cornstarch
Also known as: corn starch
A fine, powdery starch extracted from corn, used to thicken sauces, gravies, and fillings. It's almost always mixed with cold liquid into a smooth slurry before going into something hot -- added dry, or straight into hot liquid, it clumps instead of dissolving.
Buying guidance
Any plain cornstarch works the same; there's no meaningful quality tier to shop for. Just check that the box or bag is dry and unopened, since it clumps if it picks up any moisture.
Substitutions
- Arrowroot -- thickens similarly and stays clearer, good for a glossy sauce; it can break down if boiled hard for a long stretch, so add it later and keep the heat gentler.
- Potato starch or tapioca starch -- both work as slurry thickeners in roughly the same proportion.
- All-purpose flour -- needs about twice the amount and a few minutes of actual cooking to lose its raw taste, and leaves a cloudier result rather than a glossy one.
Tips & common mistakes
Mix the slurry in a small bowl or ramekin rather than a large one -- with only a tablespoon or two of starch, a bigger container makes it hard to feel out lumps with a finger. Rub or stir the starch into the liquid with a clean finger until it is completely smooth and milk-like, with no dry lumps, no thick sludge sitting at the bottom, and no gummy clumps -- only then combine it with the rest of the liquid. The starch settles out of a slurry within a few minutes of standing, so stir it again just before using if it has been sitting. A cornstarch-thickened sauce can also thin back out if it is boiled hard for too long or reheated repeatedly -- the starch breaks down with extended heat -- so bring it just to a simmer to thicken, then hold it at a lower heat rather than continuing to boil.
Storage
It keeps indefinitely in a sealed container as long as it stays bone dry -- any moisture, even from a damp scoop, causes it to clump into hard lumps that won't fully break down again.