MALOLACTIC FERMENTATION

Acidity is a general term for the fresh, tart or sour taste produced by the natural organic acids in liquids. Acids are important in wine because, in moderation, they make a wine taste refreshing and reduce harmful bacteria to help keep it microbiologically safe. Wines owe their attractive qualities to a proper balance of the acidity with the sweetness and bitterness of other
components. Too much acidity can make wines sharp, tart or even physically uncomfortable to drink. Too little acidity results in wines that are flat and uninteresting (“flabby” is the wine term).
Malic acid is one of the principal organic acids found in grapes and wines and is the acid which gives a wine its tart appley characteristics. Malic acid is reduced as the grapes ripen on the vine. This process occurs more readily in warmer temperatures and is one reason for the lower total acid concentrations in grapes grown in warmer regions. But malic acid is not lost just during
grape ripening, it is also reduced as a result of malolactic fermentation (also known as MLF).
MLF is the conversion of the stronger malic acid naturally present in new wine into the much milder lactic acid which is also found in milk products. The conversion is accomplished by lactic bacteria which are naturally present in most established wineries. This process is unrelated to and almost never precedes the alcoholic fermentation and is sometimes called a secondary fermentation.
MLF is desirable in wines which have excessive acidity. It can also add flavor and complexity to wines as well as preventing malolactic fermentation in the bottle. Now most fine red wines, many sparkling wines and a small but increasing proportion of the world’s white wines undergo full or partial MLF. Of white grapes, Chardonnay is often a candidate for MLF, while most producers of Riesling and Chenin Blanc avoid the process.

Information was researched from The Oxford Companion to Wine edited by Jancis Robinson.