Although flour is the traditional thickening agent in most cooking, cornstarch, also known as cornflour, is a fine, powdery flour ground from the endosperm, or white heart, of the corn kernel. People often wonder what the difference is between cornstarch and flour. Both are starches, but cornstarch is pure starch, while flour contains gluten. The gluten reduces the thickening power of flour, so lacking gluten, cornstarch has twice the thickening power of flour. Sauces thickened with cornstarch will be clear, rather than opaque, as with flour-based sauces, and it doesn't cause lumps like flour.

How To Cook With Corn Starch

What are the advantages of using corn starch rather than flour? Corn starch has twice the "thickening power" of flour, so it's necessary to use only half as much. Example: If recipe calls for 1/4 cup of flour, use just 2 tablespoons corn starch. Corn starch thickens with a satiny smoothness and glossy appearance. It adds no taste of its own to mask the flavor of foods.

Recipes thickened with corn starch have a brighter, more translucent appearance than those thickened with flour. Corn starch also blends more easily with liquids than flour because it doesn't absorb liquid until it's cooked.  Cooking with corn starch is easy when you follow a few simple guidelines. Gradually stir cold liquids into corn starch until completely smooth, cook over medium-low heat. Cooking over high heat can cause lumping, but avoid stirring too vigorously because it may break down and thin out.. Stir gently during while it thickens, the starch granules will have swelled to their full capacity in about 1 minute.

Using Cornstarch As A Thickener

Always mix a slurry of cornstarch and a small amount (1/4 cup) of cold liquid (water, stock, wine, etc.) until smooth, then add this mixture to the food that you want thickened. Do not mix with liquids that are acid such as citrus juice or apple juice or it's thickening power is cut in half. Do not boil a cornstarch thickened sauce or it will thin out.

As as rule, I use 1 tablespoon of cornstarch to thicken every 2 cups of liquid to a medium consistency. Cornstarch mixed a little cold liquid, is stirred into the hot food during the final stage of cooking, and it must be cooked to 203°F (95°C) before thickening begins. At that point, it usually thickens fairly quickly and the sauce turns from opaque to transparent, but sauces will thin if cooked too long, boiled or stirred too vigorously.

Are There Any Problems With Using Cornstarch?

Corn starch mixtures that don't thicken at all, or thicken and then thin out during cooling are disappointing. One or more of the following may have caused the problem.

Too Little Liquid: If there is not enough liquid (water, milk, juice) in the mixture, the corn starch granules will not fully swell and remain thickened when the mixture cools. Adding a little more liquid (not more corn starch) is likely to solve the problem.

Too Much Sugar: A higher proportion of sugar than liquid (water, milk, juice) in a mixture can interfere with the swelling of the corn starch granules and prevent thickening during cooking and/or cause thinning during cooling. Adding more liquid (not more corn starch) will often solve the problem.

Too Much Fat: An excessively high proportion of fat or egg yolks in a mixture can interfere with the swelling of the corn starch granules and prevent thickening during cooking and/or cause thinning during cooling. Adding more liquid (not more corn starch) will usually solve the problem.

Too Much Acid: Acid ingredients such as lemon juice, lime juice or vinegar will reduce the thickening ability of the starch or prevent the mixture from thickening. Increase the starch level slightly or stir acid ingredients in after cooking.

Too Much Stirring: Excessive or rough stirring with a wire whisk or even a spoon may break the starch cells and cause the mixture to thin out.

Excessive Cooking: Simmering or boiling a corn starch thickened mixture for an extended period of time may cause the starch cells to rupture and the mixture to thin.

Freezing: Freezing corn-starch thickened mixtures will rupture the starch cells and cause the mixture to thin out.

 Uses For Cornstarch

Cornstarch is often used in Oriental recipes because it results in a lighter, more clear gravy with a glossy sheen. Besides thickening, cornstarch helps to prevent eggs from curdling—certainly helpful in making custards, flans,cheesecakes, quiche and other egg dishes. It also causes heat to be transmitted more evenly throughout the dish, and can be used to make a glaze. Cornstarch can be used to "flour" pieces of meat for added crispiness when browning. It is the best choice for thickening dairy-based sauces, and it is also used in making custards, gravies and other sauces.