Food Biochemistry and Food Processing

27 Bakery and Cereal Products 623

pyrroline (roasty), methyl propanal and 2- and 3-
methylbutanal (malty), and 1-octene-3-ol and (E)-2-
nonenal (fatty). An increase in fermentation time
allows for a development of flavor, but this trend is
not really noticeable until much longer fermentation
times are used, as in sourdough breads. There is not
a clear borderline between regular bread and sour-
dough bread.
The production of ethanol and CO 2 is essential for
the development of the desired bread crumb struc-
ture, and several factors affect both the development
of the dough and its leavening (Fig. 27.4). During
fermentation, some of the CO 2 is lost to the atmos-
phere, but most either collects in the small pockets
of air incorporated during dough mixing or is dis-
solved in the dough’s aqueous phase. The amount
that can be dissolved in the aqueous phase is de-
pendent on temperature, and is greater at lower tem-
peratures. As the aqueous phase is already saturated
with CO 2 , it cannot escape from the bubbles by dif-
fusion into the dough, so the bread begins to in-
crease in volume. As the gas collects, the rheological
properties of the dough allow it to expand in order to
equalize the pressure that builds up. Ethanol reacts

with the gluten to slightly soften it, allowing for eas-

ier expansion of the dough. It is important that CO 2

develop immediately after dough preparation and

proceed at an adequate intensity. In addition, the

dough must have the physical properties necessary

to withstand dough manipulation and allow for gas

retention, so that the optimal structure has been

obtained for the final proof and baking (Stear 1990).

THEBREAD-BAKINGPROCESS

When the bread has undergone the final proofing

and is put in the oven, the outer surface rapidly starts

to form the crust. A temperature gradient develops

due to transfer of heat from the pan to the loaf, and if

the loaf is to achieve optimal properties, then the

heat of the oven and the state of the bread proof need

to be synchronized (Stear 1990). Apart from the out-

er crust, no part of the bread ever becomes dry;

therefore, despite oven temperatures of well over

200°C, the temperature in most of the loaf will not

exceed 100°C. The primary rise in temperature

increases the activity of the yeast, and its production

of CO 2. At the same time, the solubility of CO 2

Figure 27.4.Important factors for bread leavening.