baking bread

Baking


What is Baking?

Baking in the oven is the final step of making a loaf of bread. Formation of a satisfactory crust with optimum thickness and characteristics is one of the most important aspects of baking. Once the crust has formed, it creates a physical barrier to inhibit further expansion of the dough piece. The center of the dough piece continues to expand until it meets the crust and the pans.

Function

In the oven, the center of the bread goes through a complex progression of physical, chemical and biochemical changes. Caramelization and the Maillard reaction are two major thermal chemical reactions that occur during baking, contributing to the browning of the crust and the flavor and aroma of bread. During the baking process, starch gelatinization occurs at about 75 ℃ (167 ℉). The starch granules would absorb any free water in the dough, causing an increase in the viscosity of the continuous phase of the dough.  This progression causes the bread crumb structure to stabilize.

Enzyme activity is limited in the baking stage.  Alpha-amylase is responsible for converting starch into sugars, providing the food for yeast and causing the dough to become more fluid, hence promoting dough expansion. The activity of fungal alpha-amylase is deactivated at 60 ℃ (140 ℉), lower than other types of alpha-amylase, such as G4-amylase and maltogenic alpha amylase, in which activities are deactivated at 75 ℃ (167 ℉). Cereal alpha-amylase is deactivated at 85℃ (185 ℉) and bacterial alpha amylase deactivated at 90 ℃ (194 ℉).

Since yeast activity is the main contributor to the gas production, yeast activity decreases as the dough warms up and is inactivated when the temperature reaches 56 ℃ (132 ℉).  The protein structure is set after starch gelatinization as gluten denatures at about 75 ℃ (167 ℉). The gluten films are denatured and transformed to a semi-rigid structure by interaction with the swollen starch.

Application

The final core temperature usually determines the loaf quality.  A core temperature of 92-95 ℃ (198-203 ℉) is the usual final bread temperature as it exists the oven. Having a glossy crust on the loaf comes from the first few seconds of baking. To have a glossy crust, the dough must not be over-proofed, and a pasted-type gelation (or steam) must take place before there is any chance of crumb-type gelation with a minimum oven temperature of 74 ℃ (165 ℉).

Baking time varies based on different types of bread, it could be as low as 18 seconds for Arabic bread and over 1 hour for heavy, dense rye breads. Weight loss in the oven could be 9-12% due to bake out. Mass balance in the oven is very important and should be very tightly controlled based on oven loading and optimizing throughput.

Ovens that are widely used in commercial bakery include:

  1. Rotating rack ovens
  2. Tunnel ovens
  3. Single lag tray ovens
  4. Double lap tray ovens
  5. Conveyorized ovens with top entry and bottom discharge
  6. Conveyor ovens with both entry and exit at the bottom
  7. Indirect fire ovens
  8. Direct fire ovens