bodied dark lagers. The grain. After this the drum is closed to prevent barley used has high nitrogen values, excess evaporation before the temperature is moisture contents greater than 45% and are steadily raised to 65-70°C via external heating ® permitted a long, warm germination period. (Carapils malts are dried at lower Today single deck kilns are used to kiln the temperatures, in the range of 55-60°C). This green malt, where it is held in warm re- generates the maximum yield of reducing circulating air for an extended duration, which sugars, completely replacing the endosperm slows evaporation and further effect with a clear sweet liquid. When this grain is endosperm modification. This allows the squeezed sugary liquid comes out. At this accumulation of reducing sugars and amino point the temperature is increased (suddenly acids for colour and flavour formation. or incrementally) to 100°C in order to dry the grain and re-crystallise the sugars. The final These highly coloured (15-30 EBC units) and curing temperature can be as high as 120- flavoured malts (mainly imparted by 160°C for more highly coloured products. pyrazines) have slow conversion times and reduced extract yields, combined with On slicing the crystal malt grains open at least reduced fermentability due to their poor 90% should appear hard and glassy, as ® enzymatic content. However, due the high opposed to the Carapils malt which remains buffering capacity and reducing power of the floury and mealy. With both malt types, resulting wort, derived from the high changing the initial moisture content of the melanoidin content, beers with good stability grain and kilning regimes will alter the are produced. characteristics of the product.

Crystal malt grains are smooth, round and Crystal and Carapils® (Caramel) Malts swollen whilst evenly coloured and bright. Final colour values attained are around 15-35 Carapils® and crystal malts are distinctly EBC units (Carapils®) and 10-40 EBC units different from the rest of the malt family due (Crystal). However, some British caramel to the physical and structural change that the malts achieve colours in excess of 300 EBC endosperm starch undergoes. With Carapils® units with values around 140 EBC units the malt, warm air is circulated around the wetted most popular. grain encouraging the degradation of the

starch and proteins into sugars and amino • Crystal malts when added to the grist bill acids. Once the majority of the conversion is give beer a characteristic flavour with complete, the grain is heated to generate colour and a glazed appearance, with flavours

greater body and enhanced haze and produce special ales with golden, ruby red flavour stability. hues and dry palates. Extract values are typically 270-285 l°/kg, colour 35-85 EBC units • The crystal malts provide ruby red colours and low moistures around 3.5%. and rich, sweet, full caramel flavours.

• Caution must be taken when using grists Chocolate and Black Roasted Malts comprised of more than 8-12% crystal malt. At this ratio astringent notes can be Chocolate and black roasted malts are very produced. dark coloured products that have no enzyme capacity. They have quite distinct characters, • Caramel malts impart more palate which are different to any of the coloured fullness, and head formation/retention to malts already discussed. Plump barley with a the beer. modest nitrogen content (1.5-1.7%) is used and is less modified than typical lager malt. • A slight red hue is imparted to beer when using caramel malts, in association with The kilning temperature is gradually increased light flavours whilst also contributing to final curing temperatures of 215-225oC. body. The colour of the grain is frequently checked throughout production and when the • As progressively darker malts are required degree is obtained heating is produced the flavours they impart stopped and the roasting process halted by develop and become increasingly toffee- quenching the grains with water. This causes like and malty, providing aromatic, the grain to swell. In total around 15% of luscious honey-like notes. grain dry weight is lost during the process as dust and fumes. • Extracts for both malt types are in the range 260-285 l°/kg with moistures Depending upon the quality of product the between 3-7.5%. malt will be chocolate brown to black, the husk should appear shiny and polished, and KEYPOINT: Roasted malts start their life in the when the endosperm is cut open it should be same manner as any other malt. Initial drying floury, mealy and friable not steely or charred. is at relatively low temperatures, but the later conventional drying is superseded with • Pale chocolate malts attain colours of extremely high air temperatures effected about 500-600 EBC units. through the roasting drum, at the expense of total enzyme destruction. • Standard chocolate malts have between 900-1100 EBC units colour units.

Amber Malt • Black malts achieve colours in the range 1,150-1,300 EBC units. Open coke-fired kilning was used at one time to produce amber malts. This no longer • HWE for both are in the range 255-275 occurs and roasting drums are now utilised, l°/kg and moistures approximately ≤ 2%. hence the finished malt no longer has a smoky flavour. It is normal for finished malt (pale ale Chocolate malts impart a coffee caramel, or more commonly mild ale) to be directly burnt flavour mainly provided by pyrroles and heated within the roasting drum with pyrazines from the Maillard reaction and temperatures reaching between 49°C and black malts impart an acrid sharp taste. 170°C. These malts are amber coloured, Chocolate and black malts are used in sweet impart a pleasant, dry, biscuit-like flavour with stouts and dark beers, whilst in small toffee undertones. Amber malts are used to

quantities they can be Figure 8 A schematic representation of malt production. added to cask conditioned beers to provide a deeper colour in combination with a fuller flavour with a final hang or bite. Typically addition rates are 1.5-3% of the total grist.

The grains typically appear reddish, shiny and Roasted Barley black whilst swollen to almost double the size, To produce roasted barley, grain at consequently approximately 50% will be split. approximately 2-16% moisture is directly fired Roast barley has a very different flavour than in a roasting drum for around 2.5 hours. The the roasted malts and is described as sharp, malting quality of the grain is irrelevant. Over dry, acidic, astringent and burnt whilst the first 2 hours the temperature within the providing no sweetness. Roast barley drum is raised from 80°C to 230°C. This achieves colours in the range 1200-1400 EBC effects very rapid colour formation that needs units with extracts around 260-275 l°/kg and to be frequently monitored by inspecting the moistures of ≤ 2%. Roasted barley is mainly grain every 2-3 minutes. The heat applied to used to produce stouts. the grain in the final stages is reduced to 215°C. At this temperature roasting is halted and water is used to cool the grain and prevent combustion (a massive risk in roast houses).

Self-Assessment Questions

When answering any of the Self-Assessment Questions try and link the process with the scientific theory. They can never be separated in practice. Good luck with these, give them your best shot and don’t get disheartened if you aren’t quite right, it will come eventually.

1. What is an adjunct?

2. How are adjuncts classified? Give examples.

3. What brewhouse processing procedures would you use for the following adjuncts?

 Maize grits + rice  Flaked barley + Torrified wheat  Wheat starch  Roasted barley  Invert sugar

4. Currently the wort you are producing in the brewhouse is drastically out of specification. Wort gravity is too low, mash separation is hideously slow, the subsequent fermentations are not fully attenuating and the beer produced is throwing a haze. What would you do to correct this and explain your reasoning?

The grist recipe for this particular brew contains:

 35% Malt  50% Glucose syrup  15% Barley

5. Your Sales and Marketing colleagues are not happy with one of your beers. They want a much redder hue instead of the present murky brown. What changes are you going to make to the malt grist?

Self Assessment Answers

1. An adjunct can be defined as “Any carbohydrate source other than malted barley that contributes sugars to the wort”.

2. Adjuncts are typically classified according to their form and application, for example, solid and liquid adjuncts. Solid adjuncts can then be further subdivided into malted (e.g. wheat malt) or unmalted cereals (e.g. maize grits). Liquid adjuncts can also be subdivided according to type. Adjunct syrups can be used either in the brewhouse (e.g. invert syrup) or post-fermentation (e.g. primings). Malt extracts, can either be added pre- or post-fermentation.

3.  Rice is usually supplied as grits, but otherwise may require milling. Both maize grits and rice require pre-cooking in a cereal cooker, prior to addition to the mash. They both require pre-cooking due to their higher gelatinisation temperatures; too high for typical mashing regimes. With any pre-cooking in the brewhouse, it is standard procedure to include between 5-10% of the malt grist to allow enzymatic degradation pre- or post- gelatinisation. This is an important additional step that acts to reduce the viscosity of the mash facilitating rapid and easy transfer to the mash tun.

 The flaked barley and torrified wheat can be added directly to the mash tun along with the remaining grist. The flaking and torrifiying procedures pre-gelatinise the starch and therefore, these adjuncts require no pre-cooking.

 The wheat starch can be added directly to the mash, it requires no milling and with a starch gelatinisation temperature below that reached during normal mashing regimes, requires no pre-cooking.

 Roasted barley needs no pre-cooking step due to the partial starch pre-gelatinisation effected by the roasting process. However, as with unmalted barley, separate milling from the grist may be required due to the structural integrity of the grain.

 Invert sugar can be added directly to the copper (kettle) as it requires no pre- gelatinisation, it is simply a sugar solution. However, it is good practice to stagger the addition of the syrup proportionately between the coppers in use. For example, 15-20% of the total syrup volume used should be added to the first (strong) worts collected. Then as the weaker worts and final runnings are collected into the second and third coppers respectively, the amount of syrup added to each can be increased. Approximately 20-30% into the second copper and 50-65% into the third copper, according to the original gravity of the wort. This distribution will help prevent excessive evaporation and colour formation in the copper that could result from extremely strong first worts and weak final runnings.

Another important concern when pre-cooking is the addition of the “cook” to the mash. The whole practice of pre-cooking the cereals is because they require processing at much higher temperatures than

the mash will permit. If the cooked cereals are then added directly to the mash, the temperature increase will be sufficient to destroy the enzymatic integrity of the mash and render the process futile. Therefore, when utilising pre-cooking procedures, a much lower primary mash temperature must be used (48-50°C) so that on addition of the hotter “cook” the temperature of the mash will not be raised above critical temperatures where enzyme degradation will occur (>68°).

Often the same points will arise time after time after time, e.g. wort viscosity, haze potential, beer stability. This is due to the inherent overlap between the process components and their actions. Try and think of the process as whole and not as separate component systems.

4. Check lab analyses of all the raw materials. Is the malt sufficiently modified? If not, incomplete breakdown of cell wall materials will restrict starch extraction (reducing the potential gravity achievable) and produce viscous worts. Is the diastatic power of the malt sufficient to achieve starch degradation and release the full extract potential? Incomplete gelatinisation may also be contributing to the haze problem, (carbohydrate haze). Under-modified malt could also provide the proteinaceous haze pre-cursors, whilst there could be insufficient FAN for an active fermentation.

The grist cereals could be checked against specification. It is possible that high β-glucan and pentosan levels contributed by the cell walls influencing the viscosity of the wort, whilst the elevated protein levels are amplifying the haze problem.

Incomplete attenuation can more than likely be attributed to the glucose syrup. At 50% grist composition the high level of glucose may be causing stuck fermentations through catabolite repression. High glucose concentrations suppress the uptake of other sugars by the yeast. Critical dilution of the wort protein content can also cause stuck fermentations through a change in pH. If the protein content of the wort is too low there will be no pH buffering action. Therefore, as the fermentation proceeds the pH can drop and inhibit cell growth and halt the progression of attenuation. In practice total adjunct use will rarely exceed 40%. Many brewers consider this high.

Is the process itself at fault? Is the mash regime OK? Is the temperature too high, denaturing the enzymes leading to incomplete starch breakdown? Is the grist: liquor ratio acceptable, or is the mash too thick (a set mash)? This could explain reduced extract and gravity potential, and carbohydrate haze formation.

Milling could be the cause of the problem:

 If the grist is ground to fine flour then this could lead to viscosity problems with the wort.

 Or if particles are too large this can lead to extract loss.

5. The murky brown hue in the beer at present is probably due to the use of chocolate or black malt as the main colouring agent. If we were to replace this with crystal malt, the beer hue would appear redder.

from two sources: 1.1.3 WATER • Surface waters (e.g. local borehole Introduction supplies, wells, and rivers). • Municipal water supplies. Quantitatively water is the predominant

brewing raw material with most beers The surrounding topography and geology of composed of 90-95% water. Therefore, the the extraction point, whether borehole or condition of this water is of paramount municipal supplies influence the importance to the brewer, as this will have characteristics of the water. Certain water consequences for the quality of the beer. The types (in terms of their mineral composition importance of water used in the brewing and hardness) are particularly suited to industry is traditionally so significant (in terms brewing. Towns and cities with high quality of availability and suitability) that the location water supplies have traditionally become and survival of a brewery has been established brewing centres, often renowned determined by its water supply. for producing their own typical beers. For

example, Burton-On-Trent (England) for its It is easy to ignore the fact that water has its pale ales, Dublin (Ireland) for its stouts, own unique taste and that this taste differs Munich (Germany) for its dark lagers and from city to city, and country to country. Let Pilsen (Czech Republic) for its pale lagers. us consider the production of the same beer in different worldwide locations. If the The dependency of the brewing process upon production conditions are the same, in each its water supply is apparent when we consider brewery, then any differences in taste may be that on average 6 hl of water are needed to attributed to the different water source – produce 1 hl of beer. Of course not all of this even if the beers are intended to be the same. water ends up as beer.

Water Source and Application

Water is increasingly a scarce resource and brewing is a water intensive process. Today the brewer may have the option to draw water

Figure 9 Representation of brewery borehole.

Water is also used for:

• Brewing and processing • Dilution of high gravity beer • Cleaning plant equipment • Bottle washing • Pasteurisation • Boiler feed water • General amenities

Figure 10 Analyses of typical water qualities used around the world for brewing (ppm or mg/l).

Figure 11 Typical distribution of optimal water usage within a brewery.

The luckiest brewer in the world is the one imparting its own characteristic traits. The whose water supply is pure, clean, untainted chemical composition of water provides and free from microbial contamination and of essential minerals, which fortify the wort. course free of charge! In reality this is never These minerals aid yeast during fermentation. the case. Before brewing the water must be analysed to ensure it is suitable for human In general terms the composition of brewing consumption. liquor can influence the production and quality of beer in three areas: What are the desirable characteristics of brewing water? In general water used for • Mineral composition and pH (see section brewing should be analysed for the following: 1.5.2). • Microbial contamination - leading to beer • Microbiological content: coliform spoilage. bacteria are indicative of water purity • Inorganic and organic compounds and with safety levels stipulated at 0 cells/ 100 flavour taints. ml water. What implications does the water • Colour and clarity: suspended solids can composition have for the brewer? cause increased colour and haze.

• Taste and odour: water treatments such Inorganic and Organic Compounds as chlorination can affect beer flavour. The worlds water resources are increasingly becoming contaminated by inorganic (nitrates • pH: water should optimally be slightly and heavy metals) and organic compounds acidic or close to neutral pH (7.0). (pesticides, fungicides, fertilizers, phenols, mineral oils and polyaromatic hydrocarbons). • Heavy metal ion concentration: all With the use of intensive agricultural practice potable water should be free from such more nitrate is leaching into the rivers and compounds on health grounds. water aquifers. These nitrates inhibit yeast growth leading to sluggish fermentations and However, ask yourself how much control we high levels of diacetyl. More worryingly these should apply to our water intake? Let’s think nitrates can also be converted into about it. The water coming in to our brewery carcinogenic non-volatile nitrosamines, has an intolerably high microbe count; yet all referred to as Apparent Total N-nitroso other parameters are suitable and within Compounds (ATNC). specification for production. Should we sterilise, at great cost, all water supplied to There are other materials produced from the the brewery? If we were to do this we would reaction of organic compounds in the water be wasting both resource and money. Boiler that detrimentally affect beer quality. For feed water, for example, is not used for beer example, trihalomethanes and chlorophenols production and is sterilised due to the nature are produced from the reaction of chlorine of the operation. Think carefully about the and organic substances. A vast number of application of your brewing liquor and its these compounds have extremely low flavour treatment requirements. thresholds (below 1 ppb) which can impart undesirable medicinal, phenolic traits to beer.

Water Is More Essential Than You Think! Microbiological Contaminants Why is water more important than we first Brewers need to guard the sterility of the beer imagine? Water is important in determining from fermentation onwards, knowing the the taste profile of our beer, simply through impact that microbial contaminants play

regarding beer stability, health and safety and two types of hardness: in addition fermentation performance efficiency. The preceding brewhouse • Temporary Hardness operations of mashing and boiling are considered sufficient to combat any posing • Permanent Hardness microbial threats. Remember though that not all brewing liquor incorporated into beer passes through the brewhouse. High gravity Temporary Hardness dilution water and CIP final rinses are two KEYPOINT: Temporary hardness of water is caused examples where microbiologically sterile by the presence of the hydrogen carbonates of water is essential. calcium and magnesium. They are removable by boiling which precipitates the carbonate. Brewers rarely have to worry about the microbial quality of water coming from Temporary water hardness is caused by the municipal supplies. Water authorities and presence of calcium and magnesium hydrogen suppliers in Europe are subject to rigorous carbonates (or bicarbonates). Permanent regulations such as the EC drinking water hardness, however, is due to the presence of directive in Europe (80/778/EEC). If a brewery mainly sulphate, chloride, and nitrate salts of uses water from a private well or borehole calcium and magnesium. The hardness of then it is necessary to treat the water before water has the ability to influence the pH of use. brewing liquor and therefore can affect the production process. The ions causing temporary hardness generally raise the pH Water Hardness whilst the ions causing permanent hardness, tend to lower the pH. KEYPOINT: Hardness is a property of water, which leads to difficulty in forming soap lather. This is due to the presence of calcium and magnesium cations in solution.

Examples of water hardness can be seen around our homes that are also common to the brewery. After considerable use of an electric kettle the heating element inside tends to “fur up” and in a similar manner, Equation 1 describes what happens when steam boilers and heating surfaces in the water with temporary hardness is boiled. brewery are subject to the same problem. Calcium carbonate is formed and precipitates Another crucial impact of water hardness is out of solution whilst the carbon dioxide is the ability of the minerals in solution to adjust released. Studying equation 2 (a detailed the pH of wort. Water hardness has the breakdown of what is happening to these potential to affect the brewing process in two compounds) we can see that these ways: compounds act as weak bases and raise the

pH of the water (or mash) because hydroxyl • Limestone scaling (which leads to reduced ions (OH-) are produced and carbon dioxide heat transfer efficiencies). (which is acidic) leaves the system. • Adjustment of wort pH (leading to altered

wort composition and fermentation Alkaline worts are detrimental as they can performance). cause:

Water hardness is almost exclusively • Poor saccharification. dependent upon the calcium and magnesium • Poor wort separation. in solution. Water can be categorised into

• Reduced extract. (NaOH) to an indicator end point using Patton • Dark worts. and Reeders Reagent Indicator. Calcium • Poor biological stability. hardness is expressed as CaCO3 – were 1 ml of • Poor protein precipitation. the EDTA solution is equivalent to 1 mg of 2+ • Astringent beer (polyphenol extraction). Ca .

Magnesium Hardness Permanent Hardness This is the difference between the total Unlike the weak alkaline bicarbonate salts of hardness and the calcium hardness, for calcium and magnesium – the acidic example: sulphates, chlorides and nitrate salts decrease the pH of the liquor and wort due to the • Total hardness = 278 mg/ litre expressed release of hydrogen ions (H+). A large number as mg of CaCO3. of substances such as phosphates, organic • Calcium hardness = 108 mg/ litre acids, phytates and proteins are extracted expressed as mg of CaCO3. from the malt and it is these that interact with • Therefore Magnesium hardness = 170 the calcium and magnesium salts to release mg/ litre expressed as mg of CaCO3 the H+ ions to reduce pH. The example below illustrates how phosphate complexes interact with calcium ions to release hydrogen ions. Total Alkalinity

This is estimated by titrating 100 ml of water with 0.1 N HCl to pH 4.4 using bromocresol green or methyl orange indicator. This titration measures the bicarbonates, It is essential therefore that the pH of the carbonates and hydroxides of alkali and water used for making beer is balanced and alkaline earth metals with hydrochloric acid. several methods can be employed to achieve. Alkalinity is expressed as mg of CaCO3 – were

1 ml of 0.1 M HCl is equivalent to 5 mg of KEYPOINT: Phytic acid, which is derived from the CaCO3. aleurone layer of malt, reacts in a similar manner to

phosphate complexes with calcium but has an increased affinity for this ion. As well as treating brewing water it is It is believed the drop in pH is also due to proteins necessary to treat boiler feed water, since reacting with the calcium. hard water leads to a build up of scale with a loss in boiler efficiency. The methods

commonly used to treat boiler feed waters Measuring Water Hardness vary with the type of boiler; usually the choice is between chemical treatment with lime and Total Hardness ion exchange.

This is calculated by titrating 100 ml of water buffered with ammonia/ammonium chloride Brewing Water Ionic Content with 0.02 M EDTA to an indicator end point using Eriochrome Black Indicator. Total Calcium (Ca2+) Hardness is expressed as mg of CaCO3 – were 1 ml of the EDTA solution is equivalent to In addition to its prominent role in water hardness calcium ions have a beneficial input 1 mg of CaCO3. to the production of beer. Calcium is

responsible for reducing pH throughout Calcium Hardness mashing, boiling, and fermentation. By reacting with buffering compounds such as This is obtained by titrating 1 ml of EDTA polypeptides, amino acids and phosphates buffered with a strong alkaline solution

calcium forms insoluble compounds that Magnesium (Mg2+) precipitate out of solution, consequentially + Magnesium salts give similar reactions to releasing hydrogen ions (H ) that force a calcium, but are more soluble in water. reduction in pH. Magnesium salts at levels above 15 ppm give a sour, slightly bitter taste to beer whilst A reduction in the mash and wort pH resulting magnesium salts in excess can unfortunately from the addition of calcium compounds cause flatulence, even laxative effects in combined with the presence of calcium ions humans. Importantly magnesium acts as an already present results in the following: enzyme co-factor in yeast.

• Increased wort fermentability. • + Improved extract recovery. Sodium (Na ) • Increased wort free amino and soluble nitrogen. Sodium imparts a sour, salty flavour to beer • Increased rate of mash tun run-off. (especially as NaCl) and this is true for • Reduced extraction of tannins and silica concentrations of approximately 150 ppm. compounds. Lower concentrations (75 – 150 ppm) of sodium can provide sweetness and palate • A reduction in wort pH does have a fullness. negative impact upon hop utilisation. α-

Acid isomerisation is most efficient at an alkaline pH although some say the + Potassium (K ) bitterness produced at lower pH is “finer”. The effects of potassium are similar to that of Calcium has other benefits not directly related sodium imparting a salty characteristic, but to pH: unlike sodium it is not usually added to water used for brewing. In excess, potassium can • Improved protein precipitation and induce laxative effects. restricted colour development during the

boil. 2+ • Improved yeast flocculation. Iron (Fe ) • Improved beer stability due to the The presence of iron in wort and beer is augmented removal of oxalic acid as detrimental and should be absent from calcium oxalate (beer stone) minimising brewing water or at least present in quantities the potential for haze formation and less than 0.2-0.5 ppm. Iron prevents the gushing. saccharification of the mash and disables the • Protection of β-amylase from thermal yeast producing insipid beers lacking body and denaturation extending its effective palate fullness. Iron acts as a catalyst in activity. packaged beer for the auto-oxidation of • Stimulates amylolytic and proteolytic polyphenols. Iron then promotes and enzyme activity, which improves accelerates the formation of permanent brewhouse extract. hazes. Iron itself imparts a strong metallic, astringent flavour tainting the beer.

Zinc (Zn2+) Zinc is an important mineral and is often found as a component of yeast food. In trace amounts (0.15-0.20 ppm) zinc is a yeast nutrient involved as an enzyme co-factor that Figure 12 The effect of Mineral Composition of mash water on wort pH. is required for normal metabolic processes and if limited can restrict fermentation. At

- high concentrations, however, zinc becomes Nitrates (NO ) toxic to yeast whilst it also inhibits amylase 3 activity and is a haze promoter. With intensive agricultural practices more nitrate is finding its way into water supplies where in conjunction with microbial Copper (Cu2+) contamination in wort and beer can form carcinogenic non-volatile ATNCs. It is Copper is not a mineral brewers really want in recommended that the total ATNC level in brewing water. Copper is toxic to yeast at beer should be less than 20 ppb. levels above 10 ppm, but even at lower

concentrations it accelerates polyphenol auto- The problem is reduced by careful attention oxidation catalysing the formation of to: undesirable hazes.

• The nitrate content in the water. - • Type and quality of the hops. Chloride (Cl ) • Standards of plant hygiene to eliminate At levels up to 300 ppm chloride ions increase nitrate reducing bacteria. palate fullness, whilst providing a mellow flavour. In addition chloride improves clarification and colloidal stability but at Microbiological Treatments concentrations higher than 500 ppm, chloride ions can restrict yeast flocculation giving Chlorine Treatment sluggish fermentations and poor beers. Chlorine water treatments incorporate the

use of chlorine gas (Cl2) and chlorine dioxide - (ClO2). Sulphate (SO4 )

Sulphate ions in water especially complexed Chlorination with magnesium impart drier more bitter Chlorine gas is slowly injected into water to flavours in beers. Sulphates are also form hypochlorous acid (HOCl). The activity precursors for SO2 and H2S that are generated of chlorine as an anti-microbial agent has not by the yeast, or contaminating bacteria, been fully determined. There are many during fermentation. theories on how chlorine exerts its anti- microbial activity; these modes of action

2+ include the destruction of key metabolic Manganese (Mn ) enzymes, interference with DNA replication, At concentrations above 0.5 ppm it may chromosomal aberration and impaired inhibit the fermentation, but it is required at microbial cell membrane function. lower levels (0.2 ppm ) when it acts as a co- factor to yeast enzymes. This is an effective sterilisation method but the risk of formation of organic halogen compounds is high which increases the risk of - taints in the beer. Nitrite (NO ) 2 The presence of nitrite indicates pollution or Advantages: contamination of the water. It is poisonous • Low initial cost. for yeast and can react with tannins to give a • Low running costs. reddish tinge to beer. Wort nitrite can • Simplicity of handling. contribute to N-nitrosocompounds in beer. • Protection against re-infection.

Disadvantages:

• Gives an off-taste that requires carbon Ozone treatment filtration. Ozone is produced by passing a flow of air or • Some organisms are resistant to chlorine. oxygen through a high voltage field in which • Formation of haloforms. the reaction 3O2→2O3 proceeds. When used in combination ozone and UV treatment Chlorine dioxide break down chlorinated hydrocarbons, by the Less is known about the anti-microbial effect following reaction: of chlorine dioxide than the other chlorine compounds and it is being used more in the food industry. The use of chlorine dioxide has advantages over the use of chlorine even at Advantages: its maximum permitted level of 0.5 ppm (in • Strong disinfecting effect. potable • Protection against re-infection.

• Removal of off-tastes and colouration. water). Chlorine dioxide is an unstable gas • Degradation of phenols to harmless acids. produced by reacting hydrochloric acid with • Degradation of pesticides. sodium hypochlorite. • Removal by precipitation or oxidation of

Advantages: iron, manganese, sulphur, hydrogen sulphide, nitrite and ammonia. • No change in taste of the water.

• Low operating costs. Disadvantages: • Safe process. • Forms haloforms unless combined with • Reliable sterilisation. UV treatment. • Effective against a broad spectrum of • High initial cost. microorganisms. • High running costs. • No formation of chloroform or other • Automatic control required. organic halogens because these

compounds are oxidised.

Sterile Filtration Disadvantages: • Chlorine dioxide must be generated in In the same manner that beer is filtered situ. through porous membranes to remove • Limited approval for use in the food microbiological contaminants the same industry. technique can be used with water. Pore diameters of the filters are usually in the range 0.2-0.45 µm. Unfortunately UV treatment throughputs can be slow and the membrane can quickly become blocked. Ultraviolet light in the range 200-280 nm works by destroying the DNA in microbial contaminants. A clean and effective process, Chemical Treatments To Remove UV irradiation is expensive but flow Hardness throughput is slow. Unlike chemical treatments, however, there is no residual There are various methods the brewer can action after application but to be effective the employ to remove or reduce the hardness of thickness of the water treatment layer must the water. The first is boiling. By boiling the be shallow, whilst highly coloured water with water for at least 30 minutes the soluble a high level of turbidity will restrict calcium bicarbonate is broken down to sterilisation. insoluble carbonate as described in section 1.5.2.1.

Using lime as a water softening process,

carried out hot or cold, reduces the hardness boiler feed and CIP to remove calcium and of the water by precipitating the dissolved magnesium ions – this water is not suitable calcium or magnesium salts as insoluble for brewing due to the high sodium chloride calcium carbonate and magnesium hydroxide, content. respectively. With this method the water must be left to stand, allowing the precipitate to settle. De-Mineralisation If hydrogen ion exchange resin is used then the calcium and magnesium (and any sodium)

Another treatment used to remove hardness ions will be replaced with hydrogen ions. The is the addition of acids. Acids such as hydrogen ions react with dissolved salts to form the corresponding acids, however, these sulphuric (H2SO4), hydrochloric (HCl) and acids need to be replaced or neutalised prior phosphoric (H3PO4) can be used to remove the carbonate and if the calcium acid is insoluble to use. part of the calcium also. However, the type of acid used can affect the ionic composition of De-Ionisation the water and the flavour of the final product. Anion exchange resin is used which exchanges sulphate, carbonates and chlorides for hydroxyl ions. Hydroxyl ions react with hydrogen ions to give pure water. The downside of de-ionisation is that silicate and Other Methods of Salt Removal organic residues are not removed by ion In addition to the chemical water treatments exchange. stated above other physical treatments are employed which not only deal with water hardness but also the composition of other Reverse Osmosis (RO) minerals. Standard osmosis involves the diffusion of a solvent through a semi-permeable membrane into a more concentrated solution; the end Distillation result is an equal concentration on both sides This process involves boiling the raw water in of the membrane. RO involves purifying a double phase change from liquid to vapour water by forcing it, under pressure, through a and back again. The dissolved materials are semi-permeable membrane that is not left behind in the boiling chamber, which will permeable to the impurities to be removed. need regular descaling for efficient operation. Beneficially the water exiting the distillation By applying pressure to water containing chamber is also sterile, but volatile impurities dissolved minerals, only the water is forced including organics can be carried over into the through the membrane (excluding particles in distillate. the range 0.00001 to 0.001 µm in diameter) for collection. The process can be considered to be forced pressure filtration than true RO. Ion Exchange Salts and contaminants are concentrated in Ion exchange is the interchange of ions of the upstream side of the membrane and can similar charge between an insoluble resin and flushed to drain. RO has the great advantage a solution brought into contact with it. Ion over ion exchange in that no chemicals are exchangers have been used for a long time in added to the water saving capital the brewing industry to remove cations from expenditure, health and safety and waste the water and reduce hardness. Sodium ion disposal. However, water destined for RO exchange is often used to soften water for must first be pre-filtered to prevent the semi- permeable membrane from blocking.

infection from the mains system and the carbon filters may require steam sterilisation at regular intervals.

Sterilisation of Dilution Water Many breweries practice high gravity brewing where the beer is brewed and fermented at an alcohol level higher than sales Figure 13 Reverse osmosis; the pressure applied to the impure alcohol level. The high gravity beer is diluted water is greater than the osmotic pressure of the solution. to the required sales alcohol level usually as part of filtration. As well as being free from microorganisms the dilution water should be Removing Organic Content very low in dissolved oxygen and this is achieved by heating the water to drive off the Carbon Filtration oxygen or sparging with an inert gas such as CO2 or N2, or a combination of the two The treatments to reduce hardness or the procedures. mineral content of the water, with the

exception of membrane separation (reverse Water suitable for blending should meet the osmosis), will not generally remove organic or following criteria: halogen contamination in the water. The • The ionic composition should be similar to presence of halogen compounds in the brewing water but lower in calcium to combination with organic material either from maintain flavour balance. the water or beer can react to produce

organic halogenated compounds such as • The bicarbonates should be reduced to trihalomethanes and chlorophenols, which avoid increase in beer pH. may give colour, taste or odour to water and

beer. • Carbon pre-filtration needs to be carried Some of these compounds can be removed by out to avoid the risk of forming clarification with the aid of flocculants such as organohalides (TCP taints) especially in aluminium sulphate or ferric salts, but a more moorland soft water areas. effective treatment is adsorption on porous • material that traps these molecules in its Sterile filtration is required (particularly pores. when deaerating with nitrogen gas) to avoid nitrosamine formation. Active carbon based on coal or coconut can be used to adsorb impurities from water either through physical adsorption into its honeycomb structure, which is a reversible process, or by chemical reaction that is irreversible. A material with high internal pore volumes favours both types of reaction.

Activated carbon has a finite capacity to adsorb chemicals, and will require replacement or regeneration depending on the level of contamination and the capacity of the filter used. The removal of chlorine from water renders it susceptible to microbial

Self-Assessment Questions

When answering any of the Self-Assessment Questions try and link the process with the scientific theory. They can never be separated in practice. Good luck with these, give them your best shot and don’t’ get disheartened if you aren’t quite right – try again.

1. Today most brewers have the option to draw their water from several sources. Can you remember what these sources are and what affects the water quality drawn from these points?

2. We know that during the production of 1 hl of beer we make use of 6 hl of liquor. The greatest percentage of this is put to use throughout brewhouse and fermentation process operations. TRUE or FALSE?

3. Discuss water hardness. What causes it, and what implications does this pose for the brewer?

Self-Assessment Answers

1. Brewers have the option to draw their liquor supplies from two sources.

A) Ground water and Surface waters (e.g. boreholes, wells and rivers) B) Municipal water supplies.

The topology and geology of the surrounding catchment area influence all water characteristics. This is augmented when water is drawn from natural sources such as boreholes. This is because municipal supplies experience compositional change during treatment e.g. removal of suspended solids or the addition of fluoride.

2. Surprisingly this is FALSE! We consume the greatest volume of water during packaging and dispatch (almost 40%). Imagine how much water a two-tier pasteuriser uses, or how much water we use washing bottles and cans. Hope this didn’t catch you out.

3. Right then. Hardness can be defined as that property of water that leads to difficulty in forming soap lather and is due of the presence of calcium and magnesium cations in solution.

Water Hardness is divided into two categories:

 Temporary Hardness

 Permanent Hardness

Temporary Hardness is caused by the presence of calcium and magnesium hydrogen carbonates, whereas permanent hardness is due to the presence of mainly chloride, sulphate and nitrate salts of magnesium and calcium. The empirical definition of permanent hardness is that which remains after prolonged boiling and is induced by magnesium and calcium chloride and or sulphates.

Temporary and permanent water hardness present differing implications for the brewer. The ions causing:

 Temporary Hardness tends to raise wort pH.

 Permanent hardness tends to lower wort pH.

1.1.4 HOPS The hop cone (the strobilus), is the productive female flower. The hop cone is made up of Introduction valueless stipular bracts and seed bearing bracteoles, both attached to the central strig. Hops have been utilised in brewing since its The lupulin glands are located at the base of early origins. Hops, other herbs and spices the bracteoles, where the seeds also develop. were probably first added to finished beer to It is the lupulin glands that provide all of the produce special flavours and cover up “off- bittering and aroma compounds utilised in flavours” imparted by microbial brewing, i.e. the bitter hop resins and contaminants. Hops are still added to beer aromatic essential oils. during production. Hop addition is historically recognised to confer bitterness and distinctive aroma or flavour to the beer, but today hops are recognised as also being able to improve beer stability (in terms of clarity), head stability, anti-microbial activity and light stability. Without hops, would beer still be beer?

Hop Biology and Structure Hops are members of the :

 Family = Cannabinaceae Figure 14 Chemical composition of whole hops.  Genus = Humulus These figures are a representative example. Remember as with any botanical, biochemical  Species = Lupulus L entity there will be varietal differences.

Hop varieties are divided into 2 distinct Although related to the cannabis plant, hops categories: (Humulus lupulus) contain none of the toxic resins associated with marijuana. The hop is a • Bittering hops perennial, climbing plant native to Asia, North • Aroma hops America, and Europe, which has also been successfully cultivated in Australia.

Figure 15 Diagram of hop cone and its constituent parts.

Bittering hops (high in α-acids) predominantly provide bitterness although they do confer aroma. Aroma hops (containing high proportions of essential oils) provide the hoppy aroma, and to varying extents bitterness. However, each will impart varying degrees of both bitterness and aroma.

Figure 16 Hop varieties and their relative uses and a-acid values.

Hop Cultivation are dried from ~80% to 10% moisture in kilns, similar to those used for malting. As a perennial crop, hops are grown from Drying prevents deterioration. rootstocks that remain in the ground all year round. They can be propagated from cuttings • The whole hops are then compressed and taken from this rootstock, from underground baled to reduce storage requirements and rhizomes or from softwood cuttings. costs. The whole hops can then be used as is, or after processing as pellets, powders, extracts.

Hop Diseases Growing hops are vulnerable to both viral and fungal attack, which if severe enough can destroy whole harvests. The main culprits are:

• Damson Hop Aphid • Powdery & Downy Mildew Figure 17 Supporting framework for hop cultivation. • Verticillium wilt • Red spider mite • Viruses: hop mosaic, hop latent, and

necrotic ringspot Cultivation practice varies widely, but a typical

schedule in Northern Europe is as follows:

Hop Breeding • March: Shallow plowing to reduce weeds, mulch in last years leaves and vines and Hops are dioecious plants i.e. they grow as add base fertiliser. male plants or female plants. Hop breeding • April: Stringing from overhead wires to takes the form of classic “crossing” of two rootstock. species, and growing out the hybrids. As such, • April/May: Training of new shoots onto all male hop plants are destroyed within a strings. three-mile radius of farms, to prevent • June: Plowing between rows for irrigation unwanted natural pollinations. Breeders are and weed control. currently trying to improve their strains in • July/August: Pest control as necessary. three main areas.

• August: Harvest. • Dwarf varieties • Hops should be harvested in all cases 10 days Disease resistance after ripening, to prevent overripe cones • High α-acid and β-acid varieties shattering. Historically, hop growing was extremely labour intensive, but with the By developing dwarf varieties, the tall technological revolution, harvesting has frameworks currently used can be eliminated. become almost fully automated. The These frameworks, although sturdy, can be harvesting steps are as follows: demolished by strong winds and are extremely expensive to repair and replace. In addition • The bines are cut down and transported dwarf varieties would allow easier, more to a picking machine, which strips the accessible and less expensive harvesting cones from the bine. coupled with a reduced labour requirement.

• The cones are separated, the debris Breeding varieties that produce higher α screened and removed. The picked hops concentrations of -acids (bitterness)

increases the yield per hectare dramatically. Caryophylene, Myrcene, Humulene and Farnesene As with cereal breeding, new hop varieties The four major components of the essential must be used on a pilot brewing scale to oils. Between them the oils account for about ensure the quality and application of the 60-80% of the essential oil of most varieties. variety. The amount of these constituents, and particularly the ratios between them, can be Glossary of Hop Terms used as clear varietal characteristics. These compounds are all highly volatile α-Acid hydrocarbons; and during boiling of the wort These are a major component of the soft – most, if not all of them, are driven off and so resins. When isomerised, these materials contribute little to hop flavour and aroma in provide the main bittering compounds beer. Some of the oxidation products of these associated with beer. The -acid content compounds, such as the humulene epoxides, varies widely amongst hop varieties from are thought to be positive contributors to levels of 3-4% w/w in aromatic type hops to beer flavour and hence sufficient ageing of levels of 10-14% w/w in the bitter hops. aromatic hop varieties is necessary to allow these products to he formed.

Aroma Much is spoken of the organoleptic quality Co-Humulone and intensity of dried hop aroma. These are The α-acid exists in three analogous forms, again strong varietal characteristics. There humulone, ad-humulone and co-humulone; does appear to be a general relationship and the properties of these analogues vary between the type and heaviness of a hop considerably with variety. Relatively high aroma and the flavour and aromatic levels of co-humulone produce a harsh, properties of a resultant beer. However, this unpleasant bitterness and have a negative relationship can be obscured by the manner impact on head retention. Although this of using the hops. A skilled, comparative belief is still being questioned, varieties with aromatic evaluation of samples of one variety relatively low co-humulone levels are still can detect those samples that have been strongly favoured picked too early or too late, over dried or stewed. Moreover, a trained evaluation can select particularly favourable growths of a Cone Structure variety from within the normal range of Certain physical properties of hop cones, aroma exhibited by that variety in a particular while relatively unimportant in the brewing season. process, are strongly characteristic of a

particular variety. For example, the cones of English Fuggle variety are markedly square in β-Acid cross section. Light loose cones are much Another soft resin component, the -acid, is more prone to shattering during harvesting not bitter in the natural or isomerised form. while heavy dense cones, like those of English Some of the oxidation products do provide Northdown pick beautifully as they roll well bitterness, and the -acid can be chemically and hang together. transformed into light-stable bittering forms.

Disease Reaction Different varieties can display a wide range of

reaction to various hop diseases. Of great importance in England is Verticillium Wilt and the fungal diseases Downy Mildew (caused by Packing Psuedoparonospora humuli) and Powdery Some varieties tend to shatter more than Mildew. others do when being packed. Growers can adjust practices to accommodate these peculiarities but the more difficult a variety Drying the more likely it is that mistakes will be Some varieties are more difficult to dry than made. others. Growers can adjust practices to accommodate these peculiarities but the more difficult a variety the more likely it is Pedigree that mistakes will be made. These are brief remarks about the ancestry of a variety. Modern varieties can often be traced back through two to three generations General Trade Perception of crosses often involving other known hop Over a number of years a hop variety will find varieties. It is important to note that the a particular role or niche within the brewing qualities of a hop variety are only partly industry and its particular properties will determined by the genes it receives. Of at become well known and accepted. This least equal importance is the selection for general perception is helpful to brewers particular characteristics practised by the hop considering the use of a variety new to them. breeders

Growth Habit Pickability Hop varieties vary widely in structural aspects This is another characteristic that is of direct such as general vigour, lateral (or side arm) concern to both grower and brewer. If a hop length, and the overall bine structure. These is known to pick well, one can expect a good characteristics can make a variety more or clean sample. If a hop is difficult to pick, one less easy to pick and handle. is more likely to see shattered cones and a higher proportion of leaf and stem in a sample. Lupulin Hop lupulin may vary in colour from pale yellow to an intense golden colour. It is not Storageability known if lupulin colour affects brewing Oxidation of -acid removes its ability to be performance but it is a fairly strong isomerised to the required bitter isomers. In characteristic of a variety. It is certain that comparable circumstances some varieties lose the bitter hops have much greater quantities a greater proportion of their -acid to of lupulin than the aromatic types. oxidation than others. Cold storage and anaerobic conditions can both delay oxidation, but the innate property of a variety Maturity in this context is important in commerce. This is a statement of the time in the hop Interestingly, some oxidation of essential oil harvest season at which the particular variety components is necessary to produce reaches optimal maturity. Harvesting in compounds thought to be important in beer England occurs from about the end of August flavours so controlled ageing is important for to the end of September. Of current English hops required for both bittering and aromatic varieties, the aromatic types tend to be earlier purposes. maturing than the bitter type varieties.

Total Oil  Total Soft Resins: Fraction of total α β This characteristic varies widely amongst resins soluble in hexane. ( - and - seasons, varieties and growths from 0.5 ml to acids, and *uncharacterised soft about 3.0 ml per 100 g of hops. Whilst the resins) soft resins are responsible for providing the  bitterness of a beer, the quantity and Hard Resins: The fraction of total composition of the essential oils are resins insoluble in hexane. (The responsible for the amount and quality of hop difference between the total resins flavour and aroma in beer. A brewer, when and total soft resins) deciding on which varieties and how much to use, will always consider the hops' * Uncharacterised fractions remain contribution to flavour and aroma as well as unidentified and have dubious brewing value. its bittering potential. This is the kilo dry weight of hops in zentners normally produced by that variety in commercial production in England. On average, the aromatic types tend to be lower yielding and hence more highly priced than the bitter types. As with other crops, yields vary markedly from farm to farm and year to year. Hence, the range in yields can be quite wide.

Zentner 1 Zentner = 50 kilos

Chemical Composition of Hop Constituents

Three fractions contribute the entire brewing value of hops:

• Total Resins • Essential Oils • Tannins

Total Resins The bittering Total Resins are subdivided and classified according to their varying solubilities in standard solvents.

 Total Resins: Characterised by solubility in diethyl ether and cold methanol. (Hard resins, α- and β- acids and *uncharacterised soft resins)

Tannins The β-Acids The Tannin fraction of hops devotes little The β-acids (Lupulones) have the basic character to beer and they are more chemical structure: detrimental than beneficial acting as haze precursors. They also promote the precipitation of protein-polyphenol haze complexes during wort boiling, aiding the formation of trub as hot and cold break.

The α- & β-Acids The α-acids (Humulones) have the basic structural formula:

Figure 18 The basic structural formula of the β-acids.

The β-acids, like the α-acids are composed of the parent phloroglucinol, differing only with the addition of the extra isopentyl side chain. The remaining structural groups are synthesised from amino acids as the hop grows.

Figure 19 The basic structural formula of the a-acids.

It is difficult to draw a single structure for the majority of hop resins, for they exhibit keto- Figure 20 Chemical structure of the amino acids Valine, Leucine and Isoleucine enol tautomerism. This is where the ketone and enol isomer forms of the compound exist Humulone and lupulone arise from leucine, in equilibrium with each other. The base unit, the co-analogues Phloroglucinol, the central parent of hop (i.e. co-humulone and co-lupulone) valine resins can be seen below demonstrating such and the ad-analogues a relationship. (i.e. ad-humulone and ad-lupulone) isoleucine.

Three analogues each exist for the α & β acids.

Figure 21 The chemical changes occurring during keto-enol tautomersim demonstrated with phloroglucinol.

essential oils confer aroma and are isolated for analysis by steam distillation. The oil components, a complex mixture of at least 300 compounds, range from 0.03-3% of the total hop weight, with seedless hops tending to contain elevated levels. The essential oils develop late during ripening, after the majority of the resins have been laid down.

The oil fraction can be divided into hydrocarbon and oxygenated fractions.

Figure 22 The differing side chains that make up the ad- and co- analogues of the α & β acids.

The α and β acids each account for approximately 50% of the soft resin fraction. Ad-humulone consistently forms 10-15% of the total α-acid fraction. Humulone and co-humulone concentrations fluctuate with variety, and can Figure 23 Structural diagrams of hydrocarbon compounds found in the be 20-50% and 45-70% of the total α-acid essential oil fraction. content, respectively.

The proportion of hop soft resin, the α acid : β acid ratio and the quantity of α and β acid analogues present, all differ with variety. Regional and seasonal differences and the presence of seeds further affect these relationships. Seedless hops have higher α- acid contents and therefore, greater bittering potential.

The Essential Oils

The Essential Oils comprise:

• hydrocarbons (various terpenes and their

derivatives) and, • oxygenated terpene forms.

In addition, to some extent the essential oils also contain fatty acids and esters. Whilst the Figure 24 Structural diagrams of oxygenated hydrocarbon compounds acidic resin fractions impart bitterness, the found in the essential oil fraction.

Myrcene (a monoterpene) is the most wort / beer temperature and pH, the α-acids abundant compound in the hydrocarbon are insoluble. For this reason hops are added fraction, which also contains humulene and during wort boiling. caryophyllene (sesquiterpenes). The hydrocarbons are extremely volatile and do During the boil, the α and β-acids not survive wort boiling. metamorphose to produce highly soluble products. These include the iso-α-acids, which KEYPOINT: Terpenes are compounds of the are the principal bittering compounds in wort chemical formula (C5H8)n, the majority of which and beer. occur in plants. The value n is used as a basis for classification. 1) Monoterpenes C10H16; The α-acid base unit consists of an 2) Sesquiterpenes C15H24; 3) Diterpenes C20H32. asymmetric carbon atom with a chiral centre All naturally occurring terpenes can be built up at C-6. Therefore, each analogue can exist in of isoprene units. two forms or enantiomers. These two forms exist as cis and trans isomers The oxygenated forms of the sesquiterpenes and terpenes, (predominantly acids, alcohols, KEYPOINT: The terms cis and trans refer to two esters and ethers) are less volatile and more forms of one isomer that differ only in their aromatic than the hydrocarbon. stereochemical arrangement. CIS- isomers have their functional groups adjacent or in the The essential oils generate the distinctive same plane across a bond; TRANS- isomers aroma associated with hops. The aromas are arrange with their functional groups in opposite characterised as either a dry hop or late hop planes either side of the bond. The five carbon aroma. The late hop aroma is produced when ring restricts rotation around these bonds and hop products are added to the wort during prevents the metamorphosis between the two copper/kettle boils, typically 10-15 minutes forms, hence the iso-α-acids form cis and trans before the wort is cast to the whirlpool. The isomers. late hop aroma is most likely derived from the oxygenated fraction of the oils. The Ideal conditions for isomerisation are: hydrocarbons are volatile and are lost during wort boiling, therefore, unlikely to contribute aroma. The hydrocarbon fraction will only • Slightly alkaline pH contribute character in dry hopped beers, o (@ pH 9 = 100% isomerisation) where whole hops are added to the finished o (@ pH 6 = 60% isomerisation) product. • The presence of divalent metal ion The formation of the hop characteristic does catalyst (e.g. Mg2+) not end with wort boiling. Modification continues throughout fermentation, with • Short, vigorous boil (≥ 60 minutes) esterification of acids and reduction of ketones. This is combined with the evaporation of hop compounds in the stream of fermentation gas and adsorption to the yeast surface.

α -Acid Isomerisation

Although the major bittering components of hops are the α-acids, bitterness is not provided in their discrete form. At normal

Figure 25 -Acid isomerisation to Iso-a-acids; Humulone into iso-humulone.

Processed Hop Products

The whole hop is bulky and therefore, an expensive product to transport and store. Hop Pellets Whole hops can be processed and transformed to reduce their size, whilst • Type 90 Standard hop pellets: comprise providing additional benefits including: whole hops, which after removal of debris are dried and hammer milled. The hop material can then be compressed into the • Increased bulk density/ decreased pellets and packaged. volume. • Improved convenience/ storage. • Type 45 pellets: enriched or concentrated. • Improved stability/ shelf life. The hop material is first fed through a • Increased utilisation. cutting mill and the waste fraction • Improved consistency/ homogeneity. removed before final hammer milling. • Easier, automatic addition. This process removes the majority of the • Reduced extract loss/ effluent. non-essential vegetative material, • Removal of unwanted elements (chemical enhancing the -acid content. residues/heavy metals). • Isomerised (iso) Hop Pellets: Isomerised hop pellets differ from type 90 in two Hop products today, commonly exist as ways. Firstly, magnesium oxide is added pellets or extracts. The diversity of hop to the hop powder prior to pelleting. products within these two groups is Secondly, during pelleting, the phenomenal. magnesium oxide reacts producing the salt of the -acids. The vacuum packed pellets are then stored at 50°C for

between 10 to 14 days. During this time using a hammer mill, which grinds with little the magnesium* salt of the -acid kinetic energy, so avoiding any temperature isomerises to the magnesium salt of the increases that could damage the hops. The iso--acid. fineness of the powder is determined by the moisture content of the hops and the size of *Magnesium and calcium are added to hop the sieves used in the mill. The powder is pellets; they act as catalysts increasingα -acid then placed in holding tanks before being solubility during wort boiling. pressed into pellets (pelletised) – further mixing occurs in these tanks. The majority of pelleted hops are added to the wort in the copper, during boiling. Some The hop powder then passes through a pellet aroma pellets can be added straight to the press and is pelletised. This increases the beer in cask or post fermentation for dry density of the hop powder and further hopping. improves space savings. It is essential that pelletisation occurs below 50oC – this helps By using pelleted hops, particularly pre- maintain the quality of the hops. Cool air is isomerised forms, then superior α-acid blown on the pellets to bring them to room utilisation and efficiencies can be achieved in temperature to prevent them from sticking the brewhouse, whilst retaining most, if not together. all of the original hop character. It is desirable to have uniform α-acid throughout batches of hop pellets, as this is Type 90 Standard hop pellets important for beer quality. The pellets are then packaged. Pellets are very oxygen A brief outline of the production process for sensitive as oxygen causes deterioration of Type 90 pellet is described in the following the hop oils and α-acids – so the pellets need section. to be packaged under a nitrogen-CO2 gas mixture.

Type 45 Pellets (Concentrated Pellets)

Figure 27 Production of Type 90 hop pellets.

Figure 26 Production of Type 45 pellets. The mixed hops are dried to the desired moisture content of 7-8% using a kiln at approximately 50oC. Before grinding, vine The production of Type 45 pellets is parts, leaves, clumps of earth, stones, wire essentially the same as Type 90 pellets except and other foreign materials are separated for a few additional steps. After separation of from the hops using magnets and a pneumatic foreign objects the hops are frozen in order to separator. harden the sticky hop resins. Once temperatures of -30oC to -40oC are reached The cleaned and dried hops are then ground then mechanical separation of the lupulin and

leaf fractions can proceed. • Pure oil extracts or emulsions. • Fractionated oil extracts. The deep frozen, brittle hops are crushed in a • Specialist reduced isomerised extracts. slowly revolving refrigerated crusher and then • Isomerised Kettle extracts or Post sieved into leaf and lupulin fractions. Cone Fermentation Bittering (PFB). shaped screw mixers are used to achieve a consistent powder blend before pelletisation. Hop extracts were traditionally prepared using solvents such as methylene chloride and trichloroethelyne. However, due to toxic Isomerised Hop Pellets residues left behind and general environmental issues, their use has ceased. Today ethanol and liquid CO2 are the two principal solvents used to completely dissolve and extract hop oils and resins.

Ethanol Extraction: A hop and 90% ethanol mix is wet milled and passed through a continuous multistage extractor. Alcohol flows counter-currently to the hop mix, becoming enriched with the hop constituents. The spent hops are separated from the resin liquid by a pressing process and then dried and pelletised.

The hop extract is concentrated as the alcohol is evaporated before a final steam scrub. The The pellets are made in the same way as evaporation system produces a concentrated regular pellets except for the following two hop extract composed of all the hop resins. steps:

1. Small quantities of food-grade Liquid CO2: magnesium oxide are added to the hop The hops (as pellets) are placed in an powder to catalyse the isomerisation extraction chamber. Liquid CO2 at extraction process. pressure is pumped through the extraction

vessel into which the hop components 2. The stabilised pellets are packaged, dissolve. The pressure in the vessel is reduced boxed and placed on pallets in a hot causing the CO2 to lose its ability to act as a room (50oC) until the isomerisation is solvent and is evaporated leaving the hop complete. Isomerisation in a hot room extract. Supercritical CO2 is also used with takes between 7 and 12 days, superior extraction properties (40-50°C / @ depending on the variety of the hop. 250 bar).

The CO2 gas is recovered and recycled for use Hop Extracts in further extraction runs. Hop extracts are principally purified solutions of particular hop components. They can be prepared to the brewers specification as:

• Pure resin extracts. • Oil rich extracts or emulsions.

Isomerised Extracts regular extracts which are normally in the range of 25-35%.

• Isomerised extract usage means lower transport and storage costs. Unopened containers can be stored at room temperature for a year with no loss in brewing value.

• The consistency of the product gives the brewer precise control over the bitterness levels.

KEYPOINT: Unlike the other hop extracts, pre- isomerised extracts do not require wort boiling to produce the iso-α-acids. As such, iso- extracts can be added directly to the beer for precise control of bittering both pre- and post- Figure 28 Production of Isomerised Hop Extract. fermentation, further improving utilisation.

Either supercritical or liquid CO2 extract can Hop Oil Extracts be used for further processing into isomerised Hop oil extracts or emulsions used to impart extract. To prepare the extract it is first aroma are produced through steam warmed and mixed with deaerated water distillation, allowing harvesting of the under an inert atmosphere (nitrogen gas). required fraction. Aroma emulsions provide The extract is further heated before the brewer with excellent control over the magnesium or potassium catalyst is added to intensity and consistency of dry-hopping induce isomerisation. effect.

After isomerisation is complete then a multi- step process is undertaken to separate the Reduced Iso-extracts iso-α-acid from the remaining hop material by pH reduction. The resulting isomerised Light in the range 300-500nm readily passes extract is standardised with de-ionized water through both clear and green bottles. Beer to an iso-α−acid content of exposed to this light quickly develops 20–30%. Non-isomerised hop materials are unpleasant off flavours, often described as recovered and run back through the plant for “skunky”. This is due to photolysis of the iso- α further production. -acids, which react to produce 3-methyl-2- butene-1-thiol (MBT) or isopentenyl Isomerised extract has various advantages, mercaptan (the skunky aroma). By reducing including: the iso-α-acids, through hydrogenation, photolysis, causing the development of • The product can be added at various skunky aromas can be prevented (Figure 29) stages of the brewing process. To achieve maximum utilisation the isomerised extract should be added after fermentation but before final filtration. The expected utilisation is approximately 95%, which compares favourably with the utilisation yields of hops, pellets and

Figure 30 The chemical structure of the three forms of reduced iso-a-acids.

Figure 32 Results of a 20 day beer test, evaluating the exposure to UV light of unhopped beer, beer with reduced iso-extract and beer Reduced iso-products have some draw containing pure iso-α-acid; mercaptan is an indicator of lightstruck backs. Isopentenyl mercaptan is flavour aroma. active at parts per trillion (ppt) and as such, even the smallest quantity of the light sensitive α-acids present in the beer, will The mechanism of the photolytic reaction is negate the effects of the reduced iso- shown below: products. This requires separate yeast handling or thorough acid washing (of the yeast) to clean and remove all hop particles. This must be combined with careful process management to avoid contamination with non-reduced products.

One of the most important hop characteristics is their anti-bacterial activity. If reduced PFB iso-products are the sole hopping agent in use, the wort will not be protected and is susceptible to microbial infection. This can be overcome by adding some of the reduced Figure 29 Chemical sights of iso-a-acid photolytic cleavage and its prevention. extract during wort boiling.

Light stability is not the only benefit derived It is reported that over-addition of the from the use of reduced iso--acids. reduced products generates a foam that Hydrogenating bond A benefits foam stability, appears artificial. whilst if either B1 or B2 is hydrogenated, light strike resistance is conferred.

The reduced forms of iso-α-acids are known as Tetrahydro-iso- α -acids, Rho-iso- α -acids and Hexahydro-iso- α -acids, reflecting the number of hydrogen atoms added (ie 4, 2 or 6 Figure 31 Reduced Isomerised Hop Extract Properties. respectively). These reduced compounds also

impart bitterness, but to differing degrees.

For example, tetrahydro- forms are more

bitter than α-acids, whilst hexahydro- forms

are comparable and rho-forms less bitter.

Analytical Assessment of Hops During the manufacture of hop products frequent samples are taken throughout the production process to test for correct procedures and quality. A few of these methods are described below.

Typically, hop product analyses are dependent upon the solubility of the hop resins in organic solvents. The initial extraction is made with benzene or toluene and subsequently diluted with methanol prior to analysis. Standard methods specify standard sampling, which Figure 33 Measurement of LCV by titration with acidified lead acetate. can vary depending if the sample is from unpressed hops, bales, pellets or extracts. Measurements must be made shortly after Customarily, 200 g samples are taken from a harvest to avoid the production of inaccurate random 10% of the product for analysis. LCV values from ageing hops. Older hops generate increased LCV’s, but lower than Historically, solvent fractionation of the total expected values of α-acids as predicted by the resins was sufficient, however, determination sensory evaluation of hop bitterness. This of the α-acid content identifies the brewing suggests that, although levels of α-acids have value of the hops more specifically. deteriorated, new bitter compounds are formed to replace the lost bitterness. α-acids hold three chemical properties upon However, one drawback of this method is that which contemporary analyses are founded. not all of the new compounds form lead salts.

• Formation of methanol insoluble lead salts. Ultra-violet Light Absorbance • Ultra-violet light (UV) absorption. The light absorption of the hop resins is • Optical rotation of polarised light. dependant upon the pH of the solution in which they are analysed; basic or acidic. From the absorption spectra, regression equations Lead Conductance Value (LCV) were derived. Optical density measurements With the addition of acetic acid acidified lead were compiled in basic solutions at: acetate solution to a methanolic hop extract, the α-acids present form a bright yellow • 325 nm = λmax for α-acids precipitate (the lead salt). This precipitate could simply be dried and weighed, but this is • 355 nm = λmax for β-acids clumsy and inaccurate. Alternatively, the lead acetate solution is slowly titrated into the hop • 275 nm = λmax for α and β-acids extract solution whilst the conductance or background absorption resistance of the solution is monitored. A graph of conductivity can then be plotted The concentration of both α and β-acids can against the volume of lead solution added. then be calculated from the regression The resulting curve, on extrapolation, allows equations: the determination of the reaction end point, or the lead conductance  Concentration α-acids = 73.79A325 − 51.56

A355 − 19.07 A275 value (LCV) of the hop extract. Although not exact, this LCV value gives a good estimate of α -acid content.

 Concentration β-acids = 55.57 A355 − 47.59 Polarimetric Analysis + A325 5.10 A275 The α-acids are the only important resin constituents demonstrating optical activity. The difficulty with this method is the preparation of a sample solution with sufficient opacity to light, allowing the refraction to be accurately recorded. Although polarimetric analyses are the most specific for α-acid determination, showing high levels of accuracy with fresh hops, they will give erroneous results with ageing hops and hop extracts and so are no longer used. The LCV is regarded as the most specific for brewing value.

High Pressure Liquid Chromatography (HPLC) is becoming the most reliable method of Figure 34 The absorption spectra for humuluone and lupulone in analysis. However, simple hand evaluation is acidic and basic solutions. still useful and can reveal much about product quality: colour, debris, infection, age, aroma etc. α β Alternatively, the and -acids can be measured separately, after HPLC (on reversed phase columns) by spectrophotometer. The Use of Hops in Brewing

Hop Utilisation Most of the bitterness contributed by the hops is derived from the

α-acids when they are isomerised during wort Spectrophotometric methods are also used to boiling. Isomerisation of α-acids during the generate identifiable bitterness boil is never 100% efficient and is dependent measurements in relation to the actual upon the following factors. sensory bitterness of beer, and not simply -

acid content. The recommended EBC analysis states 10 ml of acidified beer is extracted with Duration of the boil 20 ml of To impart bitterness the typical 45-60 minute boil is usually sufficient to allow complete iso-octane. After centrifugation the bitterness isomerisation, but reduced boiling will be of the beer is read against a blank of pure iso- inefficient. octane. Addition of the hops to the boil to impart aroma should be left to the later stages (approximately 15-20 minutes before boiling ceases). If hops are added early in the boil the volatile oil components will be lost. Leave it too late, however, and -acid isomerisation may not complete. To overcome this some of Figure 35 The correlation between organoleptic sensed hop the hops can be added at the start of the boil strength and BU measured by spectrophotometry. and the remainder towards the end.

Boil temperature As well as the losses described above, hop Any chemical reaction proceeds quicker with material is lost throughout fermentation and clarification due to: increased temperature. As such the α-acid

isomerisation can be accelerated using a high • pressure boil. Scrubbing action of CO2 (hop oils only). • Adsorption of constituents onto the yeast cell surface (top fermenting yeasts are Wort pH worse than bottom fermenting yeasts). • Adsorption onto filter material. Isomerisation and solubility is greatest at high

pH. An alkaline pH reduces hop losses, which

can take the form of hop precipitates lost as Hop utilisation is improved by using pre- trub. As the pH of the boiling wort falls so to isomerised pellets and post fermentation α does the formation of the iso- -acids. extracts.

Hop rate The greater the amount of α-acid used in hopping, the more losses are enhanced. For example, the more α-acid present the more iso-α-acid is formed, but the percentage conversion is less.

Wort gravity Figure 36 Bitterness factor and % utilisation for different hop preparations. Hop utilisation is most efficient in lower gravity worts and least productive in more KEYPOINT: CO2 Scrubbing is the process concentrated worts. whereby highly soluble, volatile compounds are extracted into the CO2 produced during The efficiency of α-acid conversion to the iso- fermentation as it rises through the wort, α-acids, or the hop utilisation is expressed as: removing the compounds from the beer.

Calculating a Hop Grist

In order to calculate the weight of hops required to produce a beer with a required Hop utilisation is notoriously poor. Often hop level of bitterness it is necessary to know the utilisation calculations return values of around following information: 30%; 40% hop utilisation is an acceptable numeration. Pre-isomerised products suffer • Bitterness of beer required in IBU. lower losses than • The % α-acid in the hop material used. un-isomerised, whilst post fermentation • % utilisation of the hop material. bittering (PFB) products can achieve 95% utilisation.

KEYPOINT: 1 IBU (International Bitterness Unit) is usually assumed to be equivalent to 1 milligram of iso-alpha acid in 1 litre of water or beer.

Example

A brewer needs to produce a 100 hl of beer containing 26 IBU, with bitterness contribution from a hop variety with a 10% -acid content. What weight of hops (kg) does the brewer need to use?

You will need the following information:

. Volume (litres) = 100 x 100 = 10,000. . 1 IBU = 1 mg/ litre. . Total IBU in 10,000 litres beer = 26 x 10,000 = 26,000 IBU. Figure 37 The oxidation of the α and β-acids to produce the bitter . 260,000 IBU = 260,000 mg (or 260 g)of iso- compounds Humulinones and Hulupones respectively. -acid in the final beer.

If hop utilisation is only 25% (i.e. only 25% of Some compounds such as humulinic acid, the original α-acid ends up as iso-α-acid in the generated through the hydrolysis of iso-α- final beer), then the brewer needs to supply acids, are not bitter at all. (100/25) x 260 = 1040 g of α -acid.

So, the total weight of α -acid needed to produce 100 hl of beer with a bitterness of 26 IBU is 1.040 kg of α -acid.

Considering all the α -acid comes from the hop variety with 10% α -acid, then the weight of hops required will be: Figure 38 The hydrolysis of iso-a-acids to produce the non-bittering compound Humulinic acid. 1.040 x (100/10) = 10.4 kg Further reactions occur during storage to the detriment of hop quality. The α-acid content is diluted in a linear fashion when plotted Other Compounds against time, and the concentration of essential oils decreases almost as fast. The Beer bitterness is not only derived from the reactions mainly involve oxidation reactions, α iso- -acids. Bittering components can also be but others have been implicated. derived from the oxidation of the Deterioration of hop material is accelerated α β and -acids, or even from the reaction with exposure to air, moisture and elevated products of iso-α-acids. Some of these latter temperatures. If stored at 50°C, losses can compounds are in fact, more bitter than equate to 50%, within one year. Therefore, iso-α-acids (e.g. anti-isohumulones and whole/leaf hops should be stored alloisohumulones). Hulupones derived from compressed, in vacuum containers (but this the oxidation of the β-acids are as bitter as doesn’t occur in commercial practice) and for iso-compounds and account for as little time as possible at temperatures as approximately 10% of the bitterness provided cool possible. by hops. The result of hop deterioration through the

oxidation and polymerisation of the α- and β- fermentation, to the maturation vessel or to acids is the generation of a rancid, cheesy the cask to give beer a dry hop flavour - this is aroma. These cheesy aromas are imparted by often described as resinous, spicy and citrus. free acids, originating from the oxidation of As the α-acids are only slightly soluble in cold the acyl side chain, of the acidic resin beer, there is hardly any increase in the fractions. Thus the main culprits are bitterness of beer with dry hopping. isobutyric, isovaleric and 2-methyl butyric acid. In addition, ethyl esters consequently Hops produce up to 3% of essential oils during formed from these acids contribute to a stale the later stages of ripening after the bulk of hop aroma. the resin synthesis is complete. The composition of the oil reflects not only the variety but also the degree of ripeness.

Over 300 hop oil compounds have been isolated and they are usually separated and identified using gas chromatography with mass spectroscopy (GCMS). The details for these compounds are covered in detail in section 1.6.2.

The essential oils can be divided into three classes: Figure 39 The oxidation of the α and β-acids to produce the stale, “off flavoured” cheesy aromas imparted by free acids. • Hydrocarbons • Oxygenated compounds • Sulfur Compounds

Hop Aroma The essential oils in hops are the source of Giving a hop aroma character to a beer not aroma compounds. These oils are volatile and only requires selecting an appropriate hop will be almost entirely vaporised from the variety to provide the essential oils but also to kettle if they are present from the start of a add the hops so that at an appropriate stage 60–90 minute boil, although some will be in the process. These stages can be divided converted by heat or chemical reaction. To into the following: compensate for this, many brewers who want beer with a hoppy character add selected • Kettle hops aroma varieties into the kettle between 5 and • Late hop addition 20 minutes before the end of the boil. This • Dry hopping gives sufficient time to extract the hop aroma but ensures that all the oil is not lost in the vapour. Kettle Hops When hops are added at the beginning of the Late hop character is often described as floral kettle boil, little if any aromatic oils persist or citrus, but it can be unpleasant if present in into the finished beer. There will be some too high a concentration. The variety of hop, chemical modification or combination of the timing of the addition, as well as the flavour compounds. kettle shape and the material of construction all have a major influence on the subtlety of the final beer aroma. Late hop addition

Hops may be added at any stage from 20 to 5 Hops can also be added to beer after minutes before the end of the boil, or fresh

hops added to a hop back to allow sufficient time for the extraction of some of the hop oils without all being lost due to vaporisation. Not only will some of the more volatile hop oils be lost in the last few minutes of boiling or while waiting for wort cooling, but also the remaining oils may be modified or lost during fermentation. It is usually the heavier esters and ketones that are retained to give the fruit citrus characters found in many late hop lagers. The extent to which these characters persist depends on the kettle design as well as the hop variety.

Dry Hopping Appropriate hop varieties may be added during maturation or to cask to impart a hop aroma and taste particularly to traditional ales. A wider range of hop oils is extracted than during late hopping, which imparts a floral fragrant note to beer often with spicy characters that can be astringent if overdone. When whole hops are added to a cask the extraction and chemical reaction of the oils will continue throughout the drinking life of the cask which produces a constantly evolving change in palate over time.

Self-Assessment Questions

The following questions are a mixture of true or false, multiple choice and standard questions. We are going to try and catch you out so think carefully about all of the questions, good luck!

1) Hop α-acids provides the bitterness associated with beer. True/False?

2) It is the chiral centre at carbon 6 of the phloroglucinol unit that allows the production of the cis- and trans- enantiomers of the α-acids. True/False?

3) Which of the following would you identify as ideal conditions for α-acid isomerisation?

a) Slightly acidic, pH 5 b) Slightly alkaline, pH 6 c) Alkaline, pH 9 d) The presence of Ca2+ ions e) The presence of K+ ions f) A 35 min boil at 110°C + agitation g) A 65 min boil at 100°C + agitation h) A 80 min boil at 90°C

Is it possible to achieve these conditions during normal production? Explain your reasoning.

4) Draw the chemical structure of co-humulone and its isomerised product, iso-co-humulone.

5) The greater the amount of hops added to wort the greater the hop utilisation. True/False?

6) Hop utilisation is greatest in lower gravity worts. True/False?

7) During production, the final beer produced has a lower bitterness value than expected, even though a hop utilisation of 40% in the brewhouse was accounted for. Give reasons for this anomaly.

8) A 10 ml sample of acidified beer (at a 1:9 dilution with water) is extracted with 20 ml of 2,2,4 trimethylpentane. This sample is then analysed spectrophotometrically at a wavelength of 275 nm, against a blank of pure 2,2,4 trimethylpentane. The beer returns an absorbance value of 0.065. What is the bitterness of the beer in BU’s? Is it

a) 32.0 b) 32.5 c) 33.25 d) 325.0 e) none of the above

9) Hand evaluation of fresh hops is a redundant, inaccurate method for determining hop quality. True/False?

10) Arrange the following in order of utilisation efficiency, from greatest through to the least.

a) Iso hop pellets b) Type 90 hop pellets c) PFB extracts d) Type 45 hop pellets e) Iso kettle extracts

11) A beer has been manufactured using a mixture of isomerised pellets added during wort boiling and reduced iso extracts, added post filtration. Into which colour can and bottle should the beer be packaged to achieve the greatest shelf life?

a) Blue bottle b) Clear bottle c) Red can d) Green can e) Green bottle f) Brown bottle

12) Draw the structures of three reduced iso compounds and state, which gives the best foam enhancement, light stability, and list their relative relative bitterness’ to iso-α-acid.

Self-Assessment Answers

1) FALSE: Although the acidic resin fractions of hops comprise the bittering components (these are primarily the α-acids) it is the isomerised form (the iso-α-acids) that provide beer with its bitterness.

2) TRUE: It is the unsymmetrical nature of the six carbon ring that allows the formation of cis- and trans- isomers, i.e. when one isomers mirror image cannot be superimposed upon itself.

3) C, D, and G are the ideal options.

a) pH 5 is too acidic and will hinder solubilisation and isomerisation of the α-acids. b) pH 6 is too alkaline and there is only approximately 60% conversion. e) Potassium (K+) is not a divalent metal ion and will not catalyse the isomerisation, unlike Ca2+, although magnesium is the most suited. f) Although 35 min at 110°C with agitation may seem to be equal to 55 min at 110°C with agitation, 35 min is too short for trub formation as well as isomerisation. Whilst the energy costs of maintaining the boil at 110°C are also a hindrance combined with the potential for extra colour formation. g) 80 min at 90°C is too long and at too low a temperature, colour formation will be high and all aroma will be lost. Without agitation trub formation and hop utilisation will be poor.

Of the three ideal answers only c) cannot be achieved during wort boiling. Wort pH ranges between approximately pH 5.5 (at mashing) through to pH 5.2 (prior to fermentation). A wort at pH9 would be incredibly difficult to achieve would be detriment to the process as a whole. pH 5.5 is the ideal for enzyme activity during mashing, and after wort boiling, a highly alkaline pH would completely kill yeast activity. 4)

cohumulone isocohumulone

5) FALSE: Try to remember hop utilisation is never 100% efficient, therefore if more hopping material is added the greater the loss will be enhanced.

6) TRUE: Greater hop utilisation is achieved in weaker worts. This is most likely attributable to the increased solubility of the hop components in the more aqueous environment.

7) The rate of hop addition during the copper boil is always corrected to compensate for the losses attributed to inefficient utilisation. However, losses also arise during downstream processing, especially during fermentation. The hydrophobic nature of hops encourages them to escape aqueous environments at any possible opportunity, which impacts upon utilisation figures further. Iso-acid levels are dissipated, left behind on vessel surfaces when foaming removes hop materials from the wort. Similarly, hop materials are adsorbed onto the yeast cell surface, and removed from the wort at cropping. Bittering materials are further removed from the wort, extracted by the scrubbing action of CO2 as it rises through the vessel. Final losses are incurred during beer filtration as bittering materials are adsorbed onto filter bed particulates. To this end, the addition of bitterness would be most efficiently achieved in the form of pre-isomerised extracts, added post-filtration.

8) ANSWER = b) 32.5

Bitterness units (BU) = A275 x 50

Therefore 0.065 x 10 (the dilution factor) = 0.65

Therefore 0.65 x 50 (the conversion factor) = 32.5

Therefore the bitterness of the beer is described as 32.5 BU’s

9) FALSE: Hand evaluation of whole/baled hops can be a rapid, meaningful tool in determining hop quality. Fresh hops should be free from brown tainting (oxidation), and extremely aromatic. This is observed best by rubbing the hops between your hands. This should produce a sticky bright green mass, with a pungent, fruity hop aroma. Visual, hand evaluation also allows the identification of excess debris (string, stones etc.) and any infection (moulds, viruses, and pests).

10) Greatest hop utilisation:

PFB extracts: pre-isomerised extracts, added post fermentation, (ideally post filtration) incur no losses and imparted bitterness is proportional to levels of extract added.

Iso-kettle extracts: should incur no losses in the brewhouse through isomerisation but some bittering material will be lost, removed with the trub. Remaining losses are comparative to other materials down stream.

Iso-hop pellets: will incur slightly higher losses than the kettle extract with reduced efficiencies attributable to the effectiveness of pellet solubilisation.

Type 45 pellets: effect greater losses than the above iso-pellets due to the need for isomerisation. However the hop material is more concentrated than the Type 90 pellets and therefore experience greater efficiencies.

Worst hop utilisation:

Type 90 pellets: experience the worst utilisation due to the increased difficulty in extracting the bittering components during boiling (solubilisation) combined with losses associated with isomerisation.

11) A trick question for two reasons. If the beer is to be packaged in a can, the colour is inconsequential as the beer is at no risk of photo-oxidation (light will not penetrate the can). Don’t be tempted to think that because the beer contains reduced iso-products it is automatically protected from sun strike, and can therefore, be packaged in any coloured bottle. Here there are two concerns. First, there is a mixture of hop products within the beer. Reduced iso products only afford sunstrike protection when they are the sole hopping agents. When unreduced hop material is present (even at ppm levels) this can be oxidised to generate isopentenyl mercaptan, the "skunky" flavour. Also beer staling is not only concerned with hop material. Sunlight will also promote the production of hazes and off- flavours through oxidation. Therefore, bottles, where marketing will allow, should always be brown or amber (never clear or green) to prevent exposure of the beer to sunlight.

12)

HEXAHYDRO TETRAHYDRO RHO

The Institute of Brewing and Distilling www.ibd.org.uk