782 DISCUSSION ON WHEAT: 
obtained in such cases when malt extract or its equivalent has been added 
to the flour; generally flours contain an excess of diastatic enzyme. Gas 
escapes from the dough throughout the process of making a loaf; the 
amount escaping is apparently largest from those flours which contain 
gluten of lowest quality. The power of the dough to retain gas may be 
regarded as one of the separate factors involved in the conception of 
strength, 
Wood has made comparative determinations of the amount of gas avail- 
able for the distention of the dough by incubating flour with yeast and water 
and measuring the gas evolved, special attention being paid to the last 
stages of fermentation, since it is this gas which inflates the loaf at the 
moment it enters the oven. The attempt was made to correlate this factor 
with strength but this view has not been adopted, as it is not in agreement 
with practice. A further objection to these experiments is that they were 
made under conditions very different from those which prevail in actual 
bakehouse practice. 
Another suggestion has been to correlate strength with the diastatic 
power of flour. This is impossible, firstly, because normal flours have more 
than enough diastase to produce the necessary sugar, and secondly, because 
the diastatic power of flour varies materially on keeping the flour sometimes 
increasing, at other times falling. The change in the diastatic power 
affords an explanation of the behaviour of some abnormal flours the baking 
strength of which very materially increased on keeping. Further, the 
diastatic power of flour increases considerably when sodium chloride or other 
salts are added to the dough. 
Starch. 
Hardly any attention has so far been paid to the properties of the 
starch of flour from the point of view of strength. Presumably, however, 
if the starch in one flour is more resistant to attack by diastase than that 
in another flour, sugar will not be formed so easily in the former and gas 
will not be generated so rapidly during fermentation. 
Microscopic examination shows flour to consist of starch granules of three 
different sizes. The smallest granules which preponderate in amount are 
from 3 to 5 » in diameter, the largest granules are about 30 to 35 » and 
there are also granules of intermediate size. The microscopic examination 
of a large number of flours of different origin has shown that the large 
granules vary in number from 6 to 14 per cent. of the total number of 
granules. In other words, in one flour as much as 30 to 40 per cent. of 
the total weight of starch is in the form of large grains, whilst in another 
only 7 to 10 per cent. is in this condition. 
Before a starch grain can be converted into sugar the cellular envelope 
has first to be destroyed. Obviously, when the envelope of the large granule 
is destroyed a much larger proportion of starch is rendered available than 
when the contents of a small granule are liberated. 
Whymper has recently made a microscopic study of the changes occur- 
ring during the germination of wheat. He finds that the larger and more 
mature granules are the most readily attacked by the enzymes of the 
plantlet. Though there is no general relation between the size of starch 
granules of different origin and the ease with which they are attacked by 
diastase and other agents, it appears that the larger granules of any 
particular starch are affected sooner than the smaller granules. 
The destruction of the cellular envelope of the granule is undoubtedly 
effected by an enzyme (cytase) about which very little is known, Julian 
Baker has suggested that poor flours lack a sufficient quantity of cytase, 
and in confirmation of this view showed that the addition of powdered 
malt, which contains such an enzyme, improves the size of the loaves 
obtained from such flours. 
