Curdling
Curdling is the breaking of an emulsion or colloid into large parts of different composition through the physio-chemical processes of flocculation, creaming, and coalescence. Curdling is purposeful in the production of cheese curd and tofu, but undesirable in the production of a sauce, cheese fondue or a custard.
Method
In curdling, the pH of the milk decreases and becomes more acidic. Independently floating casein molecules attract one another, forming "curdles" that float in a translucent whey. At warmer temperatures, the clumping reaction occurs more quickly than at colder temperature. Curdling occurs naturally if cows' milk is left open in a warm environment to air for a few days.Cheese and tofu
and soy milk are curdled intentionally to make cheese and tofu by the addition of enzymes, acids, or various salts ; the resulting 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.