How to Measure the Ratio of Flour Vs. Cornstarch Substitute

Precise measurements are critical when substituting corn starch for flour.
Precise measurements are critical when substituting corn starch for flour. (Image: John Foxx/Stockbyte/Getty Images)

Cornstarch is an effective, quick and efficient substitute for flour-based thickening agents. Flour-based thickeners, such as roux and beurre manie, require approximately 30 minutes of simmering for the starch granules to gelatinize – the process that prompts them to swell and thicken the sauce or soup. Cornstarch, however, thickens after only a few seconds when added to a liquid with a minimum temperature of 203 degrees Fahrenheit – a temperature usually reached with the medium setting on a stovetop. Cornstarch thickeners, commonly referred to as slurries, give sauces and soups a velvety finish, an appealingly glossy appearance, and serve as an ideal substitute for flour.

Things You'll Need

  • Measuring cups
  • Measuring spoons
  • Cornstarch
  • Water

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Find the amount of flour needed for the preparation.

Divide the amount of flour called for in half by volume. For instance, if the recipe calls for 2 tbsp. of flour, measure 1 tbsp. of corn starch.

Mix the corn starch with an equal amount of water by volume. For example, if you're thickening a sauce with 1 tbsp. of corn starch, mix it together with 1 tbsp. of cold water to form a slurry.

Whisk the slurry vigorously into the sauce or soup to prevent lumps.


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