During proofing, yeast converts glucose and other carbohydrates to carbon dioxide gas which gives the bread rise and alcohol which gives it flavor. Bacteria which coexist with the yeast consume this alcohol, producing lactic and acetic acids. Different types of bread have vastly different requirements for proofing depending on their recipe. Some breads will only require a single proofing while others will need multiple periods. Between stages of proofing recipes will often instruct a cook to "punch down" or "deflate" the dough to allow the bubbles of gas which have formed in the dough to deflate without popping (called overproofing). Length of proofing periods can be determined by time or characteristics. Often the "poke method" is used to determine if a bread has risen long enough; if the bread, when poked, springs back immediately it is underproofed and needs more time.
Proofing is divided into a number of different categories including fermentation, proofing, retarding, autolyse. Fermenting is any stage of proofing which is completed prior to the shaping of the bread. Often a third of a bread's rise will occur during this stage. Proofing is the general term for allowing a bread to rise while at room temperature after it has been shaped. Retarding is the stage in which bread is placed into a dough retarder, refrigerator, or other cold environment to slow the activity of the yeast. The retarding stage is rarely found in recipes with commercial yeast but often used in sourdough bread recipes to allow the bread to develop it characteristic flavor. Autolyse is a period of rest allowed for dough to relax. After the initial mixing of flour and water, the dough is allowed to sit. This rest period allows for better absorption of water and allows the gluten and starches to align. Breads made with autolysed dough are easier to form into shapes and have more volume and improved structure.
A dough proofer is a chamber used in baking that encourages fermentation of dough by yeast through warm temperatures and controlled humidity. The warm temperatures increase the activity of the yeast, resulting in increased carbon dioxide production and a higher, faster rise. Dough is typically allowed to rise in the proofer before baking.
A dough retarder is a refrigerator used to control the fermentation of yeast when proofing dough. Lowering the temperature of the dough produces a slower, longer rise with more varied fermentation products, resulting in more complex flavors. In particular, cold reduces the activity of the yeast relative to the lactobacilli, which produce flavoring products such as lactic acid and acetic acid.
A banneton is a type of basket used to provide structure for the sourdough breads during proofing. Proofing baskets are distinct from loaf pans in that the bread is normally removed from these baskets before baking. Traditionally these baskets are made out of wicker, but many modern proofing baskets are made out of silicone or plastic. Frequently a banneton will have a cloth liner to prevent dough from sticking to the sides of the basket - though some have no such cloth. These baskets are used both to provide the loaf with shape and to wick moisture from the crust. Banneton baskets are also known as Brotform or proofing baskets. Alternatively, a couche or proofing cloth can be used to proof dough on or under. Couche are generally made of linen or other coarse material which the dough will not stick to and are left unwashed so as to let yeast and flour collect in them, aiding the proofing process.