Cornstarch

Cornstarch is the starch from the inside of corn kernels, a fine, white, squeaky powder with almost no taste. It thickens sauces, gravies, pie fillings and puddings, makes coatings for fried food crisp, and softens cakes and shortbread. It is gluten free, and it thickens with about twice the power of flour.

How to do it

To thicken a sauce:

1. Mix the cornstarch with an equal or double amount of cold water until smooth. This is a slurry.
2. Bring the sauce to a simmer.
3. Stir the slurry again, then pour it in while stirring.
4. Keep it at a gentle boil for about 1 minute, until the sauce turns glossy and clear and thickens.

As a guide, 1 tablespoon (8 g) thickens about 240 ml (1 cup) of liquid to a medium sauce.

Why it works

Starch granules swell and soak up water as they heat, a process called gelatinization. In cornstarch this happens close to boiling, which is why the sauce only thickens once it bubbles. The swollen granules make the liquid thick and glossy. Stirring hard for a long time, long boiling, or strong acid can break them apart again, and the sauce thins.

How to use it

The same powder has different names:

• Cornstarch in the US and Canada.
• Cornflour in the UK, Ireland, Australia and New Zealand. In the US, corn flour means finely ground cornmeal, which is not the same.
• Maize starch on some ingredient labels.
• Majsstärkelse in Sweden.

In Chinese cooking it coats meat before stir-frying to keep it tender, a method called velveting.

Substitutes

• Potato starch, potatismjöl in Swedish, thickens at a lower temperature and gives a clearer, stretchier result. Use the same amount, and do not let it boil long.
• Arrowroot and tapioca starch work one for one and freeze better.
• All-purpose flour works with twice the amount, cooked a few minutes longer.

How to store it

Keep it in a closed container in a dry cupboard. It keeps for years.

Common mistakes

• Adding the powder straight to hot liquid. It forms lumps at once.
• Not boiling it. The sauce stays cloudy, thin and tastes starchy.
• Freezing sauces thickened with it. They turn spongy and weep when thawed, a result of retrogradation.

In recipes

You will see "1 tbsp cornstarch mixed with 2 tbsp water", "2 tbsp cornflour" and "cornstarch, for dusting".