Technology of Baked Goods - Sourdough Biotechnology - page 67

physical stresses associated with compression, followed by cutting and shearing.
The working of the divider is completed by rounding and moulding the individual
pieces with different machines. Generally, three steps are carried out: the sheeting
of dough pieces into a uniform layer, the rolling into a cylinder by means of a round-
ing or curling machine, and compression to obtain the desired shape.

3.4.3.4 Baking

Baking is considered the most important stage of the entire cycle. During baking,
the dough heats up and loses humidity. Heating occurs from the outside towards the
inside, water loss occurs in the opposite direction. These two phenomena cause
multiple changes, differing in their physical, chemical and biochemical nature and
intensity, according to the temperature and the area of the dough. The change from
the foam state to the sponge state [ 52 ], and the diversification between crust and
crumb are observed.
The sequence of changes (Table 3.5 ) is different according to bread area. The
temperature inside the dough is always below 100°C, while on the surface it reaches
180-200°C. As soon as the leavened dough is inserted into the oven, the fermentative
activity increases [ 38 ] until microbial death occurs at temperatures higher than
50°C. Heating causes a further significant volume expansion (oven spring) of about
40% of the volume compared to the leavened dough, corresponding to an increase
of the surface area of 10% [ 49 ]. The volume occupied by gases, CO 2 , ethanol
vapours, water vapour, increases as the temperature increases. Starting from 70°C,
the chemical and biochemical transformations of the macromolecules stabilize the
complex. A porous network of interconnected alveoli separated from each other by
a solid matrix with very fine walls is formed [ 52 ]. During this passage, proteins and
starch achieve new properties. The gluten is denatured, completely loses its extensi-
bility and achieves elasticity. The starch swells up and gelatinizes. The intensity of
these two phenomena depends on the distance from the geometric centre of the
dough. Baking is completed when, even in the most internal part of the dough, the
temperature has reached values that promoted the structural consolidation. The tem-
perature at the centre point has to be in the range of 90-95°C to prevent collapse due
to a non-rigid structure [ 52 ] .
Because of the temperature gradient that is created in the dough during baking, the
surface, which is exposed to the oven temperature from the beginning, reaches the
sponge state much more quickly than the internal part. The surface areas, therefore,
become more and more dehydrated and permeable, facilitating evaporation and the
release of the water vapour that is generated and accumulated within. Once baking is
completed, the crust has a humidity of less than 5% [ 2 ] . This value ensures friability
and crispiness. The internal crumb retains higher humidity and remains soft and light.
The complex chemical reactions that occur during baking are of marked impor-
tance for the aroma and taste of baked goods. The starch in the crust is degraded into
dextrins between 110 and 140°C. Caramelization starts at 140-150°C and contin-
ues, producing pyrodextrins, at higher temperatures. Proteins irreversibly react with