How to Thicken a Sauce with CornstarchCornstarch is a common thickening agent in the culinary arts, but if you add it directly to the liquid you want to thicken, it will clump up. To thicken a sauce or soup with cornstarch, you first need to make a slurry, which is a mixture of equal parts cornstarch and liquid (usually water, stock or wine).
It's important to make the slurry with cold liquid, and then add the slurry to the simmering sauce.
Cornstarch imparts a glossy sheen to the liquids it thickens, so it tends to be used more in sweet sauces and pie fillings than in savory sauces and gravies.
- For each cup of liquid you want to thicken, start with 1 tablespoon of cornstarch in a small bowl. Add an equal amount of cold liquid and stir until a smooth paste forms. This is your slurry.
- Whisk the slurry into the hot, simmering liquid that you want to thicken. Bring to a boil and simmer until any starchy taste has been cooked away. Don't cook longer, though, as the starch may break down and the liquid will thin out again.
- If the sauce you are thickening is acidic, you can substitute arrowroot for the cornstarch. Acid makes cornstarch less effective as a thickener. Tapioca starch is another good alternative.
- Conversely, don't use arrowroot to thicken a cream or milk-based sauce as arrowroot combined with milk can produce an unpleasant texture.