Acids in Wine - Other Acids

Other Acids

Acetic acid is a two-carbon organic acid produced in wine during or after the fermentation period. It is the most volatile of the primary acids associated with wine and is responsible for the sour taste of vinegar. During fermentation, activity by yeast cells naturally produces a small amount of acetic acid. If the wine is exposed to oxygen, Acetobacter bacteria will convert the ethanol into acetic acid. This process is known as the “acetification” of wine and is the primary process behind wine degradation into vinegar. An excessive amount of acetic acid is also considered a wine fault. A taster's sensitivity to acetic acid will vary, but most people can detect excessive amounts at around 600 mg/l.

Ascorbic acid, also known as vitamin C, is found in young wine grapes prior to veraison, but is rapidly lost throughout the ripening process. In winemaking, it is used with sulfur dioxide as an antioxidant, often added during the bottling process for white wines. In the European Union, use of ascorbic acid as an additive is limited to 150 mg/l.

Butyric acid is a bacteria-induced wine fault that can cause a wine to smell of spoiled Camembert or rancid butter.

Sorbic acid is a winemaking additive used often in sweet wines as a preservative against fungi, bacteria and yeast growth. Unlike sulfur dioxide, it does not hinder the growth of the lactic acid bacteria. In the European Union, the amount of sorbic acid that can be added is limited — no more than 200 mg/l. Most humans have a detection threshold of 135 mg/l, with some having a sensitivity to detect its presence at 50 mg/l. Sorbic acid can produce off flavors and aromas which can be described as “rancid”. When lactic acid bacteria metabolize sorbates in the wine, it creates a wine fault that is most recognizable by an aroma of crushed Pelargonium geranium leaves.

Succinic acid is most commonly found in wine, but can also be present in trace amounts in ripened grapes. While concentration varies among grape varieties, it is usually found in higher levels with red wine grapes. The acid is created as a byproduct of the metabolization of nitrogen by yeast cells during fermentation. The combination of succinic acid with one molecule of ethanol will create the ester mono-ethyl succinate responsible for a mild, fruit aroma in wines.