The "Pyler says" series explores excerpts from Baking Science & Technology, a textbook that teaches readers a range of baking and equipment concepts. The following passage is from Chapter 6: Fundamental Bakery Dough Processes —Heat Transfer.

In conventional baking processes, heat is transmitted to the dough piece in three different ways, namely, by radiation, convection and conduction (Matz 1972). While all three modes play significant roles in baking, their relative importance depends largely on the type and design of the oven. Condensation and evaporation, which involve latent heat, also are involved.

Radiant heat consists principally of invisible infrared rays that emanate from the heated internal surfaces of the oven. Its behavior differs from the other types of heat in two distinct ways: it is blocked in its transmission by any intervening opaque object, and it is highly responsive to the absorptive properties of the product that is exposed to it.

Convected heat is that which is transferred by means of inter-mixing fluid media such as air, water, vapor or combination gases. In ovens, convected heat is distributed through the baking chamber by the turbulence of the internal atmosphere and is transferred by conduction to the dough piece when the hot air contacts the dough surface. The hot air enters the oven chamber through perforated pipes or plates, called “coloraiders,” located above and below the product. It is recommended that the air is blown onto the product in a defined pattern to provide good color development and maximum heat transfer.

Conducted heat is that which is transmitted by physical contact from one body to another or from one part to another in the same body. Thus, the side and bottom crusts in pan bread result mainly from the heat that is transmitted by the walls of the pan, and the gradual heating of the interior of the dough piece during baking is also largely the result of heat conditions.

According to Matz (1972), conduction and radiation tend to localize heat differentials, with conduction acting to raise the temperature of the loaf bottoms and sidewalls of pan bread, and radiation that of exposed loaf surfaces; convection, on the other hand, tends to create a more uniform heat distribution within the oven.

Sluimer (2005), however, stated that conduction contributes only a small part of the heat transport of baking, and the greater part of the heat required to bake a product originates from condensation of steam within the product. Bakery engineers and bakers alike (Sievers 1978, Lanham 1994) have observed that the cellular structure of dough makes it a poor conductor of heat.  

Matz, S.A. 1971. Bakery Technology and Engineering. 2^nd ed. Avi Publishing Co.: Westport, CN.

Sluimer, P. 2005. Principles of Breadmaking: Functionality of Raw Materials and Process Steps. AACC International: St. Paul, MN.

Sievers, R.S. 1978. New Baking Methods. Proc. Am. Soc. Bakery Engrs. 54: 98.

Lanham, W.E., Jr. 1994. Efficient Oven Usage. Proc. Am. Soc. Bakery Engrs. 70: 141.