kept dry, or the enzymes will start to react with the starch in the flour during storage using water
vapour from the air, degrading the starch. The amylases work fastest at warmer temperatures, which
is why warm water is usually added to the original dough rather than cold.
The addition of salt promotes the activity of the flour enzymes the amylases but decreases activity of
the proteases present in flour – which would otherwise hydrolyse the flour proteins and produce a
V/II - 2 (of 3)
After adequate kneading, the dough is placed in a bowl, which is covered and left for several hours
(this is called fermentation). This allows the dough to swell as the yeast respires, producing the gas
CO2. The bubbles do not escape but remain stably incorporated in the dough. The air bubbles are
trapped in the strong protein network.
The yeast is not only responsible for the production of gas bubbles during this time, but also the
flavours and smells that accompany yeast respiration.
During the fermentation, the yeasts use its own enzymes, the maltases, to degrade the maltose
produced by the flours amylases into glucose molecules. It is these glucose molecules directly that are
then converted into carbon dioxide (which helps the bread rise), ethanol (which gives bread its taste),
and diverse aldehydes, ketones, diacetyl, and other alcohols (which help contribute to the breads
C6H12O6----------------> 2 CO2 (g) + 2 C2H5 OH
This is also how the alcohol in beer and other alcoholic drinks as produced.
Fermentation is most effective at temperatures of 27 °C. Although higher temperatures will make the
yeast grow faster and produce more gas, which would increase dough volume, the flavour produced is
best at this lower temperature.
Second kneading step
After fermentation, there is a second kneading step. This step is not so much to strengthen the gluten,
but the constant folding over of the dough during kneading allows the incorporation of air into the
mixture, and ensures that it is distributed evenly.