How to Use Corn Starch Instead of Flour
Corn starch can replace flour as a thickener, but you usually need less of it. The method also changes because starch should be mixed with cold liquid before it reaches the hot pan.
Know which ingredient you need
Corn starch is the fine white starch taken from maize and is often labelled cornflour in the UK. It is different from maize flour, which contains more of the whole grain and does not thicken in quite the same way.
This substitution works best when flour is being used to thicken a sauce, soup, gravy or filling. Corn starch is not a straightforward replacement for flour in bread, cakes or pastry because flour also provides structure.
Use a smaller amount
Corn starch has stronger thickening power than plain flour, so a useful starting point is about half as much. For example, if a recipe calls for two spoonfuls of flour, begin with one spoonful of corn starch, then adjust if needed.
The ideal amount depends on the dish and your preferred consistency. Sauces containing more liquid may need extra starch, while a filling that thickens as it cools may need less than it first appears.
Make a smooth slurry
Put the corn starch in a small bowl and stir in a little cold water or another cold liquid from the recipe. Mix until smooth, as adding dry starch directly to a hot pan can create stubborn lumps.
Pour the slurry slowly into the hot dish while stirring. Let it heat gently until the liquid thickens, but avoid prolonged vigorous boiling because the texture can become thinner again.
Account for the change in your food log
Record the amount of corn starch you actually use rather than the flour quantity written in the original recipe. If you track by weight, weigh the starch before mixing it with liquid and use the nutrition information from its label.
Changing the thickener can alter the carbohydrate, protein and energy totals for the full recipe. Divide the updated recipe total by the number or weight of portions you serve, as the exact result depends on your ingredients and serving size.