Double boilers are used to gently cook delicate, dry ingredients. They work by creating a hot water bath in the bottom pan and the food in the top pan is effectively cooked by the heat of the water in the bottom pan. It is a slow process that is generally used when melting chocolate or sugars to create desserts. Double boilers are designed to be used for working with extremely delicate ingredients such as chocolate or eggs that cannot be mixed with water. The water bath in the bottom pan warms the food in the upper pan, slowly cooking or melting the ingredients. Because many of the foods used in these pans cannot come into contact with water, it is imperative to remember not to put a cover on the pan as they are cooking. The condensation from the water will drip into the ingredients and ruin the recipe.