How to Thicken Sauce, Gravy, and Soup with Cornstarch or Flour

Have you ever tried to twirl a bite of pasta that, by the time it reaches your mouth, seems to have no sauce? Or maybe you pour turkey gravy over meat and potatoes, only to have it spread over the entire plate? If so, you understand the importance of how to thicken sauce.

You want to serve up sauces with the correct viscosity to cling to the intended food, not run everywhere. Here are some tips on how to thicken sauce with cornstarch and flour—items likely already in your pantry so that you don't have to run to the store.

How to Thicken Sauce with Flour

To use flour as a thickening agent:

1. Use two tablespoons flour mixed with ¼ cup cold water for each cup of medium-thick sauce.
2. Thoroughly mix in the water to prevent lumps.
3. After stirring the combined flour and water into the sauce, cook and stir over medium heat until thickened and bubbly.
4. Heat one minute more to thoroughly cook the flour.

How to Thicken Sauce with Cornstarch

Thickening a sauce with cornstarch is very similar to using flour, but you need different quantities:

1. Use one tablespoon cornstarch mixed with one tablespoon cold water (aka a cornstarch slurry) for each cup of medium-thick sauce.
2. thoroughly mix the cornstarch and water together, then pour into your sauce.
3. Cook and stir over medium heat until thickened and bubbly.
4. Heat two minutes more in order to completely cook the cornstarch.

Test Kitchen Tip: Be careful not to overcook cornstarch-thickened sauces. They can break down when overcooked (the starch loses its thickening properties when cooked too long).

Substituting Cornstarch for Flour as a Gluten-Free Alternative

If you have someone in the family with an allergy restriction, you may need a gluten-free thickener for your soup recipe. It's important to note that cornstarch has twice the thickening power of flour. If you need to substitute cornstarch in a gravy recipe that calls for ¼ cup (four tablespoons) flour, you would only need to use two tablespoons cornstarch. If you're substituting flour for cornstarch to thicken the sauce in your recipe, substitute two tablespoons all-purpose flour for every one tablespoon cornstarch.

Note: Our Test Kitchen does not recommend freezing cornstarch thickened mixtures as the freezing process breaks down the starch thickening properties.

Other Thickening Agents

Flour and cornstarch aren't your only options to use as a food thickener. When it comes to thickening soup and other sauce-based recipes, you can make a roux (a mixture of flour and fat). This is common for creamy soups such as baked potato soup and sauces such as macaroni and cheese. (Get the full instructions on how to make roux here.)

Depending on your recipe, you can use eggs, a roux, or a puree of ingredients for a liquid thickener. The soup thickener depends on the recipe because some thickening agents can affect the soup's flavor.

Put those thickening skills to good use by making chicken marsala for dinner or a delicious turkey gravy for your Thanksgiving feast. You can also make some sweet additions to your menus with a raspberry-rhubarb waffle topper or lemon curd.