Technology of Baked Goods - Sourdough Biotechnology - page 69

sugars in the Maillard reaction, forming a number of compounds responsible for the
colour and typical aroma of the crust [ 53 ]. If the intensity of the Maillard reaction
does not exceed certain limits, these effects contribute to the sensory properties. On
the contrary, the protein-sugar interactions lead to unavailable lysine and, in
advanced stages, cause the synthesis of toxic compounds. The International Maillard
Reaction Society site ( http://imars.case.edu ) provides more information on the
nutritional and sensory properties of baked goods.
The intensity of the colour of the crust is strictly related to baking temperature,
while the thickness of the crust is influenced by baking time. Baked goods undergo
a loss of weight during baking, a key step of the process. Usually, bakers aim to
obtain the highest yield according to the values of humidity which are allowed by
national regulations. In that sense, the practice of including vapour in the oven dur-
ing the initial baking is justified. The vapour condenses on the surface of the dough,
accelerates heat transfer to the dough, slows down evaporation, and decreases
weight loss [ 45 ]. As a further positive effect, the viscoelastic properties are retained
for a longer time on the surface of the dough, allowing a higher development of the
baked goods.
In the oven, the heat transfer towards the dough occurs by radiation from the
walls and by air convection. Inside the dough, the transfer occurs by conduction.
Because the temperature is usually between 200 and 230°C, the kinetic of baking is
quite slow and provides the consolidation of the internal structure without unaccept-
able scorching of the crust.
Ovens
Regardless of the characteristics of the oven, the baking floor is called the sole or
deck and the upper part of the chamber the crown.
Ancient ovens, often made of stone or bricks, had a single chamber where com-
bustion and baking occurred. This type of baking is referred to as a “direct firing
system” because the combustion gases are in contact with the dough. The initial
temperature reaches 350-400°C and decreases during baking to 160-170°C. These
ovens, today used only for special traditional or typical breads (e.g. Italian Altamura
bread or Arabic bread), were replaced by ovens with an “indirect firing system”,
where the combustion area is separated from the baking chamber and the combus-
tion gases do not come in contact with the dough but circulate in tubes above and
below the baking surface [ 47 ]. This configuration provides a higher uniformity of
heating and guarantees hygiene. The heat transfer may be improved using forced air
systems inside the chamber (ventilated ovens) or forcing the circulation of the com-
bustion fumes into tubes via a ventilator (Cyclotherm ovens). This method also
improves the heat exchange thanks to the repeated passage of the combustion fumes
within the tubes positioned above and below the conveyor. Heat is transferred to the