Corn starch, sometimes referred to as corn flour, is a carbohydrate extracted from the endosperm of corn. This white powdery substance is used for many culinary, household, and industrial purposes. In the kitchen, corn starch is most often used as a thickening agent for sauces, gravies, glazes, soups, casseroles, pies, and other desserts.
Because corn starch is made from corn and only contains carbohydrates (no protein), it is a gluten free product. For this reason, corn starch is an excellent gluten free alternative to flour thickeners in recipes. Be sure to check the packaging to make sure your corn starch has not been produced in a facility that also processes wheat products, to prevent the possibility of cross contamination.
How is Corn Starch Used?
Corn starch can be mixed into cool or room temperature liquids and then heated to cause a thickening action. Corn starch is often preferred to flour as a thickener because the resulting gel is transparent, rather than opaque. Corn starch is also relatively flavorless compared to flour and provides roughly two times the thickening power. Corn starch can be substituted at half the volume of flour in any recipe that calls for flour as a thickening agent.
Corn starch can also be used to coat fruit in pies, tarts, and other deserts before baking. The thin layer of corn starch mixes with the fruit juices and then thickens as it bakes. This prevents pies and other desserts from having a watery or runny texture.
Corn starch is also used as an anti-caking agent. Shredded cheese is often coated with a thin dusting of corn starch to prevent it from clumping in the package. The corn starch will also help absorb moisture from condensation and prevent a slimy texture from developing. A small amount of corn starch is often mixed into powdered sugar for the same purpose.
How Does Corn Starch Thicken?
Corn starch is comprised of long chains of starch molecules, which when heated in the presence of moisture, will unravel and swell. This swelling action, or gelatinization, is what causes the thickening to occur.
Tips for Using Corn Starch
Corn starch should not be added straight into a hot liquid as this can cause it to clump and form lumps. Corn starch should first be mixed into a room temperature or slightly cool liquid to form a slurry, and then stirred into the hot liquid. This will allow for even distribution of the corn starch molecules before they have a chance to swell and gelatinize.
Mixtures containing corn starch should be brought to a full boil before cooling. Under heating corn starch mixtures can cause them to seep moisture or become thin again upon cooling. The mixture may appear thickened after a slight heating, but if the starch molecules are not fully gelatinized, they will release the moisture once cooled.
Sauces and other mixtures thickened with corn starch should not be frozen. Freezing will break down the gelatinized starch matrix and the mixture will become thin after thawing.
How to Store Corn Starch
Because corn starch absorbs moisture, it is critical to keep it in an air-tight container where it will not be exposed to ambient humidity. Corn starch should also be kept away from extreme heat. Store your corn starch in a sealed container and in a cool, dry place. When stored properly, corn starch will last indefinitely.