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Starch gelatinisation

The swelling and bursting of starch granules in hot water, which thickens sauces and cooks grains.

60โ€“95 ยฐC (140โ€“203 ยฐF)

What it is

Dry starch granules are hard and insoluble. In water above a certain temperature they absorb it, swell many times over, and eventually rupture and release long starch chains that tangle and thicken the liquid.

Why it works

Each starch has its own range โ€” cornflour around 62โ€“72 ยฐC, wheat a little higher, potato lower and more dramatic. Below it, nothing thickens; this is why a sauce thickened with flour must come to a simmer, and why a slurry stirred into a cool liquid does nothing until it heats.

When to use it

Roux and slurry sauces, custards, rice, pasta, potatoes, bread, gravies.

What goes wrong

Not heating far enough, leaving a raw, floury taste; boiling a cornflour sauce hard for a long time, which breaks the chains and thins it again; adding acid early, which also shortens them.

Meridian cooking encyclopedia โ€” Watchman Productions