Corn starch is made from the endosperm of the corn kernel. It is one of the most effective thickeners — about twice as effective as flour — and has the benefit of being affordable. But it’s not perfect. It has a few noteworthy limitations. In order to use it like a pro, you will need to be aware of those limitations and what you need to do if you want to get the most from it.
Do make a slurry when using corn starch to thicken a dish.
A slurry is simply a mixture of a powder with a little liquid. Corn starch is a fine powder that will clump up if you attempt to mix it into a hot liquid directly. Mixing it with a little cold water or broth before adding it to a simmering dish will prevent the clumping. For some desserts, a simple syrup may be a better option than plain water for making your slurry.
Do shake rather than stir your slurry.
A corn starch slurry will still clump up when you mix it with cold water, you can get the lumps out by mixing it with whisk or fork but an easier way is to place it in a jar and shake. A few quick shakes will give you a smooth, lump-free slurry.
Do use corn starch in batters and the breading for deep-fried foods.
Corn starch has the ability to evenly transmit heat as one of its most useful and often overlooked properties. The use of corn starch instead of flour — or in a mixture with flour — can greatly limit the potential for scorching or uneven browning. You are far less likely to get darker spots on fried chicken, for example.
Do use corn starch in custards.
Corn starch helps to keep custards from breaking, which is a useful effect when making cheesecakes and quiches.
Do use corn starch if you want a glossy, transparent sauce.
The ability to thicken without making a liquid cloudy and dull-looking is one of the advantages of thickening with corn starch rather than flour.
Do re-stir your corn starch slurry if you mix it ahead of time.
Corn starch will separate from the water if it sits for too long.
Don’t use corn starch when you are thickening highly acidic liquids.
Corn starch is not the most reliable thickener for sauces that contain a lot of lemon juice or vinegar. It might work if the acidity is low enough, but you will be taking a risk. If it doesn’t work, you might wind up with a chalky-tasting sauce that is almost as watery as it was without the addition of corn starch. Depending on how much corn starch you added, you might find it unpalatable.
Don’t over-stir corn starch.
Over-stirring can affect the thickening reaction and keep corn starch from thickening your dish, even when you add a lot of it. Corn starch granules work by absorbing and trapping water. Too much stirring can break the bonds that trap the water, which causes the corn starch to lose its thickening ability. Once a sauce with corn starch begins to set, keep stirring to a minimum.
Don’t overcook corn starch.
Cooking for too long will thin out a liquid thickened corn starch.
Don’t freeze sauces thickened with corn starch.
Corn starch thickened sauces will turn spongy after they are thawed.