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

Have you ever tried to twirl a bite of pasta that, by the time it reaches your mouth, seems to have no sauce? Here are some tips on using flour or cornstarch to thicken sauces—items likely already in your pantry. Improve the viscosity of sauces and gravy, so you enjoy their rich flavor in every bite, and make your soups more substantial and filling with this technique.

How to Use Flour to Thicken Sauce

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 cook the flour thoroughly.

How to Use Cornstarch to Thicken Sauce

Using cornstarch to thicken sauce 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.

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 to thicken liquid in a recipe that calls for ¼ cup (four tablespoons) flour, you only need 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.

Other Thickening Agents

There are options other than flour and cornstarch to thicken foods. 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 like baked potato soup and sauces like 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.