Wine and Alcoholic Fermentation (I)

Wine Fermentation Grape cultivation and wine making from

Zagros Mountains and Caucasus region of Asia from 6000 B.C.E.

Wine-like product with honey and fruit from China ~7000 B.C.E.

One of the oldest of all fermented products been commercialized, mass produced and studied

Wine Fermentation 75% made in the Mediterranean areas of

Europe France, Italy, Spain produce more than half of

the 27 billion liters produced from around the world

Knowledge of biochemistry and microbiology started from understanding wine fermentation Pasteur

Wine Fermentation Australia, South Africa, Chile >10% world

production, significant export US more than 2 billion liters/year, 90%

from California Impact of California wine industry ~$33

billion France, Italy, US, Germany, Spain top wine

consuming countries Luxembourg France and Italy drink >50

L /person.year; US~9 L/person annually

Wine fermentation “Value added” process A bottle of wine from 1847 France sold for

$71,675 in LA in 2004 Wine vs. beer fermentation

Alcoholic fermentation Different yeasts and substrates

99% wine from grapes, rest from juices of other fruits with enough sugar (make >12% ethanol by vol)

Distinct products Consume fresh vs. aged Quality dependent on the quality of raw materials

Viticulture and Grape Science Varies in grape species and cultivars

Vitis vinifera, V. labrusca Cabernet Sauvignon, Chardonnay, Gamay, Mission, etc. refer

to different varieties or cultivars of the Vitis vinifera

Cabernet Sauvignon Chardonnay Gamay Mission

Different in compositions (sugar contents, pigmentation, etc.) Different climates and soil preference Wine quality varies greatly

Climate factors have important effect on grape quality and maturity

Grape Composition Water 70-85% of the juice vol About 20% sugar

Simple sugars largest constituent of grapes or must Important for S. cerevisiae to produce ethanol Glucose (~50%), Fructose (~50%, increase in over-

ripened grapes), sucrose (<1%, in V. labrusca up to 10%)

Other sugars very low conc. Sugar content in final product

“dry”: 0.1%-0.2% “sweet” >10g/L “very sweet” as much as 100g/L-200g/L

Other Components Organic acids

Second plentiful non-water constituent in must Extremely important in wine quality

Provide low and well buffered pH (3.0-3.5) Antimicrobial activities Stabilizes anthocyanins (color, antioxidant, desirable

flavor) Volatile acids (acetic acid and others) very low Fixed acids (malic acid and tartaric acid ~5:1)

important to maintain the right acidity of wine and anti-spoilage, affected by environmental factors

Nitrogenous Compounds Total N range from 0.2g/L to 0.4g/L Generally adequate for rapid growth of

yeast Presence of biogenic amines (histamine

and tyramine) in wine (by wine bacteria) can cause adverse reactions

Ethyl carbamate potential carcinogen, conc. increased by heat treatment and high urea conc.

Sulfur Compounds Hydrogen sulfide (H2S) and other organic

derivatives (mercaptans) by grape yeasts impart offensive flavor

Sulfur dioxide (SO2) and derivatives

naturally produced by yeast Also added due to antimicrobial, antioxidant,

antibrowning properties

Phenols Tannins and Pigments Phenolic and polyphenolic compounds

naturally occurring in grapes, some be introduced later

Contribute to color, flavor, aroma, mouth feel to the wine

Wine Making Harvesting and preparing grapes for wine making

Harvest at right level of maturity Manually picked grapes for premium wine Manual picking also for sweet wines from noble rot grapes,

or certain wines with regulated grape harvesting methods Crushing and Maceration

Remove extraneous material Crush Maceration: crushed grape material allowed to sit to extract

more compounds Long and high temp for darker-colored red wine Very short and low temp for white wine (some remove seed

sand skin right away)