Brittles always contain some form of nuts or seeds as an integral part of the formula. Toffee and caramels may also contain these ingredients. Aside from flavor and texture, nuts contribute the proteins that are required for Maillard browning, resulting in the development of caramelized flavors. When nuts are added late in cooking, or after the completion of cooking, they do not contribute to browning and are added solely for flavor and texture. Nuts are high in fat, and so they also contribute to richness.