Chapter One: Wine Composition And Chemistry

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Major components of wine

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water, alcohol, acid, sugar, phenolic compounds; (bacteria, yeast, proteins, other compounds)

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Wine component: water

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80-90% water

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Wine component: alcohol

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10-15% alcohol; ethyl alcohol (ethanol), glycerol, methyl alcohol (methanol), fusel oils (fusel alcohols or higher alcohols)

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Wine component: acid

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0.5-0.75% acid; tartaric acid, malic acid, citric acid, lactic acid, acetic acid, succinic acid

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Tartaric acid

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most prevalent of the acids; strongest pH of the acids; forms "tartrates" (wine diamonds) @ low temperatures

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Tartrates

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wine diamonds formed from tartaric acid @ low temperatures; will not redissolve and will cause wine to be less acidic; mitigated through cold stabilization however not considered a defect

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Malic acid

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sharp-tasting "green apple" acid found in cool-climate and *under-ripe grapes; mitigated through maloactic fermentation

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Maloactic fermentation

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conversion of malic acid into lactic acid by lactic acid bacteria

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Citric acid

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not considered a "normal component" of grapes as is only measurable by specialized equipment (no sensory impact); occasionally added to increase acidity (citrus-fruit flavor however, unsuitable for quality wines)

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Lactic acid

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not found in grapes, created in wine by lactic acid bacteria (maloactic fermentation); leads to softer/smoother and creamier/butterier wines

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Acetic acid

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found in most vinegar; low-levels created during fermentation; volatile acid (readily evaporates and joins the aromas of wine); in high concentrations can make a wine undrinkable

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Acetobacter

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bacteria in wine that creates "acetic acid" (caused by a chemical reaction between ethanol and oxygen); in high concentrations can make a wine undrinkable

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Succinic acid

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minor component in grapes (by-product of fermentation); sharp, slightly bitter, salty flavor profile

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Total acidity (TA)

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volume of all the acids in a wine; includes several different acids (some of which are stronger than others)

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pH scale

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0 (acidic) - 7 (basic); represents the combined chemical strength of the acids present; wine = 2.9-3.9

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Wine component: sugar

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15-28% sugar @ harvest; equal amounts of glucose and fructose

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Glucose and fructose

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highly fermentable monosaccharides (simple sugars); converted into ethanol by yeast

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Wine component: phenolic compounds

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polyphenols; polyphenolics; phenolics; large category of various molecules (occurring in minute quantities primarily in the skin and seeds) present in many wines; can have a major impact on the sensory profile of the wine

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Anthocyanins

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phenolic compound; gives red wine its colour (along with the level of acidity)

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Flavonols

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phenolic compound; "flavones"; yellow pigments found in white grapes; increased in grapes with more exposure to sunlight

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Tannins

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phenolic compound; astringent, bitter compounds found in the skins, seeds and stems of grapes; also found in oak and oak barrels

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Vanillin

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phenolic compound; aromatic compound found in oak barrels (same compound found in vanilla beans)

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Resveratrol

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phenolic compound; MAY better protect against heart disease, dementia, Alzheimer's, stroke, osteoporosis, peptic ulcers; MAY treat type 2 diabetes (helping the body to overcome insulin resistance)

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Polymerize

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combination of molecules into longer molecule chains; occurs to phenolic compounds over time (particularly tannins and pigments); these chains drop out of solution as sediment when too heavy (aging process); sediment renders a wine lighter in color and less astringent

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Wine component: other compounds

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aldehydes, esters, dissolved gases, sulfites

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Aldehydes

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wine compound (other); oxidized alcohols that are formed when wine is exposed to air; encouraged by Sherry and Madeira; most common aldeyde: acetaldehyde

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Acetaldehyde

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most common aldehyde (wine compound); formed by the oxidation of ethanol; gives fino sherries their distinctive aroma

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Esters

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wine compound (other); molecules that result from the joining of an acid and an alcohol; represent the largest group of odiferous compounds found in wine; desirable in LOW concentrations

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Ethyl acetate

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most common ester (wine compound); the ester of acetic acid and ethanol; low concentration (fruity, flowery aroma); high concentration (nail polish remover, varnish, glue aroma)

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Dissolved gasses

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wine compound (other); oxygen (oxidation prevented through the addition of sulfur); carbon dioxide [C02] (bubbles in sparkling wine, natural by-product of fermentation)

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Sulfites

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wine compound (other); class of chemicals based on Sulfur [S]; added during winemaking AND natural by-product of fermentation; preservative to keep wine stable after fermentation; antioxidant; antibacterial agent

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"Contains Sulfites"

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>10 parts per million (ppm); required on labels in the US