McGee's treatment of starch gelatinisation explains why sauces thicken, why bread has structure, why custards set, and why pasta is al dente — all through the same underlying chemistry. Understanding starch as a structural and thickening material rather than merely a carbohydrate transforms approach to every sauce, baked good, and cooked grain.
A framework for starch gelatinisation — the process by which starch granules absorb water, swell, and rupture when heated, releasing amylose and amylopectin molecules that form a network trapping water and producing viscosity.
- Gelatinisation begins at different temperatures for different starches: potato starch at 58–65°C, cornstarch at 62–72°C, wheat starch at 52–63°C, arrowroot at 58–68°C, tapioca at 52–64°C [VERIFY ranges] - The gelatinisation process is not instantaneous — the sauce thickens progressively as more granules swell and rupture. Premature removal from heat leaves ungelled starch that produces graininess - Retrogradation: cooked starch cools and the amylose molecules re-associate, expelling water (syneresis) and becoming firmer. Day-old bread is stale because of retrogradation. Day-old polenta is firm because of retrogradation. This is reversible with heat — day-old bread re-softens briefly when warmed. - Different starches produce different textures: cornstarch produces a glossy, clear gel; flour produces an opaque, matte gel; arrowroot produces a clear gel that does not cloud when cooled; potato starch produces a short, not stringy, gel - Acid inhibits starch thickening — highly acidic preparations (fruit sauces, some Chinese sauces) require more starch to achieve the same thickening as neutral preparations [VERIFY]
JOSH NILAND: THE WHOLE FISH COOKBOOK + HAROLD McGEE: ON FOOD AND COOKING