How to Measure the Ratio of Flour Vs. Cornstarch Substitute

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.