2/25/2014
Chemistry of Juice & Wine
We will begin with the composition of must/grape juice and then cover the Wine Chemistry composition of wine. Constituents are covered in highest to lowest Wine 3 concentrations. Introduction to Enology
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Tonight: Exam # 1 Old English Money vs. US Use Scantron and #2 Pencil Leave one empty seat between you and your 2 farthings = 1 halfpenny neighbor. 2 halfpence = 1 penny (1d) 3 pence = 1 thruppence (3d) All backpacks, bags, and notebooks on floor. 6 pence = 1 sixpence (a 'tanner') 12 pence = 1 shilling (a bob) OR 100 pennies = 1 Dollar You will have 20 minutes to complete the test. 2 shillings = 1 florin ( a 'two bob bit') When your finished hand in your test face down 2 shillings and 6 pence = 1 half crown by section and wait quietly at your desk or 5 shillings = 1 Crown 20 shillings = 1 Pound outside the classroom. Write name on both Scantron & Test
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Tonight's Lecture Metric System
Wine chemistry The preferred method of measurement world Juice composition wide (except for the US, Burma & Liberia) Acid and sugar adjustments Look over handout and get comfortable with Wine composition converting US to Metric & vice versa. Units change by factors of 10 Use the handout on conversions of a website to help you out.
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Wine Chemistry 1 2/25/2014
Metric Units Composition of Must
Water, 70 to 80%, the sweeter the grapes, the lower the % of water. Most important role is as a solution in which all other reactions take place. Sugars, 15 to 35%, they are about 90% of the soluble solids or extract in the juice.
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Some definitions: Soluble: A substance that can be dissolved, sugar being dissolved in water is an example. Insoluble substances do not dissolve, an example would be mixing sand into water. Precipitate: A substance that comes out of solution in a liquid and reverts to its solid form. Suspended Solids: Solids suspended in the solution that have not settled.
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Sugars (carbohydrates) Metric System The primary sugars are glucose and fructose in about equal amounts. These sugars are both Winey laboratories use the metric system. hexoses (6 carbons) have the same formula
European made wine equipment use metric C6H12O6 but different structures. units. Most problems occur when converting between US system and metric system. NASA lost $125,000,000 Mars spacecraft to due incorrect conversion.
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Wine Chemistry 2 2/25/2014
Molecules Containing Carbon Unfermentable sugars
Remember from our chemistry review that the Yeast do not have the ability to consume corners of the hexagon represent carbon atoms. ferment every type of sugar. Very small amounts of residual sugar remain in all dry wines due to unfermentable sugars Carbon atoms that are present (mostly pentoses). are at the comers of the hexagon
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Molecules Containing Carbon Measuring Sugars Sugars can be measured directly in the lab Remember from our chemistry review that the through analysis. This is how low levels of corners of the hexagon represent carbon atoms. sugar in finished wines are measured. An oxygen atom Sugars make up a very large percentage of the makes up one juice before fermentation so it is much easier comer of the to measure the sugar by density. hexagon
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Sugars Measuring Sugars Sucrose (table sugar) is a molecule that combines one Degrees Brix (sometimes called balling) is molecule of glucose and one how sugar is represented as a density molecule of fructose. It is measurement. present in native American 1 degree Brix (B) = (% by weight) = 1 gram grape varieties like Concord of sugar per 100 grams solution (water & up to about 25%. Not a lot sugar combined). in Vinifera. Yeast can ferment sucrose.
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Wine Chemistry 3 2/25/2014
Example ~ Brix Standard Specific Gravity
Specific gravity is useful when buying or To make a 20 ºBrix solution for calibrating a refractometer mix: selling bulk wine. 20 Grams of sugar Wine is usually sold by the gallon, however 80 Grams of water (80 ml) the amount of gallons will increase or decrease based on a wines temperature. 100 Grams total solution weight So when selling wine it is best to determine the amount of gallons by weight which is constant.
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Other Units for Measuring Sugars Specific Gravity The specific gravity of water in U.S. units is Units of sugar measurement are different # outside of the United States. 8.328 /Gallon, so if the net weight of the wine on the truck is 42,360# then how many gallons Baumé , this method is popular in Europe are there on the truck? Brix = Baumé x 0.55 # Weight (SG x 8.328 /Gallon ) = Gallons Baume is an convenient method because the degrees Baumé approximates what the So # alcohol will be if the juice is fermented dry. 42,360# (0.990 x 8.328 /Gallon ) = 5,138 Gal. 13.5ºBauméferments to about 13.5%Alcohol Why was the specific gravity < 1.0? 20 23
Other Units for Measuring Sugars Methods of Sugar Measurement
In brewing specific gravity is the preferred Refractometers: Easy to use and usually method of measuring sugar. more accurate than hydrometers. The changing density of a liquid changes the Using specific gravity sugar expressed as refraction (bending of light passing through density in grams/ml, water by definition has a it) measures dissolved solids. SG of 1.000 1° Brix = SG of 1.004 20° Brix = SG of 1.083
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Wine Chemistry 4 2/25/2014
Methods of Sugar Measurement Methods of Sugar Measurement Hydrometers: Not quite as easy to use but Refractometers Cont. relatively cheap, measures the weight of a Problems: Expensive, delicate instruments, solution by displacement. Can be used alcohol affects refraction, so they cannot be during fermentation but the lower density of used during fermentation. Temperature also alcohol effects the Brix reading. affects refraction so it must be temperature Will read negative at the end of fermentation compensated. because alcohol has lower density than water.
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Optical Refractometer Methods of Sugar Measurement Most hydrometers are calibrated to 60 F or 20 C (68F), so they need to be temperature compensated. The more accurate, the more expensive and delicate. Several hydrometers with different ranges give better accuracy.
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Methods of Sugar Measurement Digital Refractometers
Recently portable digital refractometers have Hydrometers can also give false readings by the become more affordable and more popular. presence of suspended solids or gas bubbles. Some hydrometers have internal thermometers Water resistant, for compensation. not waterproof! Using clarified juice reduces error from suspended solids. Spinning the hydrometer dislodges bubbles.
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Wine Chemistry 5 2/25/2014
Hydrometers Adjusting Sugar The sugar left in the wine after fermentation is called the Residual Sugar or RS When adding sucrose the Brix or RS can be added by gm/L to the desired level.
To add 0.5 grams/Liter to 60 gallons of wine: 60 Gal x 3.78 L/Gal =228 Liters 228 Liters x 0.5 Grams/Liter = 114 grams
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Methods of Sugar Measurement Adjusting sugar with sweet wine or juice Digital Density To sweeten a must or wine with sweet juice or Meters More wine is simple algebra by using the principle that accurate and easy to the sum of the concentration times volume of each use, they are wine being blended will be equal the concentration definitely worth the times volume of the final wine. investment for commercial wineries.
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Adjusting Sugar Example To adjust 10,000 Gallons of dry wine 0.1% RS Illegal to add to wines in CA. except for to 0.4% RS how much juice at 10% RS do you sparkling wine dosage, but it can be added as add? grape juice or grape juice concentrate. Let X = Gallons of sweet wine to add With homemade wines and wines made outside of California, sucrose (table sugar) (10,000 + X) .4% = {(10,000) (.1%)} + X(10%) can be used for adjusting the sugar level 4000 + .4X = 1000 + 10X before or after fermentation. 3000 = 9.6X Adding sugar does not increase ripeness 312.5 = X (flavor). 33 36
Wine Chemistry 6 2/25/2014
Titratable Acidity TA Acids Present in Juice TA is determined by titration with a base to Juice and wine are dilute acid solutions. The an endpoint of pH 8.2 (phenolphthalein) it is acidic nature of wine has a profound affect then expressed as grams/100ml or on the sensory qualities of wine, microbial grams/liter (g/L) of tartaric acid. stability, color, protein (heat) stability, and Example 8.9 g/L = 0.89g/100ml tartrate (cold) stability. In France TA is expressed as grams of sulfuric acid/Liter g/L tartaric acid X 0.65 = g/L sulfuric acid.
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Principal Acids in Juice Titration
Malic acid Tartaric acid Citric acid When performing a the endpoint of 8.2
COO- + H+ pH is just as the solution turns pink. | The endpoint can be difficult to see in COO- + H+ COO- + H+ CH2 | | | red wines. HCH HC-OH HO-C-COO- + H+ | | | HO-CH HC-OH CH2 | | | COO- + H+ COO- + H+ COO- + H+
Disassociated Carboxylic acid groups Before At Endpoint Too Far!
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Principal Acids in Juice Acids Tartaric and malic make up over 90% of grape You can add tartaric, malic, citric, or lactic. For most adjustments tartaric acid is used juice acid. Tartaric acid is rarely found in other because it disassociates best (lowers the pH fruits. Other acids are: lactic, is present in more/gram) and is microbially stable. small amounts in juice, ascorbic (vitamin C), Other acids taste different than tartaric and fumaric, pyruvic and many more. have different affects on perceived acidity. Titratable Acidity (TA) Measures the sum of Since TA (Titratable Acidity) is measured as hydrogen ions free or attached; it does not gm/L Tartaric acid, 1g/L citric will not raise measure the total acidity (all acid anions). TA 1 g/L.
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Wine Chemistry 7 2/25/2014
Acids in Wine Adding Acid The earlier the acid is added the better it will harmonize with the wines flavor. Pre- fermentation is best. Since wine is a buffer the amount of pH shift you get per gm/L varies but a good approximation is: 1 gm/L tartaric addition lowers pH by about 0.1
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Adding Acid High pH + High TA Wines Very easy using the metric system, A common problem in red wines made from 1 gm/L addition tartaric acid raises TA 1 gm/L high Brix grapes is high pH and high TA. To raise the TA 1 gm/L of 100 Gal. wine This is because of the high potassium content (1 gm/L) (3.785 L/Gal.) (100 Gal.) = 378.5 gm in the juice. In English (American) units: The pH is too high but the wine tastes sour. Approximately 8.3 #/1000 Gal. = 1 gm/L Best to adjust the wine to the proper pH before ageing and then de acidify if needed (usually it’s not) before bottling.
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Adding Acid Adjusting Acid before Aging Acid can be mixed with juice wine or water. Hot water works well but gives off more Ballpark numbers, fumes. Try to keep reds pH<3.70
Never mix acid and SO2 in the same bucket, Try to keep whites pH<3.40 the low pH will release lots of SO2. When adding acid it is never a bad idea to perform bench trial first for taste and analysis for pH shift.
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Wine Chemistry 8 2/25/2014
Potassium Bitartrate Potassium Bitartrate
KHTa, potassium bitartrate, also called Potassium bitartrate is important in wine cream of tartar. stability and we will learn more about it in the Potassium bitartrate is not completely soluble wine processing lecture. in juice or wine. Solubility is influenced by Potassium bitartrate concentration and temperature. will often form on corks of older wines.
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Potassium Bitartrate Polyphenols
It is made by a ionic bond between an tartaric Grapes and wine contain a acid anion (negative) and a potassium cation number of polyphenols. A (positive). phenol is a molecule that contains a hydroxyl (OH) group on a benzene ring. Phenol itself is not found in wine. Phenol
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Potassium Bitartrate Polyphenols
Polyphenols are chains of these molecules, It is very common for KHTa to become that are present in the skins and seeds of insoluble and precipitate (come out of grapes. They can also come from the wood solution) in juice or wine lowering the TA during barrel aging. and changing the pH slightly. Approximate amounts Do not confuse: whites 100 to 300 PPM GAE (Gallic Acid Equivalents) TA (Titratable Acidity) with reds 1500 to 4000 PPM GAE Ta= (Tartrate ion).
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Wine Chemistry 9 2/25/2014
Polyphenols Anthocyanin Structures R R Responsible for color and sensory OH OH + characteristics (astringency and bitterness) H+ HO O O O R R that distinguishes reds from whites. Also a O-Gluc O-Gluc source of browning compounds. OH OH Quinoidal base (Blue) Flavylium cation (Red) R R H O + Very complex compounds that are OH 2 H OH OH OH O responsible for much of the body & color of HO HO O R R a wine. O-Gluc O-Gluc OH OH They can have positive affects on health. Chalcone Carbonyl pseudo-base
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Anthocyanins SO2: Bleaching of Anthocyanins R Polyphenolic red and blue pigments widely OH + HO distributed in plants. Found in the skins of O R
red grapes; white grapes do not have O-Gluc SO2 anthocyanins. OH Flavene Sulfonate R Flavylium cation (Red) Different anthocyanins have the same basic OH structure with variations. HO O R
Anthocyanin reactions with acids and sulfur O-Gluc H SO H dioxide affect color. OH 3
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Tannins Anthocyanins Tannins are a class of polyphenolic molecules R found in grapes that are similar to anthocyanins. OH They contribute to a wines astringency and + bitterness but are colorless. HO O R’ The get their name from leather tanning where
Delphinidin: R=OH; R’=OH plant tannins are used to cure animal skins. Cyanidin: R=OH; R’=H O-Gluc Peonidin: R=OCH ; R’=H Link to tannin article on class website. OH 3 Malvidin: R=OCH3; R’=OCH3
Petunidin: R=OCH3; R’=OH Pelargonidin: R=H; R’=H 57 60
Wine Chemistry 10 2/25/2014
Tannins Tannins are characterized by their ability to combine with proteins and polysaccharides. Example of These tannins can also polymerize with how tannins themselves, anthocyanins and other tannins and polymerize, a then settle out over time making older wines trimer of softer (less astringent). catechin They come from the skins, seeds, and stems of grapes. Oak tannins will also come from wood during barrel aging.
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Tannins Tannins There are three major types of tannins in wine: Tannins provide bitterness (flavor), Condensed, These tannins can polymerize astringency (sensation) to wine (as well as (form chains). Catechins are an example they coffee & tea). are found in grape skins, seeds, and stems. They help to protect the wine from oxygen Hydrolysable, ellagitannins are an example, and greatly influence how a wine will age. their primary source is wood (barrels). As tannins polymerize and grow larger they Complex, these are large chains of tannin will eventually precipitate out of the wine molecules that have formed polymers. making the wine softer and less tannic.
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Tannins Nitrogenous substances The structure of a monomer of catechin Important because amino acids (AAs) are made from nitrogen; AAs are the building blocks of proteins which all life is made up from. Ammonia 25 to 300 PPM in juice; rapidly assimilated by yeasts leave about 0 to 50 PPM in wine. Amino acids and proteins Contain about 90% of the nitrogen in grape juice.
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Wine Chemistry 11 2/25/2014
Nitrogenous substances
Amino acids & proteins are important because; Nutritional requirement by microbes Associated with formation of higher alcohols that affect sensory properties. Protein instability If nitrogen levels are too low, fermentation
can stick or produce H2S.
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Other must constituents Enzymes, are proteins that are catalysts, polyphenol oxidase is the most important. Vitamins, important as growth factors. Inorganics, potassium, calcium, copper, iron, magnesium. Pectins, colloidal substances such as polysaccharides. Volatile constituents, such as esters and pyrazines, very important but least understood.
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Composition of Wine vs. Juice Alcohols
Differences in composition are a result of Ethanol CH3CH2OH Ethanol has many microbial action (fermentation) on must or important sensory effects aroma, body, juice. viscosity, and taste. Main effect is due to We will now deal with the composition of alcohol acting as a solvent. wine. Also can have both positive & negative heath There are literally hundreds of compounds effects, as well as psychogenic effects. that exist in wine that contribute to its taste. Each wine has its unique combination that gives its signature taste.
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Wine Chemistry 12 2/25/2014
Alcohols Acetaldehyde - CH3CHO
Glycerol CH2OH-CHOH-CH2OH third Product of fermentation also a byproduct of most prevalent compound in most wines, aerobic spoilage organisms, results from and averages 0.6 to 0.8%. Has a big effect on indicates exposure to oxygen. Has a nutty- body or viscosity of a wine. sherry-like smell, 25 to 50 PPM.
Isoamyl alcohol (CH3)2CHCH2CH2OH A fusel oil that has a hot or heady smell mostly important in brandies.
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Alcohols Diacetyl Methanol, CH OH extremely small 3 Produced by ML bacteria amounts present, it is a poison! 6 to 10 ml can ML and has an intense cause blindness. Yeast do not produce nearly buttery aroma . enough to be a danger. There have been cases of methanol poisoning in wine but they were the result of adulteration by adding methanol to the wine.
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Acids from Fermentation Gasses
Lactic acid Small amounts formed by yeast, CO2 Leftover from fermentation it much more converted from malic acid by ML contributes to taste,. Young wines will have bacteria 3 - 5 g/L from 500 to 1500 PPM (parts per million). Contributes to the fresh flavor of young wines. Acetic acid CH3COOH Vinegar, small amounts formed by yeast much more formed O2 Contributes to aging and spoilage. Try to by spoilage bacteria, Acetobacter & Lactobacillus. keep it under 1 PPM for whites and less than 2 About 0.3 to 0.6 g/L PPM for reds. Too much is a sign of Succinic acid byproduct of alcoholic ferm NEGLECT! 0.5 - 2.0 g/L. 75 78
Wine Chemistry 13 2/25/2014
Urethane (ethyl carbamate) Some of the aroma compounds found in wine Norisoprenoids Carotenoid derived aromatic Carcinogen (also found in yogurt, bread) compounds including zingerone (spice notes), present in the ppt range, product of raspberry ketone, damascenone (rose oil) and fermentation increased dramatically when urea is added for nitrogen source. vanillin. UREA URETHANE Thiols, sulfur containing compounds that contribute to much of the varietal aromas of Cabernet Sauvignon, Sauvignon Blanc, Merlot, & Gewürztraminer. They include mercaptans (garlic and onion).
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Other Flavor Constituents Some of the aroma compounds found in wine There are many more volatile compounds that are created or modified by Esters, formed during fermentation and aging, microorganisms that are present in wine at aromas have wide range from fresh and fruity to very low levels. nail polish. These compounds are some of the most important and least monitored flavor components in wine.
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Some of the aroma compounds found in wine Tonight we have gone over the natural Methoxypyrazine, grassy, herbaceous aroma compounds commonly found in wine. compound associated with Cabernet Sauvignon Next week we will go over compounds that can and Sauvignon Blanc. be added to wine to affect its stability and flavor. Monoterpenes, responsible for the floral Sulfur Dioxide and Wine Additions lecture aromatics of Gewürztraminer, Muscat and next week after we review the test. Riesling. Includes geraniol, linalool and nerol.
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Wine Chemistry 14