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How to Thicken Cornstarch in the Microwave

Jenny Harrington

Cornstarch, a derivative of corn, provides a quick and effective thickener for sauces, soups and gravies. It's also used to thicken puddings and dessert fillings. The cornstarch dissolves readily in cold water, but it begins to gel and thicken as it heats.

Cornstarch added directly to a hot liquid clumps and doesn't thicken properly. You can prepare many cornstarch-based recipes in the microwave, but some experimentation is necessary to ensure you can adapt your favorite stovetop recipes to microwave cooking successfully.

  1. Combine 1 part cornstarch with 2 parts cold water in a microwave-safe bowl. Use ½ tablespoon cornstarch for every ½ cup of liquid you are thickening. Whisk the cornstarch and water together until the starch is dissolved in the water and the water looks milky.

  2. Whisk in the remaining liquid for the recipe, typically broth or milk if you are making a sauce, soup base or gravy.

  3. Heat the mixture in the microwave for three minutes on the high power setting. Stir well after heating.

  4. Cook at high power for an additional two minutes, or until the mixture begins to boil. Allow the mixture to boil for one full minute.

  5. Remove the bowl from the microwave promptly at the end of the cooking time. Stir in any remaining seasonings before serving.


Dessert recipes may require more exacting preparation steps to thicken properly. Use a recipe specifically made for microwave cooking when preparing puddings, custards and fruit sauces with cornstarch.


Do not boil cornstarch for more than one minute, because overcooking can cause the mixture to break up and lose its thickening power.