Cornstarch Substitute

The substitutes and their ratios

Cornstarch thickens by swelling when it hits hot liquid, and several other starches and flours do the same job with different strengths. The one number that matters is how much you need in place of one tablespoon of cornstarch.

Three of those are near one-to-one swaps, which makes them the easy answer when you run out: arrowroot, potato starch and tapioca starch all replace cornstarch in the same measure. Flour is the one people reach for first, and it needs double, because flour is only about 70 to 75 percent starch.

Worked example: thickening 2 cups of sauce without cornstarch

A gravy recipe calls for 2 tablespoons of cornstarch whisked into 2 cups of pan drippings. You have none. Here is what to use instead.

• All-purpose flour: 2 tbsp x 2 = 4 tbsp, which is 1/4 cup
• Arrowroot, potato starch or tapioca: 2 tbsp, unchanged
• White rice flour: 2 tbsp x 2 = 4 tbsp
• Xanthan gum: 2 tsp, whisked into the cold liquid first
• Glucomannan: 1 tsp

The flour route adds 4 tablespoons of a raw grain to your sauce, and raw flour tastes pasty, so cook it for at least 2 minutes after it thickens. A slurry of 4 tablespoons of flour and 1/4 cup of cold water whisked into 2 cups of hot liquid gives a sauce about as thick as heavy cream. If you want it thicker, add more slurry a tablespoon at a time rather than dumping in a second batch.

One habit saves sauces: mix the thickener into cold liquid before it goes near the pan. Dropping dry starch or flour straight into hot liquid makes lumps no whisk can remove. A jam jar with a lid shakes a smoother slurry than a bowl and a fork.

Which substitute for which job

The right swap depends on what you are making, because each starch sets differently once it cools.

Gravies and pan sauces: flour is the traditional choice and gives a matte finish. Arrowroot and potato starch give a glossier sauce, which looks better on a plate but can thin out if you boil it hard or reheat it several times.

Pie fillings: arrowroot and tapioca are the picks. Tapioca gives a slightly stretchy, glossy filling that stands up to fruit acids, while arrowroot stays clear. Flour in a fruit pie needs more oven time to lose its raw taste.

Stir-fries and coating meat: potato starch is the closest match to cornstarch for velveting, the trick of coating sliced meat before it hits the wok, and it fries crisp.

Cold sauces and dressings: the gums win, because they thicken without heat. Xanthan gum at 1 teaspoon per tablespoon of cornstarch is the usual starting point, and a little goes far. Glucomannan gels even faster, so use half as much.

For a stew that simmers for an hour, flour is the safest bet. The long cook time removes the raw flavor, and the starch holds up to heat that would break down arrowroot.

Why cornstarch and flour behave differently

Cornstarch is nearly pure starch, while flour is only about 70 to 75 percent starch with protein and a little fat making up the rest. That difference explains the 2-to-1 ratio: you need roughly twice as much flour to get the same thickening power.

Heat changes them in different ways. Cornstarch granules swell and thicken at around 203°F, and they lose thickening power if you boil them for a long time, which is why a cornstarch sauce can thin out after 10 minutes at a hard boil. Flour thickens more slowly and needs a couple of minutes of cooking to taste right, but it holds up better to long cooking.

Appearance matters too. Cornstarch and arrowroot give a clear, shiny sauce. Flour gives an opaque, cloudy one. Neither is better, but a clear sauce looks right on a stir-fry and wrong on a beef stew, and the reverse holds as well. If you are thickening a dark sauce, a clear thickener keeps the color, while flour will lighten it.

Gluten-free swaps that work

If you cannot use wheat flour, the starches do the job with no changes to the method. Arrowroot, potato starch, tapioca starch and cornstarch are all gluten free, and they swap one for one, so a gluten-free cook who runs out of cornstarch has three direct replacements.

White rice flour is gluten free but a weak thickener, so it needs double the amount, and it leaves a faintly gritty texture. Sweet rice flour, sometimes sold as mochiko, thickens better and is smoother, but it is easy to confuse with plain white rice flour on the shelf. Read the label before you buy.

The gums are the strongest options and the ones to treat with care. Xanthan gum thickens cold liquid on contact and holds a sauce stable through freezing and reheating, which is why it shows up in so many bottled dressings. Use 1 teaspoon in place of 1 tablespoon of cornstarch. Glucomannan, sold as konjac powder, is stronger still, so start at 1/2 teaspoon and add more only if you need it.

The FDA explains how gluten-free labeling works and which allergens a product must declare, and the USDA Food Safety and Inspection Service covers storage and handling for the flours and starches in your pantry.

Too much thickener: the gluey sauce problem

Every one of these thickeners fails the same way when you overdo it: the sauce turns to paste. Starch thickens out of proportion to how much you add, so doubling the thickener does not double the thickness, it turns a sauce into a gel.

If a sauce has gone gluey, thin it with more liquid, stock or water, a splash at a time, and stir over low heat. If you added flour and it tastes raw, keep it at a simmer for a few more minutes. If the problem is a gum, there is no good fix, because xanthan and glucomannan set on contact and do not thin back out with heat. That is the argument for adding them in tiny amounts and waiting before adding more.

A good working ratio for a sauce is 1 tablespoon of cornstarch, or 2 tablespoons of flour, per cup of liquid. That gives a sauce the thickness of heavy cream. For a thin pan sauce, cut it to 2 teaspoons of cornstarch per cup. For a pie filling, use 3 to 4 tablespoons of cornstarch per 4 cups of fruit, depending on how juicy the fruit is. Start at the low end, because you can always thicken a sauce and you cannot easily un-thicken it.