Tartaric acid is the principal and most stable organic acid in grapes and wine. It contributes freshness, structure and microbial stability, and it plays an important role in wine chemistry. Along with malic acid, it is one of the main acids present in grape juice, although its concentration and effect vary with variety, climate, ripeness and winemaking.
Tartaric acid contributes to the wine’s total acidity and influences pH. It helps create freshness and balance, particularly in wines with ripe fruit or residual sugar. Winemakers may measure titratable acidity and pH to understand how the wine will taste and how stable it may be during production and storage.
Tartaric acid can combine with potassium in wine to form potassium bitartrate crystals. These crystals may precipitate during cold storage and appear on the cork or at the bottom of the bottle. They are harmless and are sometimes called “wine diamonds.” Cold stabilisation is used by some wineries to reduce the likelihood of crystals forming after bottling.
Where permitted, tartaric acid may be added to must or wine to adjust acidity. Winemakers generally use laboratory analysis and bench trials to determine the appropriate addition. Excessive acidification can make a wine taste sharp or unbalanced, so the adjustment must be carefully controlled and comply with regional rules.
Example: a winery may add a measured amount of tartaric acid to a low-acid must in a warm vintage to improve freshness and balance.
Tartaric acid is relatively stable and can form tartrate crystals. Malic acid has a sharper, green-apple character and can be converted into softer lactic acid during malolactic fermentation. Lactic acid contributes a rounder acidity.
Chef’s note: tartaric acid is also used in food production, but wine acidity cannot be judged from one acid alone. pH, total acidity and the wine’s other components all influence the final taste.
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