Curdling

In cookery, curdling is the breaking of an emulsion or colloid into large parts of different composition through the physico-chemical processes of flocculation, creaming, and coalescence. Curdling is intentional and desirable in making cheese and tofu; unintentional and undesirable in making sauces and custards.

Cheese and tofu

Main article: Cheese

Main article: Tofu

Milk and soy milk are curdled intentionally to make cheese and tofu by the addition of enzymes (typically rennet), acids, or various salts (magnesium chloride, calcium chloride, or gypsum); the curds are then pressed.

Egg sauces

In hot preparations emulsified with eggs like hollandaise and custard, curdling is the undesirable result of overheating the sauce. Sauces which contain starch curdle with more difficulty.

In cold sauces like mayonnaise as well as in hot sauces, too large a ratio of fat to egg may also cause curdling.

Milk sauces

In sauces which include milk or yoghurt, overheating often causes curdling. The higher the fat content, the less likely curdling is. Strained yoghurt used in sauces also curdles only with difficulty.

Bibliography

• Harold McGee, On Food and Cooking: The Science And Lore Of The Kitchen, 1984-2004.