ENOLOGY

Overview

History

Key Terms

  • autolysis: disintegration of yeast cell walls, which adds amino acids, enzymes, and lipids into the wine; produces secondary aromas and flavors

  • lees:

  • sur lie: "on the lees"; practice of allowing wine to rest on dead yeast cells to add secondary aromas and flavors

Wine Components

Acid

  • Typically 0.5% to 0.75% of volume

  • Six main types:

    1. Acetic acid: not found in grapes but is a product of alcoholic fermentation from the bacteria acetobacter; a volatile component that adds to aromas at low amounts; produces a wine fault, volatile acidity, at high amounts

    2. Citric acid: a very minor (often undetectable) component in grapes; sometimes added to wine to increase its total acidity

    3. Lactic acid: not found in grapes but is a product of malolactic conversion from the bacterial family Oenococcus oeni; softer than malic acid, MLF produces a creamy texture and buttery aroma in some wines

    4. Malic acid: a major component in grapes; sharp taste of green apples; levels drop as grapes ripen; more commonly found in ripe grapes in cooler climates than warmer ones; transformed into lactic acid during malolactic conversion

    5. Succinic acid: a minor component in grapes and a product of alcoholic fermentation; has a sharp, slightly bitter, slightly salty flavor

    6. Tartaric acid: the most prevalent acid in grapes; strongest in terms of pH; crystalizes at low temperatures, producing tartrates or "wine crystals," and does not redissolve into wine; can be avoided with cold stabilization techniques

pH

  • Represents the chemical strength of the acids present in wine

  • Typically ranges between 2.9 and 3.9 on the pH scale

  • Considered a reliable measure of a wine's stability and assessed for potential addition of sulfites

Total Acidity

  • Also known as titratable acidity

  • Represents the total volume of acids present in wine

  • A high TA may not equate to high acidity in flavor if the acids have a higher pH (like lactic, which is softer than malic)


Alcohol

  • Typically 10-15% of volume

  • Contributes body and weight to wine

  • Four main types:

  1. Ethyl alcohol: also known as ethanol; primary result of alcoholic fermentation and main alcohol in wine; a volatile compound that allows aromas to rise from wine

  2. Glycerol: third most abundant component in wine, usually around 1%; a product of alcoholic fermentation; more prevalent in botrytized wines; adds sucrosity, if not necessarily body or viscosity

  3. Methyl alcohol: also known as methanol

  4. Fusel alcohols: also known as fusel oils or higher alcohols


Phenolic Compounds

  • Also known as phenolics, polyphenolics, or polyphenols

  • Various molecules that, although limited in volume, have a major impact on wine

  • Concentrated primarily in grape skins, seeds, and stems

  • Over time, some phenolic compounds can polymerize, chaining together to such a degree that they precipitate from wine as sediment; after extreme aging, they can break down again

  • Five main types:

    1. Anthocyanins: red, purple, and blue pigments that give red wines their color; affected by a wine's acidity; more acidic wines appear redder in hue, whereas less acidic wines appear bluer

    2. Flavonols: also known as flavones; yellow pigments that give white wines their color; increase in volume as grapes are exposed to sunlight; sunnier climates produce more golden wines than cooler or cloudier climates

    3. Resveratrol: a component that, although considered beneficial to health, has not been proven in many studies to have much salutary effect

    4. Tannins: general group of astringent, bitter compounds; also found in oak barrels; add structure and aging ability to wine, given their ability to slow oxidation

    5. Vanillin: aromatic compound derived from oak; same compound as found in vanilla


Sugar

  • Grapes typically contain between 15 and 28% sugar at harvest

  • Two main types, both monosaccharides or simple sugars:

  1. Fructose

  2. Glucose

  • Residual sugars are those remaining in wine after fermentation, whether on the part of a winemaker's intervention or natural causes

  • Adds weight, viscosity, body, and texture to wines


Water

  • Typically 80-90% of volume

  • On rare occasions, winemakers add water to dilute concentrated components


Other Components

  • Four main types:

  1. Aldehydes: oxidized alcohols formed when wine is exposed to air; most common form is acetaldehyde, or oxidized ethyl alcohol; sometimes a desirable and intentional product, as for Sherry or Madeira; can occur when wines are open too long or exposed to heat

  2. Esters: combination of acid and alcohol molecules; largest group of odor-producing compounds in wine; most common form is ethyl acetate, a combination of ethyl alcohol and acetic acid, which produces fruity and floral aromas in low concentrations and faulty aromas of nail polish remover at high amounts

  3. Gases: most common dissolved gas in wine is oxygen; sulfur often added to wine to absorb oxygen; carbon dioxide also common, both in still wines (which provides pétillance) and as the main textural component of sparkling wines

  4. Sulfites: group of chemicals composed of sulfur; natural product of fermentation; often added as preservative and antibacterial agent

Main Winemaking Processes

Red Winemaking

White Winemaking

Rosé Winemaking

Sweet Winemaking

Winemaking Options

Adjustments

Chaptalization


Maturation

Wine Faults