When perusing Chinese stir-fry recipes, you may have noticed many include cornstarch in the marinade. (Chinese stir-fries generally include a marinade as well as a sauce.) Adding a starch to the marinade before stir-frying is a common Chinese cooking technique. The starch binds together the liquid ingredients in the marinade and seals them to the meat, poultry, or seafood that is being marinated. This technique is particularly important in quick-cooking stir-fry dishes as it helps give the food more flavor. The cornstarch also seals in the juices of the meat and makes the protein crispy.
An added advantage of using starch in a marinade is that it helps thicken the liquid ingredients in the stir-fry dish, meaning you may not need to add a sauce in the final stages of cooking. But many Chinese stir-fry recipes do include a sauce, and cornstarch is always an ingredient. An added bonus is that the cornstarch creates a glossy finish to the marinade and sauce.
What Cornstarch Is
Made from the endosperm of corn (the part of the seed that stores starch), cornstarch is commonly used in marinades (and sauces) because it is readily available at most supermarkets. However, in China, tapioca starch, water chestnut starch, or a combination of the two is commonly used. You can also use arrowroot starch if desired.
Cornstarch in Marinades
There are a few tips for using cornstarch in recipes, and a stir-fry is no exception. When a Chinese recipe calls for cornstarch in the marinade, always add it last unless the recipe specifically calls for blending it with the other ingredients before adding it to the food being marinated. You also want to make sure the cornstarch is blended well so there aren't any lumps.
A Cornstarch Slurry
After the ingredients are marinated and stir-fried (which often happens in stages and perhaps more than once), they are finished with a sauce, which is usually thickened with cornstarch. But simply adding cornstarch to the sauce can cause the mixture to clump up, so a "slurry" needs to be made first. A cornstarch slurry is a mixture of equal parts cornstarch and a cold liquid, such as water or broth. The mixture then needs to be stirred until it becomes a smooth paste. The slurry is added to the wok with the other ingredients for the sauce—the wok needs to be hot to create the correct consistency, but not too hot that it turns the sauce into a gluey mass.
Chinese Recipes Using Cornstarch
A true Chinese stir-fry will have cornstarch (or other starch) on the ingredient list, and honey beef with sesame seeds is a great example. Flank steak is stir-fried in a sweet and tangy sauce of honey and soy sauce, accented with oyster sauce and sprinkled with sesame seeds. Or try this beef and vegetable stir-fry recipe that includes bok choy, mushrooms, and red onion. Make better-than-takeout with this recipe for cashew chicken—the flavors of ginger, hoisin sauce, and garlic turn a simple dish into something special. Or make a chicken stir-fry with bok choy and garlic sauce to add some excitement to dinnertime.