Vegetables, Fruits and Starches
Pigments and plant structure
Chlorophyll (green) turns olive-brown with acid or long heat; cooking quickly, uncovered, in plenty of boiling water preserves colour, and an ice bath sets it. Carotenoids (orange/yellow) are fairly stable but oxidize. Anthocyanins (red/purple) turn blue-green in alkali and are preserved by acid-red cabbage cooked with vinegar or lemon stays red. Flavones (white/cream) yellow with alkali. Pectin, hemicellulose and cellulose are the fibres; acid firms pectin and slows softening, alkali softens it but makes vegetables mushy.
Enzymatic browning and fruit
Polyphenol oxidase browns cut apples, potatoes and avocado; control it with acid, salt, blanching or exclusion of oxygen. Fruits are graded by ripeness; ethylene gas from apples and bananas speeds ripening of neighbours in storage.
Starches
Gelatinization occurs when starch granules absorb water and swell with heat; retrogradation is the reverse-staling and syneresis, the weeping of a cooled starch gel. Sugar raises the gelatinization temperature and salt can too; acid hydrolysis thins a starch gel. Know waxy versus mealy potatoes, rice types (long grain, short grain, arborio, basmati), pasta (al dente, fresh versus dried), and legumes, which need a soft-water, acid-free cooking liquid to soften.
Rule of thumb: boil green vegetables uncovered in abundant salted water for 2–5 minutes, then shock in ice water to stop carryover and set chlorophyll.
Traps: adding acid early to legumes; salting pasta water too late; confusing gelatinization with retrogradation; thinking baking soda improves texture when it mainly destroys it.