Thickening agents such as corn starch and flour can be used to thicken sauces and gravies.
There is nothing worse than making a soup or sauce and realizing that it is too thin. If you run into this problem, you might wonder what type of thickener is best. Cornstarch and all-purpose flour are two thickeners that most people have in their kitchens, and you can use them to thicken a wide variety of soups and sauces. However, there are differences between the two.
Uses: Cornstarch and all-purpose flour are both useful for thickening creams, sauces and gravies. Cornstarch is best for thickening dairy sauces. When you are thickening with flour, mix 1 tbsp. of flour with 1/2 cup of warm water before you add the mixture to your food. Be sure to bring your sauce to a full boil after adding the flour mixture. Also mix flour with butter or another fat to make a roux. If you are cooking with cornstarch, dissolve 1 tbsp. of cornstarch into 1/2 cup of cold water. Add this mixture to your sauce and bring it to a boil for about a minute. Do not boil it any longer than that or the cornstarch will break down and the flavor will be off.
Texture: If you have trouble with lumpy gravy after using a flour thickener, put it in a blender to smooth out the lumps or strain the lumps out. Be sure not to cook your sauce too long after adding the flour or it may get lumpy. Stir it continuously with a whisk in order to break up any lumps that try to form. Also, if your cornstarch sauce or gravy gets lumpy, strain it or use a blender.
Final Results: When you use flour to thicken a sauce, your final product will be either cloudy or white. This is not an issue if you are making a white sauce or a cream soup; it should not taste like flour if you cook it sufficiently afterward. If you are using cornstarch, your final result will be slightly cloudy but smooth and slightly shiny. This is an excellent choice for custards or creams, when you want the final result to be a bit shiny.
Storage: A final factor that should affect your choice of cornstarch versus flour for a thickener is storage. If you plan to refrigerate your food after you cook it, a flour sauce may get very thick and gummy. It sometimes helps to add milk or water to the sauce when you reheat it. On the other hand, cornstarch sauces do not freeze well, so you will need another thickener if you plan to freeze your final result.