Overview
The dry heat of baking changes the form of starches in the food and causes its outer surfaces to brown, giving it an attractive appearance and taste. The browning is caused by caramelization of sugars and the Maillard reaction. However, the moisture is never entirely "sealed in"; over time, an item being baked will become dry. This is often an advantage, especially in situations where drying is the desired outcome, like drying herbs or roasting certain types of vegetables. The most common baked item is bread. Variations in the ovens, ingredients and recipes used in the baking of bread result in the wide variety of breads produced around the world.
Some foods are surrounded with moisture during baking by placing a small amount of liquid (such as water or broth) in the bottom of a closed pan, and letting it steam up around the food, a method commonly known as braising or slow baking.
When baking, consideration must be given to the amount of fat that is contained in the food item. Higher levels of fat such as margarine, butter or vegetable shortening will cause an item to spread out during the baking process.
With the passage of time breads harden; they become stale. This is not primarily due to moisture being lost from the baked products, but more a reorganization of the way in which the water and starch are associated over time. This process is similar to recrystallization, and is promoted by storage at cool temperatures, such as in a domestic refrigerator.
Read more about this topic: Baking