High Heat Will Curdle Milk, Cream

Q: Please explain why when I add cream to a dish to make a sauce it often curdles. Sometimes I substitute half-and-half - is that the problem? Or is it related to the temperature at which the dish is being cooked?

A: Temperature is certainly important. When you add cream to any dish cooked on top of the stove, it will curdle if the mixture is permitted to boil. Always heat dishes containing cream over a low heat, stirring often.

A major cause of curdling in cooking milk products is cooking over too high a heat and for too long a time, according to authors Sylvia Rosenthal and Fran Shinagel in ``How Cooking Works'' (Macmillan; 1981). They go on to say: ``There is also a danger of curdling if you add a milk product to an acid food. But if you reverse the process and add the acid food slowly to the milk, you prevent curdling.''

Q: Does a slow cooker destroy any of the nutrients in food?

A: Yes, some nutrients are destroyed by lengthy cooking, according to Roberta Phillips, home economist for Rival Mfg. Co. On the other hand, some nutrients are retained by slow cooking.

Nutrients affected by length of heating include proteins and vitamins, particularly some of the B vitamins, such as thiamine. If the cooking liquid is consumed with the food, water-soluble vitamins are