l BASICS OF SPIRIT PRODUCTION iStock.com/NevaF sition and organoleptically by some form of flavour profile. They will have a Batch distillation full understanding of how the desired flavour profile can be impacted by raw material choice, mashing processes, The pot still process yeast selection and fermentation – and most importantly for this article – how By Billy Mitchell distillation delivers their products. For those entering the spirits indus- try this knowledge will not be generally This is the fifth in a series of articles to support those available from previous experiences studying for the General Certificate in Distilling. Having and thus they will have to revert to first principles during the overall design of already covered the specification, purchase and storage their plant – this may have some risks of raw materials in article one, through the various to final product quality but these can be conversion and mashing processes in articles two and managed during commissioning and early production activities. three into article four on yeast and fermentation, we are now in a position to gain a greater understanding Pot distillation The development of the typical pot still of how distillation delivers our products. I will cover has taken place over many hundreds batch distillation in this article followed by continuous of years. History has shown earliest distillation taking place in ceramic distillation in article six. or glass pots heated directly in open furnaces or hearths with air-cooled his article will cover the theory, Mature spirits businesses will al- condensers used to recover the distil- Tprinciples and practicalities and ready have well-established processes late. The importance of copper in general risks associated with malt for the manufacture of their spirit controlling spirit character was not whisky distillation processes in Scot- products. These will include a thorough fully recognised at the time – the metal land – although they will be equally knowledge and understanding of their became the material of choice due to relevant for all spirits produced from raw materials, how they are processed its heat conductivity and ease of form- this batch process, even though the through mashing and fermentation and ing into the now-familiar pot design. input raw materials and subsequent the desired character of their prod- The theory of distillation has not fermented wash composition may be ucts. The spirit character will be well changed over the years although its markedly different. defined in terms of analytical compo- impact on spirit composition and char- 44 z Brewer and Distiller International April 2017 www.ibd.org.uk BASICS OF SPIRIT PRODUCTION l iStock.com/ DenisDubrovin One example of the batch pot still process acter is now more widely understood batch process. These may include: pressure at normal temperature is due to huge developments in analytical Fermented wash, wash charger, described as a low volatile compound. methodology giving the ability to meas- low wines, foreshots, sprit cut, spirit The vapour pressure of a liquid ure a huge number of compounds at safe, feints, pot ale, spent lees, lyne increases as the temperature is raised very low concentrations. This learning arm, swan neck, still shoulders, puri- until it reaches the applied pressure at is by no means fully exhausted and will fier, condenser, worm and worm tub, which point it will boil. Different liquids develop further as the understanding of cooling water supply, reflux, steam exert different vapour pressures and this complex science continues. pan, steam coil, internal heat source, thus boil at different temperatures; the The main distillation plant is likely external heat source, balance still composition of the vapour originating to consist of a wash charger, wash and operation, unbalanced still opera- from a liquid mixture will not contain spirit stills and associated condensing tion, spirit receivers, pressure relief components at the same concentration systems, valves, pipe work and various systems, anti vacuum systems, spirit of the liquid. The concentration differ- spirit and feints receivers to collect the charge, charge strength along with ence between the two phases allows different condensed liquids into low many more. for separation of the components and wines, foreshots and spirit. It will also Some of these will be discussed in this is the basis for all distillation. include the provision of thermal energy article. Distillation involves partial evapo- to drive the distillation processes in ration of the liquid followed by con- conjunction with integrated heat and Distillation theory densation of the vapour. The resulting energy recovery processes along with Distillation is a process for separat- condensate is enriched in the more some form of vapour cooling process. ing the component substances in a volatile components thus the starting The feed material for the first distil- liquid mixture by evaporation and liquid mixture is separated into two lation is fermented wash from fermenta- condensation. This process utilises fractions with different compositions. tion – the feed for the second distillation the differences in volatility in the Fermented wash from an all-malt will include the low wines from the wash mixture of components to produce mash contains many compounds or distillation and feints and foreshots from either complete or partial separation congeners – they will distil to different previous spirit distillations. The inter- which increases the concentration of degrees depending on their volatility. nals of the wash distillation can and do selected components. Distillation is To understand distillation theory it is become fouled with organic solids from a common process employed across more practical to consider a simple the fermented wash – the spirit still does many industries worldwide and is of two-component mixture of water with not suffer from this fouling although course vitally important to the spirits ethyl alcohol. cleaning procedures must be provided industry. Unlike many of the processes Water boils at 100° C at atmos- for both stills. involved in pre-distillation, distillation pheric pressure while ethyl alcohol The control of all these processes is a physical separation methodology boils at 78°C - from this it can be can be totally manually, semi-auto- and not a chemical reaction. deduced ethyl alcohol is preferentially mated or fully automated. Vapour pressure is defined as the distilled when heating a mixture. The Needless to say there is no one pressure exerted by a vapour in ther- batch distillation process employed in design or scale of plant used – this is modynamic equilibrium with its con- malt distilling can be described by fol- very similar to the plant configuration densed phase at a given temperature lowing the diagram below which shows in the pre-distillation operations – this and pressure in a closed system. The the relationship between vapour and is one of the joys for those enthusi- normal boiling point of a liquid is the liquid at equilibrium for different ethyl asts who thrive on these variations in temperature at which the vapour pres- alcohol strengths – the temperature at plant design and operation and try to sure equals the ambient atmospheric which the liquid mixture boils is given establish the potential impact of these pressure. A substance with a high va- on the Y axis. on final spirit character. pour pressure at normal temperature Fermented wash at approximately There is also another list of ter- is often referred to as volatile. Con- 8% v/v ethanol (Point A) will boil at minologies specifically aligned to this versely a substance with a low vapour around 94.5°C (Point B) giving off www.ibd.org.uk Brewer and Distiller International April 2017 z 45 l BASICS OF SPIRIT PRODUCTION be to use a two-stage distillation pro- In extreme circumstances wash 100 cess with the final product recovered stills can froth over – the effect of en- between 63-70% v/v ethanol. trainment is to reduce the alcohol con- centration of the product and possibly B C Continuous operation carry over undesirable compounds not To produce a product similar to grain normally distilled and recovered. whisky at around 94% v/v ethanol would require a large number of pot The distillation process 90 Vapour still distillations. To achieve this in a For those that are new to the spirits more economical and practical man- industry it could be argued that the ner, continuous distillation such as distillation process to produce malt spirit Temperature (˚C) Temperature that used in the operation of a Coffey is a simple one. The wash still separates still is used – this will be covered in a the alcohol with some water from the Liquid separate article on continuous distilla- residual yeast, unfermented suspended tion. There are some distillers who use solids from the mashing process creat- 80 a three-stage batch pot still process. ing low wines as the distillate and pot ale wash 8% wash This triple distillation technique is as the residue left in the pot still after low wines 45% generally seen as the ‘norm’ for Irish distillation. Any and all volatile com- A D E whiskey. pounds including ethyl alcohol should be 0 50 100 Ethanol concentration (%V/V) There are two other theoretical recovered in the low wines. aspects related to this batch pot still The spirit still is charged with these distillation which should be under- low wines and recycled feints and Ethanol/water equilibrium stood, namely reflux and entrainment. foreshots from previous spirit runs and vapour at the same temperature (Point Reflux is the term used to describe produces a distillate which comprises C) at a strength of 45% v/v ethanol any material returning to the original another three distinct cuts of foreshots, (Point D) This is the first stage in the liquid, condensed from its vapour. This spirit cut and feints. The residue left wash distillation and the condensed increases the liquid ethanol strength in the spirit still, basically water, is vapour is the first running of the low and consequently the vapour alcohol discharged as spent lees for further wines.