Cornstarch is a fine, nearly pure starch extracted from the endosperm of corn kernels. It is widely used in professional kitchens to thicken sauces, soups, custards, puddings, pie fillings and fruit preparations. In the United Kingdom and some other markets, cornstarch is called cornflour; this is different from North American cornmeal or finely ground whole corn.
When mixed with cold liquid and heated, cornstarch granules absorb water, swell and release starch molecules that thicken the surrounding liquid. This process is called starch gelatinization. The sauce becomes more viscous as it heats, but excessive stirring or prolonged boiling can weaken the thickened structure.
Cornstarch is used to thicken stir-fry sauces, fruit pie fillings, pastry cream and puddings. It is also used in dry coatings for fried foods, where it can contribute a crisp surface when combined with other ingredients.
Cornstarch has greater thickening power by weight than wheat flour and produces a relatively glossy, translucent finish. Flour contains protein and other components as well as starch, so it creates a more opaque result and generally requires longer cooking to remove its raw flavour. Arrowroot can produce a clearer gel and is often preferred for some acidic fruit sauces, while cornstarch is more widely used for custards and general-purpose thickening.
Chef’s tip: Always make a slurry with cold liquid before adding cornstarch to a hot sauce. Adding dry starch directly to hot liquid can create lumps. Remember that acidic ingredients, freezing and prolonged heat can affect the final texture.
Key distinction: Cornstarch is a purified corn starch used for thickening; cornmeal is ground whole corn and is not a direct substitute.
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