Acidity is a key component of wine

Wine’s acidity originates in grapes, but acid is also created during winemaking and aging. Wine contains two types of acids: fixed and volatile. Fixed acids, also called stable acids, remain in a liquid when it’s boiled, while volatile acids readily evaporate.

Wine’s fixed acids are tartaric, malic, lactic, citric, and succinic. These acids give a wine structure, texture, and zing. Wine’s volatile acids are acetic, butyric, formic, isobutyric, propionic, hexanoic, sorbic, and sulfurous. These volatile acids are present in smaller quantities than the fixed acids.

We sense wine’s fixed acids texturally, and its volatile acids aromatically.

Tartaric, malic, and acetic acids play significant roles in wine

The most important fixed acids in wine are tartaric and malic. Grapes have an uncommon abundance of tartaric acid, which gives the wine tanginess and structure. Tartaric acid precipitates out of wine over time, forming tartrate crystals. Malic acid is abundant in grapes and survives primary yeast fermentation, but may undergo a change that weakens its potency during malolactic conversion, which transforms it into lactic acid.

The most important volatile acid in wine is acetic acid. Acetic acid is a byproduct of both yeast fermentation and oxidation. This is the same acid in vinegar, but there’s far less of it in wine. Below the perception threshold of about 1.2 g/L, acetic acid puts a shiny polish on the wine’s aromatic profile.

Aged wines have more acetic acid, and at end of a wine’s life the vinegar aroma and flavor are pronounced. When acetic is present at high concentrations, and especially in combination with another volatile compound, ethyl acetate, the wine is regarded as having elevated volatile acidity.

Talking about acidity in wine

Wine writers generally assess the combined impact of all of these acids, describing it broadly as low, medium, or high, although commentary may focus on the presence of tart, green-apple flavored malic versus smoother, softer lactic. Wines at the extreme ends of the acidity spectrum—too low, too high—are often described as unbalanced.

• Wines with low or insufficient acidity may be described as soft or flabby.

• Wines with medium acidity might be called fresh, crisp, bright, or lively. Those with a bit more may be described as racy, nervy, linear, zesty, or crunchy.

• Wines with excess or high acidity may be described as bracing, tart, or sour.

• Wines with elevated volatile acidity may be described as lifted or high-toned (if it’s pleasant), or simply volatile (if it’s not).

Read more on acidity in wine in these two features:

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