Glossary
Acidity
The sharp, mouthwatering quality in wine, mostly from tartaric and malic acid in the grape. It is what makes a wine taste fresh rather than heavy, and it is the single most important factor in whether a wine works with food.
In more detail
Acidity is largely determined in the vineyard: cooler climates and earlier picking retain more of it, heat and ripeness reduce it.
It is also what preserves wine over decades. Almost every long-lived wine is high in acid.