Weekend Wine Word – Acidity

The quality of wine that gives it its crispiness and vitality. A proper balance of acidity must be struck with the other elements of a wine, or else the wine may be said to be too sharp – having disproportionately high levels of acidity – or too flat – having disproportionately low levels of acidity. The three main acids found in wine are tartaric acid, malic acid and lactic acid. The first two come from the grapes and the third from Malolactic fermentation which often occurs in the winemaking process.

tataric acid structure

Tartaric acid may be most immediately recognizable to wine drinkers as the source of "wine diamonds," the small potassium bitartrate crystals that sometimes form spontaneously on the cork. These "tartrates" are harmless, despite sometimes being mistaken for broken glass, and are prevented in many wines through cold stabilization. The tartrates that remain on the inside of aging barrels were at one time a major industrial source of potassium bitartrate.

However, tartaric acid plays an important role chemically, lowering the pH of fermenting "must" to a level where many undesirable spoilage bacteria cannot live, and acting as a preservative after fermentation. In the mouth, tartaric acid provides some of the tartness in the wine, although citric and malic acids also play a role.

malic acid structure

Malic acid is present in grapes. It confers a tart taste to wine, although the amount decreases with increasing fruit ripeness. The process of malolactic fermentation converts malic acid to much milder lactic acid.

Malolactic fermentation tends to create a rounder, fuller mouthfeel. It has been said that malic acid tastes of green apples – indeed, malic comes from the Latin word for apple, mālum, and is present in apple juice – and this can be tasted in the wine.

lactic acid structure

By contrast, lactic acid is richer, even unctuous, and more buttery tasting – corresponding to its presence in milk, as reflected in the word lactic being derived from the Latin word for milk, lac, and it is present in sour milk.

Information found on Wikipedia.