Cereals processing technology

224 Cereals processing technology
elongation of gas bubbles in the direction of sheeting is likely to occur and this
orientation is likely to be retained during subsequent curling. Elongation is most
likely to occur with the larger gas bubbles located nearer to the surface of the
dough during sheeting. It is unlikely that the pressures applied during sheeting
will affect the smaller gas bubbles located in the centre of the dough. Nevertheless
the elongation of gas bubbles does affect final bread quality because
when baked into the bread they tend to be shallower than other surrounding gas
bubbles and since they cast less shadow in the cut bread surface they will make
the product appear whiter. Elongation also contributes to the physical strength of
the breadcrumb during slicing and buttering.
The degree to which a dough may be degassed during the sheeting stages of
final moulding depends on the dough rheology and its interaction with the
equipment type and settings used. Whitworth and Alava (1999) have shown that
the de-gassing of no-time doughs is small but examination of X-ray scans of
CBP doughs shows that it does occur. In the X-ray scans the sheeted dough
surfaces are visible as white lines because the dough is denser at this point and
therefore there is greater X-ray absorbance. A further problem which may be
encountered during dough sheeting is the rupture of gas-stabilising films and the
subsequent coalescence of two gas bubbles to form one of larger size. Such
larger sized bubbles have lower internal pressure and carbon dioxide gas may
preferentially migrate to such bubbles causing them grow even larger. Such
damage to dough bubble in structures is thought to be a major factor in the
formation of large, unwanted holes in breadcrumb (Cauvain and Young, 2000).
10.8.6 Proving and baking
Proving is the name given to the dough resting period, after the moulded pieces
have been put into tins or placed in trays, during which fermentation continues
in a controlled atmosphere, typically 40–45ºC and 85% relative humidity. When
the dough enters the prover, it will be at a temperature of 28 to 30ºC. Bakers’
yeast is at its most active at 35 to 40ºC and so running the prover around 40ºC
minimises the time required for proof. It is important that the skin of the dough
remains flexible so that it does not tear as it expands. Since the dough relative
humidity is around 90–95% a moist atmosphere is required to maintain that skin
flexibility.
During proof the starch from the flour is progressively converted into dextrins
and sugars by enzyme action. Yeast can feed on the sugars to produce carbon
dioxide and alcohol, as described above. The carbon dioxide diffuses into the
gas bubbles in the dough causing them to grow and the dough to expand.
Progressively the size of the gas bubbles increases (Whitworth and Alava,
1999). If the dough is confined by a tin the gas bubbles are elongated in the
direction of movement of the dough, i.e. upwards. The frictional forces between
the dough and the tin (even when greased) slow down the movement of the
edges of the dough and so most of the dough expansion occurs in the middle. Xray
tomography has shown that dough expansion in the pan can be so uneven