Food Chemistry

15.4 Baked Products 731

Fig. 15.45.Tensile tests with dough made of flour from
the wheat cultivar Soisson (according toKiefferand
Stein, 1999). Dough after 45 min rest without shear (–
), dough with shear after 135 min (•–•), dough with-
out shear after 135 min (—)

sequent dough resting stage and contracts to form
islands which are only slightly connected to each
other (Fig. 15.46b). In shearing (Fig. 15.46c),
these islands aggregate to form a network made
of thicker gluten strands. The extent of the effect
depends on the variety of wheat. In cultivars with
weak gluten, the gluten is finely distributed even
after shearing and the net is only weakly formed.
The driving force behind the unmixing of starch
and gluten is the tendency of gluten proteins to
aggregate via intermolecular interactions, e. g.,
hydrogen bridges and hydrophobic interactions.
Rye contains fewer gluten proteins than wheat.
In dough development, its aggregation is addi-
tionally hindered by pentosans so that no gluten
network can be formed.
Baking experiments have shown that the dough
stability during fermentation is better, the bak-
ing form rounder and the baking volume larger if
a clear unmixing of starch and gluten occurs due
to the shearing of dough.

15.4.3 Baking Process

15.4.3.1 Conditions

The oven temperature and time of baking for
some baked products are summarized in Ta-
ble 15.50. Conditions for baking of rye and

rye mix bread sometimes deviate from these

values. They are prebaked at higher tempera-

tures, for instance at 400◦C for 1–3 min, and

then post-baked at 150◦C (for the effect on

quality see Table 15.51). In a continuous process,

tunnel-type ovens with circulation heaters are

used. Gratings frequently serve as the conveyor

band.

In an oven with the temperatures given in

Table 15.50, since heat transfer occurs slowly

in dough, there is a steep temperature gradient,

200 → 120 ◦C, inward from the crust of the

dough piece. By the end of baking, a temperature

of 96◦C is attained within the product. Higher

temperatures up to 106◦C are found when the

crust is able to resist the rise in inner steam

pressure. The water evaporates only in the crust

region during dough baking. Water diffusion

towards the center of the bread can give the fresh

crumb a higher moisture content than the dough.

The steam concentration in the oven also affects

the baking results. A steam header is provided in

most oven designs to regulate oven moisture.

A baking weight loss is experienced as a result

of water evaporation during crust formation. The

extent of the loss is related to the form and size of

the baked bread and is 8–14% of the fresh dough

weight.

15.4.3.2 Chemical and Physical Changes –

Formation of Crumb

The foamy texture of dough is changed into the

spongy texture of crumb by baking. The follow-

ing processes are involved in this conversion.

Up to ca. 50◦C, yeast produces CO 2 and ethanol

at a rate that initially increases. At the same

time, water and ethanol evaporate and, together

with the liberated CO 2 , expand the exisiting gas

bubbles, further increasing the volume of the

baked product. Parallel to this, the viscosity of

the dough falls rapidly in the lower temperature

range, reaches a minimum at ca. 60◦C, and

then increases rapidly (Fig. 15.47). The increase

is caused, on the one hand, by the swelling of

starch and the accompanying release of amylose

and, on the other hand, by protein denaturation.

These processes result in a tremendous increase

in the tensile stress of the dough and in the

pressure in the gas bubbles at temperatures