The two main and most important acids in wine are malic acid and tartaric acid, both of which exist naturally in grapes. Tartaric acid is the most predominant acid in warmer grape-growing regions. Unlike malic acid, the level of tartaric acid doesn't decrease as the grape ripens. In certain wine-growing areas where the level of grape acidity is typically low, tartaric acid can be added to wine to improve its acid balance.