Glossary of Winemaking Terms

The whole point here is to keep things simple and easy to understand, yet winemaking jargon inevitably creeps in. Hopefully this glossary will help.

A | B | C | D | F | I |L | M | O | P | R | S | T | Y

Acid balanceSeveral components of wine (acid, residual sugar, amount of fruit flavour, alcohol, astringency) contribute to its texture and mouthfeel. Wine quality is improved if these components are in good balance, so that the wine tastes harmonious, rather than, for instance, tasting too sweet, dry, or sour. Acid is one of the components that can be relatively easily adjusted, and affects the perceived levels of other components such as sweetness and astringency. Winemakers make trial acid additions on a small scale, taste them, then choose the best level to add to the tank.
AntioxidantSubstance that prevents oxidation, and hence protects wine quality (particularly in whites), as oxidation destroys fresh and fruity aromas.
AstringentThe skins and seeds of grapes contain tannins which cause a dry, rough feeling in the mouth, and this rough feeling is termed astringency. This accounts for the main difference in taste between red and white wines, as whites are fermented without contact with the skins and seeds and therefore contain very little tannin. Tannins also cause the astringency of black tea and unripe fruit.
Bitartrate crystallisationTartaric acid in grape juice is partly neutralised by potassium released from the grape skins after the grapes are crushed. This forms potassium bitartrate (also known as potassium hydrogen tartrate or cream of tartar) which is much less soluble and therefore needs to crystallise out. However, this crystallisation is slow, so in white winemaking, where the maturation of the wine before bottling is brief, measures are taken to "cold stabilise" the wine before bottling. Tartrate crystals forming in the bottle ("wine diamonds") are harmless but unsightly.
CatalystA catalyst increases the rate of chemical reactions. In winemaking, enzymes are natural catalysts that increase the rate of reactions such as the breakdown of pectin. Metals such as copper are strong catalysts of oxidation, hence winemakers use only stainless steel and avoid contamination with metals such as iron or copper.
ClosureThe object sealing the bottle, traditionally a cork, but now normally the screwcap.
Cold-stabilisingSee Bitartrate crystallisation.
DeacidificationUnripe grapes, like other fruits, contain little sugar and much acid. As they ripen, sugar accumulates at the expense of acid. Ideally the grapes are picked when the two are in a balance that will taste good in the finished wine. Often, in warm climates, acid addition is required to achieve this balance. In cold climates, deacidification may be required, and this normally refers to the partial neutralisation of the wine acids with a base such as bicarbonate. Malolactic fermentation is an alternative means of deacidification, but better suited to some wine styles than others as it also modifies wine flavours.
DisgorgingThe final step in the traditional method of making sparkling wine. Yeast sediment is removed from the bottle, which is then topped up with wine and a sweetening liqueur.
FermentationA process carried out by microbes. In wine, the alcoholic or primary fermentation is carried out by yeast and involves the conversion of grape sugar into alcohol and carbon dioxide. The secondary or malolactic fermentation is mainly done in red wines and involves the conversion by bacteria of malic acid into lactic acid.
FiningThe process of removing something undesirable in wine by binding it to something else. Generally, when the two are bound they form particles large enough to settle to the bottom of the tank and can then be separated from the clear wine. Common examples are the binding of tannins with protein-rich agents such as egg white or milk, binding of proteins with bentonite, or binding of sulphides with copper.
Inert gasA gas that does not react with the wine, unlike the oxygen in air which causes oxidation. When oxidation is to be avoided, an inert gas such as nitrogen, carbon dioxide or argon may be used to form a protective layer between the wine and the air.
LeesAnything that forms a sediment at the bottom of the tank or barrel is referred to as lees. Typically, lees consists of grape solids or yeast.
Malolactic fermentationThe conversion by specific bacteria of malic acid in wine to lactic acid. Lactic acid is less acidic, so this softens the wine, but also makes it more stable as the malic acid food source is exhausted, so that the bacteria cannot subsequently grow in bottle.
MouthfeelSimply how the wine feels in the mouth, such as whether it is full-bodied or light, rich or thin, soft or astringent.
MustThe mixture of skins, seeds and juice achieved by crushing the grapes. For red wines, the must is fermented directly, while for white wine, the must is first pressed so that the juice can be fermented without the skins.
OxidationChemical reactions that take place particularly when wine is exposed to air and hence oxygen. Some oxidation reactions under certain conditions are positive, such as in the maturation of red wines in barrel, but many are negative, such as when the fresh fruity aromas of white wines are oxidised to duller, less fresh aromas.
PectinasesA type of enzyme naturally present in grapes which is released at crushing and degrades pectin into smaller fragments. This breakdown helps the juice or wine to clarify naturally.
pHThe 'power of hydrogen', meaning the concentration of hydrogen ions in a solution such as juice or wine. Hydrogen ions are released by acids, so pH is a measure of the acidity of the sample.
PhenolicsA complex group of compounds present in grapes and more or less extracted into the wine depending on winemaking technique. Phenolics include tannins and contribute the drying astringency typical of red wine, but can also affect the mouthfeel of white wines. Phenolics are negative in some white wine styles as they give coarseness to the palate.
RackingThe process of drawing off (usually by pumping) the clear juice or wine from the upper portion of a tank, leaving a layer of lees (solids) at the bottom.
Reductive character/reductionUnder some circumstances that usually include an absence of contact with air, sulphur compounds in wine may become reduced, and these reduced compounds are smelly. Rotten egg gas (hydrogen sulphide) is a common example. Care must be taken to avoid or deal with these situations. Reduction is the opposite of oxidation, so controlled exposure to air is one way of solving the problem.
Residual sugarGrape juice at the beginning of fermentation is very sweet. Healthy yeast in a normal fermentation can consume all the grape sugar, but if the fermentation stops for some reason or is stopped by the winemaker, then residual sugar will remain in the wine. Reserved grape juice or grape juice concentrate may also be added back to a wine that has finished fermentation (i.e. is 'dry') and in this case it is also often referred to as having residual sugar.
StabiliseThe winemaker aims to stabilise wine before bottling, so that various undesirable things do not happen in bottle. White wines in particular are 'cold stabilised' to prevent bitartrate crystallisation in bottle. Wine is 'heat stabilised' in order to prevent protein haze developing in bottle. Red wines are automatically heat stable through the action of tannin, but white wines have to be stabilised by the use of bentonite. All wines need to be microbially stable in bottle, meaning that no yeast or bacteria will grow in them after bottling.
StructureA tasting term referring to textural or physical characteristics of the wine, influenced by components such as acid, sweetness, alcohol and particularly tannin.
SulphidesReduced forms of sulphur, associated with generally unpleasant aromas. See also reductive character.
SulphitesForm which sulphur dioxide takes in solution, so a term used interchangeably with sulphur dioxide.
TanninGroup of compounds derived from grapes which give an astringent or drying character to the mouthfeel of the wine. Tannins also enter the wine by contact with oak (such as barrels).
TirageStep in the traditional method of making sparkling wine where yeast and sugar are added to the base wine at bottling, so that a fermentation takes place in bottle where the carbon dioxide cannot escape and therefore makes the wine fizzy.
YANYeast Assimilable Nitrogen, a measure of the natural nitrogen-containing nutrients present in grape juice that the fermentation yeast can use.
Yeast autolysis After fermentation is complete, the yeast cells are left without any food and gradually die over a period of weeks. The dead yeast cells gradually break down, releasing cell components into the wine. Some of these add flavour and texture to the wine.