Sauces and Gravies
Thickening the liquids in the pan into a sauce or gravy is often the last step in a recipe, and can be crucial to the success of a dish.
Sauces are made either by stirring a mixture of cornstarch that has been dissolved in an equal amount of water into the liquid and cooking it until it thickens, or by making a sauce or gravy in another pan and pouring it over the dish just before it is served.
Sauces help blend the flavors of all the ingredients, impart an added aroma, and give the dish a shiny, glistening finish.
Chinese recipes usually rely on two kinds of gravies. The first is a mixture of cornstarch, soy sauce or salt, sugar, vinegar, MSG, and a little water. It is usually used for stir-fried and slippery-fried dishes and is added to the pan at the last stage of cooking.
The other way to make gravy is to add seasonings gradually while the dish cooks and to thicken it at the last minute with cornstarch and water. This lets the flavors of the seasonings permeate the food and is generally used with long, low-heat cooking methods.