2009_Book_FoodChemistry

726 15 Cereals and Cereal Products
Fig. 15.41. Fermentation process for biologically leavened dough; temperature 26–32 ◦ C (according to
Bueskens, 1978)
15.4.2.4 Fermentation
Dough passes through several stages of fermentation
in the presence of growing yeast, a biological
leavening agent (Fig. 15.41). After initial fermentation,
the dough is divided and scaled, then the
dough pieces are rounded-off. A short fermentation
is followed by sheeting and moulded dough
fermentation. The dough acquires its enlarged final
volume in the oven. The yeast produces CO 2
and ethanol which, as long as they do not dissolve
in the aqueous phase of the dough, expand
the air bubbles (10 2 –10 5 /mm 3 ) that arise in the
dough during kneading. The volume of a square
white loaf increases 4 to 5 fold and more during
initial, intermediate, and moulded dough fermentation
and 5 to 7 fold during oven fermentation.
The length of time of the fermentation varies. It
depends on flour type (cf. Fig. 15.42), seasonings
incorporated, the amount of yeast and oven temperature.
The flour character determines the fermentation
tolerance, i. e. the minimum or maximum
time after which the fermentation has to
be stopped and the dough loaded into the oven.
Dough fermentation of a weak gluten flour is
rapid, but its fermentation tolerance is low.
Fig. 15.42. The effect of fermentation time on baking
results. (rye-mix bread with two flours which differ in
baking quality; according to Bueskens, 1978)
The main dough fermentation step (cf. Fig. 15.41)
can be substantially shortened by kneading the
dough energetically and/or by incorporating fastacting
additives (for example, a mixture of bromates,
ascorbic acid and cysteine) into the dough.
This provides a favorable dough structure, able
to accommodate large amounts of yeast. This is
the basis for “no-time” dough making procedures,
which provide a continuous flow of dough.
In continuously operated baking processes, the
resting times required during the working of
dough (intermediate and final fermentation) are
realized in air conditioned fermentation rooms.
The resting dough forms pass through these
rooms with a defined speed.
15.4.2.5 Events Involved in Dough Making
and Dough Strengthening
15.4.2.5.1 Dough Making
Bread dough is prepared by mixing water and
flour (70:30 w/w). Water uptake, which depends
on flour type, predetermines most of the subsequent
reactions. A high water uptake favors the
mobility of all the constituents involved in reactions,
e. g., enzymatic degradation of starch into
reducing sugars (Fig. 15.43).
Observation of wheat dough development by light
or scanning electron microscopy reveals that a sequence
of forceful changes occurs in the arrangement
of the water-insoluble flour proteins.
When a light microscope is used to look at
a wheat flour particle under water, practically no
protein structure is discernible (Fig. 15.44, 1a). If
the particle is stretched in one direction by moving
the slide cover glass against the microscope
slide, numerous protein strands with inserted
starch granules become visible. These strands are