Acidity, in cooking, is the sour or tart taste in food caused by organic acids such as citric, acetic, and malic acid, which occur naturally in many fruits, vegetables, and other ingredients.
Acidic ingredients such as lemon juice, vinegar, wine, and certain fruits and vegetables are used to cut through rich, fatty, or sweet elements and bring a dish into balance, particularly in sauces, marinades, dressings, and cuisines such as Mediterranean, Southeast Asian, and Latin American cooking.
Acidity also changes a food's texture and appearance: it helps tenderize tough cuts of meat, and, unlike heat, it slows enzymatic browning, which is why a splash of lemon juice keeps cut apples or avocado looking fresh. The same low pH that does this also inhibits bacterial growth, which is why acidity is central to preserving fermented foods like pickles, sauerkraut, and kimchi.
Acidity is a fundamental tool for balancing flavor, texture, and shelf life across the kitchen, and skilled cooks adjust it by taste rather than by a fixed rule.