Acids in wine

During the course of winemaking and in the finished wines, acetic, butyric, lactic, and succinic acids can play significant roles.

In most plants, this organic acid is rare, but it is found in significant concentrations in grape vines.

During fermentation, these tartrates bind with the lees, pulp debris and precipitated tannins and pigments.

The crystallization of these tartrates can happen at unpredictable times, and in a wine bottle may appear like broken glass, though they are in fact harmless.

It is found in nearly every fruit and berry plant, but is most often associated with green (unripe) apples, the flavor it most readily projects in wine.

The levels of malic acid in grape berries are at their peak just before veraison, when they can be found in concentrations as high as 20 g/L.

As the vine progresses through the ripening stage, malic acid is metabolized in the process of respiration, and by harvest, its concentration could be as low as 1 to 9 g/L.

It is produced during winemaking by lactic acid bacteria (LAB), which includes three genera: Oenococcus, Pediococcus and Lactobacillus.

This process can be beneficial for some wines, adding complexity and softening the harshness of malic acidity, but it can generate off flavors and turbidity in others.

Winemakers wishing to control or prevent MLF can use sulfur dioxide to stun the bacteria.

[6] While very common in citrus fruits, such as limes, citric acid is found only in very minute quantities in wine grapes.

During fermentation, activity by yeast cells naturally produces a small amount of acetic acid.

A taster's sensitivity to acetic acid will vary, but most people can detect excessive amounts at around 600 mg/L.

[2] 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.

[9] Sorbic acid is a winemaking additive used often in sweet wines as a preservative against fungi, bacteria and yeast growth.

[10] Succinic acid is most commonly found in wine, but can also be present in trace amounts in ripened grapes.

Grapes from cooler climate wine regions generally have higher levels of acidity due to the slower ripening process.

The level of acidity still present in the grape is an important consideration for winemakers in deciding when to begin harvest.

It adds a sharpness to the flavors and is detected most readily by a prickling sensation on the sides of the tongue and a mouth-watering aftertaste.