When hydration occurs, water is absorbed and the chemical changes necessary for structure and texture development can take place.
Liquids contribute moistness to the texture and improve the mouthfeel of baked products.
When water vaporizes in a batter or dough, the steam expands the air cells, increasing the final volume of the product. Milk contributes water and valuable nutrients to baked goods. It helps browning to occur and adds flavor. When making yeast dough, milk should be scalded and cooled before adding to other ingredients. This is done to improve the quality of the dough and the volume of the bread.