Wine terminology

ABV

Alcohol by volume. The percentage of alcohol in the finished wine.

Acidity

The acids in wine that provide freshness, balance and structure. Fruit, flowers and vegetables vary naturally in acidity.

Airlock

A one-way valve fitted to a fermenting vessel. It lets carbon dioxide escape while helping keep air and contaminants out.

Campden tablet

A measured source of sulphite commonly used in winemaking to help control unwanted microorganisms and protect wine from oxidation.

Clearing

The stage when suspended particles settle or are removed so the wine becomes bright and clear.

Demijohn

A vessel, traditionally glass or PET, used for secondary fermentation, clearing and ageing. A UK gallon is about 4.5 litres.

Fermentation

The process in which yeast converts fermentable sugars into alcohol and carbon dioxide.

FG

Final Gravity. The specific gravity measured when fermentation has finished and the wine is stable.

Hydrometer

An instrument used to measure specific gravity. Comparing readings helps show whether fermentation is progressing and can help estimate alcohol.

Must

The unfermented mixture of prepared ingredients, water, sugar and other recipe ingredients before fermentation is complete.

OG

Original Gravity. The specific gravity measured before fermentation. Comparing OG with FG gives an estimate of alcohol production.

Pectic enzyme

An enzyme used to help break down pectin in fruit and some plant material, improving juice extraction and helping wines clear.

Primary fermentation

The vigorous first stage of fermentation, usually carried out in a larger vessel with room for activity and solids.

Racking

Transferring wine from one vessel to another, usually leaving sediment behind.

Secondary fermentation

The slower stage after the vigorous primary fermentation, normally carried out in a demijohn or similar vessel under an airlock.

Specific gravity

A measure of the density of the liquid compared with water. In winemaking it is commonly used to track sugar consumption during fermentation.

Tannin

Naturally occurring compounds that contribute structure, grip and sometimes bitterness. They are found in fruit skins, seeds, tea and some other ingredients.

Yeast nutrient

A nutrient blend supplied to help wine yeast ferment reliably, particularly where the main ingredients are low in yeast-available nutrients.

Wine yeast

A yeast strain selected for alcoholic fermentation. Different strains can vary in alcohol tolerance, temperature range and flavour contribution.