Joint International Conference on Long-term Experiments ...

During the chemical changes the pore structure is opened up and becomes continuous. In
this new pore system the water is more free to move. As can be seen from the results, the
measured water content in the centre starts to increase at approximately 70±5 0 C, which
confirms the theory that the water is not free to move until the structural change occurred.
The partial water vapour pressure gradient caused by the temperature gradient attempts to
reduce itself.
Figure 3: Typical diagram of the changes in water content under the top crust of the loaf.
The decrease in water content during the first period in the oven is a measured decrease
only, not an actual decrease. When the temperature has reached 70±5 0 C the water
content increases with approximately 3 g water/100 g bread and then slowly decreases
with approximately 13 g water/100 g bread
The water vapour therefore starts to move towards the centre and towards the surface. As
can be seen in Figure 2 the water content appears to increase in the centre when the
temperature has reached 70±5 0 C, and appears to decrease 1 cm from the bottom surface. At
1 cm under the top crust, Figure 3, the results show an increase in the measured water
content immediately after the temperature has reached 75 0 C. This is probably due to the
transport of water vapour towards the colder parts being prevented by the dough. Only when
the interior has changed to bread can the water move freely. Part of the rise could also be
due to compression of the crumb near the surface, as the crust has started to form and the
interior is still rising. Part of the rise could therefore be a measured rise only and not an
actual rise. Figure 4 shows the cross section of a loaf with a rough division into regions of
increasing and decreasing water content, at the time point when the loaf is removed from the
oven. The water contents of the regions have been estimated as a mean value from the
measured water contents. The water content of the dough was 41.8 g waterr100 g dough.
The crust is set at 0 g water/100 g bread, the region below the top crust, DV10 decreasing
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