How starch thickens sauce
In hot liquid, starch granules absorb water, swell and crowd together, which thickens the sauce. For a medium-thick sauce, use about 1 tablespoon of cornstarch per cup (240 ml) of liquid.
Bring it to a gentle boil
Thickening starts around 60 to 70°C. Cornstarch reaches full thickness near a gentle boil, about 95°C. Flour needs a few more minutes at that heat to lose its raw taste. Keep stirring.
Choosing a starch
Cornstarch makes an opaque, glossy sauce. Arrowroot stays clear and freezes well, but turns slimy with milk. Flour makes a creamy, opaque gravy and needs a few minutes of cooking to lose its raw taste.
Test yourself
Questions from the interactive lesson, with the answer and the why.
Fill the blank: To prevent lumps, mix cornstarch with ___ water before adding it to a sauce.
To prevent lumps, mix cornstarch with cold water before adding it to a sauce. In cold water the granules spread out and none swell, so they cannot clump.
True or false: A cornstarch slurry stirred into lukewarm sauce at 40°C won't thicken it yet.
True. Starch granules need about 60 to 70°C to swell, so the sauce needs more heat.
A cornstarch gravy was thick, but after 10 more minutes of hard boiling and stirring it is thin. Why?
Boiling tore the granules apart. Swollen granules are fragile. Long hard boiling and stirring tear them open.
What went wrong? You dump dry cornstarch straight into a simmering pot. Lumps form right away.
Dry starch hit hot liquid. The outside of each clump gels and traps dry starch inside.
You want a clear, glossy fruit sauce that survives the freezer. Which thickener fits best?
Arrowroot. Arrowroot cooks clear and holds its texture through freezing and thawing.
Thickening with cold vs hot starch
Lumps are a choice.
Do the 15-minute experiment
