Reference

Winemaking Glossary

150+ winemaking terms explained in plain English.

A

ABV (Alcohol By Volume): The percentage of alcohol in a finished wine, calculated by measuring the difference between original and final gravity readings.
Acetaldehyde: A chemical compound produced during fermentation that can cause oxidized, sherry-like off-flavors if present in excess. Small amounts are normal.
Acetic Acid: The primary acid in vinegar. Produced by acetobacter bacteria in the presence of oxygen. Levels above 0.8 g/L are considered a fault.
Acid Blend: A mixture of tartaric, malic, and citric acids used to adjust the acidity (TA) of a must or wine.
Acidity (TA): Titratable acidity — the total measurable acid in wine, usually expressed in g/L. Ideal range for most wines is 5.5–8.0 g/L.
Aging: The process of maturing wine after fermentation, either in bulk (carboy/barrel) or in bottle, to develop complexity and smooth tannins.
Airlock: A device fitted to the top of a fermenter that allows CO₂ to escape while preventing oxygen and bacteria from entering.
Amelioration: The addition of water and/or sugar to a must to adjust acidity or sugar levels. Common in fruit winemaking.
Autolysis: The breakdown of dead yeast cells (lees) that releases compounds adding body and complexity. Key in sparkling wine and sur lie aging.

B

Barrel Aging: Maturing wine in oak barrels, which imparts flavors like vanilla, toast, and spice while allowing controlled micro-oxygenation.
Bâtonnage: Stirring the lees in a barrel or carboy to enhance body and mouthfeel. French for 'stirring with a stick.'
Bentonite: A clay fining agent that attracts and settles proteins, helping clarify white wines. Used at 1–2 g/L typically.
Brix: A scale measuring sugar content in grape juice. Each degree Brix roughly equals 1% sugar by weight. Multiply by 0.55 to estimate potential ABV.
Bung: A stopper (rubber or silicone) used to seal a carboy or barrel, often drilled to accept an airlock.

C

Campden Tablets: Tablets of potassium or sodium metabisulfite used to sanitize must and wine. One tablet per gallon provides approximately 30 ppm SO₂.
Cap: The layer of grape skins, seeds, and pulp that floats to the surface during red wine fermentation. Must be punched down or pumped over regularly.
Carbonic Maceration: A fermentation technique where whole grape clusters are placed in a sealed container filled with CO₂. Produces fruity, low-tannin wines (Beaujolais style).
Carboy: A large glass or plastic vessel (typically 3–6.5 gallons) used as a secondary fermenter for aging wine.
Chaptalization: Adding sugar to grape must before fermentation to increase potential alcohol. Legal in some regions, prohibited in others.
Cold Stabilization: Chilling wine to near-freezing to precipitate tartrate crystals before bottling, preventing harmless but unsightly 'wine diamonds.'
Cold Soak: Holding crushed grapes at low temperature (45–55°F) before fermentation to extract color and flavor without tannin.

D

DAP (Diammonium Phosphate): A nitrogen-rich yeast nutrient added during fermentation to prevent stuck fermentation and hydrogen sulfide production.
Degassing: Removing dissolved CO₂ from wine after fermentation, typically by stirring or using a vacuum pump.
Diacetyl: A buttery-flavored compound produced during malolactic fermentation. Desirable in some Chardonnays, considered a fault in most other wines.
Dry Wine: A wine with little to no residual sugar (below 4 g/L). The opposite of sweet wine. Most yeasts ferment to dryness naturally.

E

Enzyme (Pectic): Pectinase enzyme added to fruit must to break down cell walls, improving juice yield and clarity.
Extended Maceration: Leaving wine on the skins after fermentation is complete to extract additional tannin and color. Can range from days to months.

F

Fermentation: The metabolic process where yeast converts sugar into alcohol and CO₂. The fundamental chemical reaction in all winemaking.
Final Gravity (FG): The specific gravity reading of wine after fermentation is complete. Typical dry wines finish at 0.990–0.998.
Fining: The process of adding agents (bentonite, gelatin, egg whites, etc.) to attract suspended particles and clarify wine.
Free SO₂: The portion of added sulfite that is available to protect wine from oxidation and microbial spoilage. Measured in ppm (mg/L).
Fruit Wine: Wine made from fruits other than grapes — apples, berries, stone fruits, etc. Often requires sugar and acid adjustment.

G

Gravity: See Specific Gravity. The density of a liquid relative to water, used to measure sugar content and track fermentation progress.

H

Hydrometer: A glass instrument that floats in liquid to measure specific gravity. Essential for tracking sugar conversion during fermentation.
Hydrogen Sulfide (H₂S): A fault-indicating rotten-egg smell produced by stressed yeast, often due to nutrient deficiency. Preventable with proper yeast nutrition.

L

Lees: Sediment of dead yeast cells and grape particles that settles to the bottom of a fermenter. Fine lees can add complexity; gross lees should be racked off.

M

Maceration: The contact of grape skins, seeds, and stems with juice to extract color, tannin, and flavor compounds.
Malolactic Fermentation (MLF): A secondary bacterial process that converts sharp malic acid to softer lactic acid, reducing acidity and adding buttery complexity.
Must: Freshly crushed grape juice including skins, seeds, and stems — the raw material of wine before and during fermentation.

O

Oak: Wood used for barrels and alternatives (chips, spirals, staves) to impart flavor, tannin, and controlled oxygen exposure to aging wine.
Original Gravity (OG): The specific gravity of must before fermentation begins. Used with Final Gravity to calculate ABV.
Oxidation: Excessive exposure to oxygen that causes browning, flat flavors, and loss of fruitiness. Preventable with sulfite additions and minimal air contact.

P

pH: A measure of acidity/alkalinity on a logarithmic scale. Wine typically ranges from 3.0–3.8. Lower pH = more acidic, more stable, and more resistant to spoilage.
Potassium Metabisulfite: The most common source of sulfite (SO₂) in home winemaking. Used for sanitizing equipment and preserving wine.
Potassium Sorbate: A stabilizer that prevents renewed fermentation by inhibiting yeast reproduction. Used when back-sweetening wine before bottling.
Primary Fermentation: The initial, vigorous phase of fermentation lasting 5–14 days, during which most sugar is converted to alcohol.
Punch Down: Pushing the cap of skins back into the fermenting juice to maximize extraction and prevent spoilage. Done 2–3 times daily during red winemaking.

R

Racking: Carefully siphoning wine off its sediment (lees) into a clean vessel. Done 2–4 times during winemaking to clarify the wine.
Residual Sugar (RS): Sugar remaining in wine after fermentation. Measured in g/L. Dry wines have less than 4 g/L; sweet wines can have 45+ g/L.

S

Saignée: French for 'bleeding' — drawing off a portion of juice from a red wine tank early in maceration to make rosé and concentrate the remaining red wine.
Secondary Fermentation: The slower, quieter phase of fermentation after the initial burst, usually conducted in a sealed carboy with an airlock.
Specific Gravity (SG): The density of a liquid relative to water (1.000). Must typically starts at 1.070–1.100; dry wine finishes at 0.990–0.998.
Stuck Fermentation: A fermentation that stops before all sugar is consumed, often caused by temperature extremes, nutrient deficiency, or high alcohol toxicity.
Sulfite: Sulfur dioxide (SO₂) compounds added to wine as an antioxidant and antimicrobial preservative. Measured in ppm (parts per million).
Sur Lie: French for 'on the lees' — aging wine in contact with dead yeast cells to develop body, richness, and complexity.

T

Tannin: Phenolic compounds from grape skins, seeds, stems, and oak that contribute bitterness, astringency, structure, and aging potential to wine.
Tartaric Acid: The primary acid in grapes and wine. Responsible for crispness and freshness. The most important acid for acid adjustment.
Terroir: The complete natural environment in which a wine is produced — soil, climate, topography, and ecosystem. The 'taste of place.'
Topping Up: Adding wine to a carboy or barrel to fill the headspace, minimizing oxygen exposure during aging.

V

Volatile Acidity (VA): Acidity from volatile acids (mainly acetic acid) that can be detected as a vinegar-like smell. A fault when excessive.

Y

Yeast: Single-celled fungi (primarily Saccharomyces cerevisiae) that consume sugar and produce alcohol and CO₂ during fermentation.
Yeast Nutrient: Supplements (DAP, Fermaid-K, etc.) providing nitrogen and micronutrients to yeast for healthy, complete fermentation.