Cereals processing technology

Breadmaking 219
application of a mixture of 60% oxygen and 40% nitrogen based on the
principles of providing improved ascorbic acid oxidation (Chamberlain, 1979).
The most common applications of CBP-compatible mixers are the high
capacity production of fermented products in plant bakeries running continuously.
Mixing plants are available with outputs from 2,000 to 10,000 kg
dough per hour. More bread is produced from dough mixed with CBPcompatible
mixers in the UK, Australia, New Zealand and South Africa than
from any other mixing system. The use of CBP can also be found in India,
Germany, Spain, Ecuador and the USA.
Horizontal bar mixers
Horizontal bar mixers are usually capable of mixing large quantities of dough in
one batch. In the USA 1,000 lbs of dough at a time is a common size. This large
size provides the necessary quantity of dough for very fast production rates.
Mixing speeds are commonly lower than those used with CBP-compatible types,
typically the maximum speed will be less than 150 rpm. The horizontal mixer is
most often used with the sponge and dough process (Stear, 1990).
The mixing action of the horizontal bar mixer depends on the design of the
beater arms in the chamber. The two main variations are based on roller bars and
elliptical-shaped beaters. In both cases the mixing action is strongly influenced
by the relatively small size of the gap between the outer edge of the beaters and
the sides of the bowl. The main action tends to be one of stretching and folding
of the dough. The dough is picked up by the mixer blades and thrown against the
outer side of the bowl but because of the slower speed less energy is transferred
to the dough than with CBP-compatible types. Gravity also plays a role in that
the bulk of the dough will fall to the base of the mixer where it is partly picked
up for further mixing and partly stretched as the mixing tool moves through the
dough.
The lower mixing speed means that a longer mixing time is required in order
to develop the gluten structure of the stronger flours which tend to be used with
sponge and dough processes. The slightly longer mixing time also allows for
longer contact times with the mixing bowl and so cooling jackets can therefore
be more effective at removing the heat generated from dough mixing.
10.8.3 Cell creation during mixing
The production of a defined cellular structure in the baked bread depends
entirely on the creation of gas bubbles in the dough during mixing and their
retention during subsequent processing. After mixing has been completed the
only ‘new’ gas which becomes available is the carbon dioxide gas generated by
the yeast fermentation. Carbon dioxide gas has high solubility relative to other
gases and in bread dough cannot form gas bubbles (Baker and Mize, 1941). As
the yeast produces carbon dioxide gas the latter goes into solution in the aqueous
phase within the dough until saturation is achieved. Thereafter continued
fermentation causes dough expansion as the gas is retained within the dough