Lesson 2. Acid and fat: contrast and richness

Acid (lemon juice, vinegar, tomatoes, tart berries) brings contrast and “freshness” to a dish's flavor. A fatty, heavy dish tastes lighter and brighter after a drop of acid. That's why lemon is served with fatty fish, pickled onions and vinegar with grilled kebabs, and a spoonful of sour cream or a drop of vinegar with a rich soup. Acid seems to “cut through” fat and keeps a dish from being cloying or getting tiresome. Acid also balances sweetness. Jam or a sauce that has only sugar in it quickly gets tiresome. Add a little citric acid or lemon juice, and the flavor comes alive while the sweetness stops being overbearing. The classic sweet-and-sour pairing (sauces for meat, Asian cooking) rests on exactly this balance. Fat plays a different role. First, many aroma and flavor compounds dissolve in fat, not in water, so fat carries flavor. That's why spices, onions, and garlic are fried in oil: the oil draws out their aroma and spreads it through the dish. Second, fat coats the tongue, gives a sense of richness, and smooths out harsh flavors. Cream or a pat of butter softens a dish that's too spicy or too sour. The principle: if a dish seems heavy or cloying, add acid. If it's flat, harsh, or too spicy, fat may help. Salt, acid, and fat are knobs you tune flavor with; the fourth, umami, comes in the next lesson.