Tempering is a term used in cooking when an ingredient—or two—needs to be stabilized, meaning its characteristics remain the same and aren't altered in any way. We see this technique used when combining ingredients that are each at completely different temperatures. In the kitchen, for instance, when a hot liquid like soup or stock is mixed directly with a cold item like cream or sour cream or eggs, the cold product will tend to curdle as the soup's heat coagulates the proteins in the dairy. Tempering is used to avoid this from happening.
The tempering technique is also utilized when adding melted chocolate to other ingredients to prevent it from seizing, but this should not be confused with the method of tempering chocolate in candy making; chocolate is tempered by heating and cooling and heating again to stabilize the fat in the chocolate so it achieves a shiny appearance and doesn't crystallize or "bloom" once it cools.
How Tempering Works
Tempering slowly increases—they key word here being "slowly"—the heat of the cold ingredient so its temperature gradually rises and becomes more compatible with the temperature of the hot ingredient (which essentially slowly cools down when it comes in contact with the cold food). The shock of a cold ingredient suddenly turning hot can cook and change its composition, making it cook too quickly, curdle, seize, break, lump up, or split.
How to Temper
Tempering is most often called for in a recipe when you are making a sauce, ice cream, custard, some cream soups, and recipes including sour cream. The general technique is to add a small amount of the hot liquid to the cold ingredient. This can be done by placing the cold item in a heatproof bowl and then briskly whisking in a few ladles of the hot ingredient and mixing or whisking until combined. Then you need to add the tempered mixture into the rest of the hot liquid.
For example, if your recipe requires you to combine hot milk with eggs (like in a pastry cream), you need to slowly add a small amount of the hot milk to the eggs and whisk until combined. Then you will take this mixture and add it to the hot milk and whisk. (If you simply added the eggs to the hot milk you would end up with scrambled eggs in milk.)
Recipes with Tempered Ingredients
If you would like to try your hand at this tempering technique, there are both savory and sweet recipes calling for the method. Recipes including sour cream, such as mushroom-barley soup and meatballs in sour cream-mushroom sauce require tempering the cold sour cream with hot liquid. For a dessert recipe that can be used in a myriad of ways, a versatile vanilla pastry cream is ideal for learning to temper as well as a great recipe to have under your belt. And master the temper with a classic chocolate ice cream—everyone will thank you!