Baking Is a Chemical Process

• Baking is a delicate chemical process that involves balancing a mixture of two kinds of ingredients: strengtheners, such as flour and eggs, and tenderizers, such as fats and sugar. The process starts the moment the batter or dough is mixed, as liquid reacts with proteins in the wheat to form a sticky substance called gluten. This reaction gives structure to bread, cakes and other baked goods. At the same time, another chemical reaction is taking place: leaveners in the batter or dough react with the liquid to form tiny bubbles of carbon dioxide. These bubbles tend to cling to the gluten matrix and break it down, proving leavening, or lift, to the batter or dough. This is the reaction that creates light fluffiness in baked goods.

Heat Finishes the Process

• An oven puts the finishing touch on this chemical process by providing the heat that melts the ingredients together and dries them into a firm structure. Heat also causes the air bubbles to expand. Interrupting the heat at this point stops the chemical process. With the exception of yeast breads and some custard pies, most baked goods removed from an oven halfway through their baking time won't rise properly and won't finish cooking in the middle.

Partially Baking Breads

• The only instances where "halfway" baking can work is with yeast breads and custard pies. This process is known as "par-baking." With breads, par-baking involves cooking a loaf until it's done on the inside, usually about three-fourths of the way through the cooking time. This partial baking completes the leavening process and sets the structure in the dough, but doesn't give enough time to form an outer crust. The bread is removed from the oven and allowed to cool completely. Baking is finished at a later time. Par-baking works best with crusty breads such as French baguettes or dinner rolls, with Italian rustic breads like ciabatta, foccacia and Tuscan varieties, and with a Mexican-style bread called telera.

Partially Baking Custard Pies

• Par-baking can also work with custard-type pies, such as pumpkin pie, which can be overcooked easily. The trick with custards is to remove the pie before it reaches the "jiggly center" stage that indicates doneness. By removing the pie early, this method also helps avoid cracks from overcooked custard pies. Par-baked pies and breads can be frozen and then finished later.