Liquids

When you combine milk, water, or any other liquid with beaten eggs, it dilutes and separates the protein molecules, which makes it difficult for them to join. In turn, this raises the coagulation temperature and slows the thickening process. When the eggs are combined with milk (with the possible addition of sugar), a stirred custard can be brought to 71°C (160°F) before it will curdle. One whole egg or 2 egg yolks will barely set 240 milliliters (1 cup) of milk. Making a firmer custard requires more protein, usually 3 whole eggs per 475 milliliters (2 cups) of milk. The rate at which a liquid conducts heat also affects the cooking time. For instance, homogenized whole milk conducts heat more slowly than skim or nonfat milk and therefore takes longer to cook.