Cornstarch is typically "cooked" as a thickening agent in sauces, gravies, soups, and stews by first creating a slurry and then incorporating it into the hot liquid. Here's the proper method:
Making a Cornstarch Slurry
This is the most crucial step to prevent clumping.
- Combine: Mix cornstarch with a small amount of cold water. Use about half the amount of cornstarch as you would flour for a similar thickening effect.
- Ratio: A common starting point is 1 tablespoon of cornstarch to 2 tablespoons of cold water.
- Mix Thoroughly: Stir until the mixture is completely smooth and no lumps remain. This is your cornstarch slurry.
Incorporating the Slurry
- Gradually Add: Slowly pour the cornstarch slurry into the hot liquid you want to thicken, stirring constantly.
- Stir Continuously: Keep stirring to ensure the slurry is evenly distributed and doesn't settle at the bottom.
- Bring to a Boil: Continue stirring and bring the liquid to a gentle boil.
- Boil Briefly: Once boiling, cook for about 1 minute, still stirring. The mixture will thicken as it cooks.
- Adjust Consistency: If the sauce becomes too thick, add more liquid. If it's not thick enough, mix a little more cornstarch slurry (1 tsp cornstarch + 2 tsp cold water) and add it to the sauce, cooking and stirring as before.
Important Considerations:
- Cold Liquid is Key: Always mix cornstarch with cold water first. Using hot liquid will cause the cornstarch to clump instantly.
- Overcooking: Prolonged boiling or overcooking can cause the cornstarch to break down and lose its thickening power.
- Acidity: Acidic ingredients like lemon juice or vinegar can also interfere with cornstarch's thickening ability. Add them after the sauce has thickened.
- Storage: Sauces thickened with cornstarch don't always reheat well. They may become thin or watery.
