116 
Mr Wood , A New Chemical Test 
In baking bread, flour, water, and yeast are mixed together 
in certain proportions, the mixture being called dough. The 
dough is allowed to stand in a warm place while it undergoes 
the change known as “rising.” This rising is caused by the 
yeast finding sugar in the flour, which it converts into alcohol 
and carbon dioxide gas, the latter of which being held in the 
dough increases its volume. It seemed therefore that the volume 
of the loaf should depend on the expansion of the dough by the 
carbon dioxide formed by the growth of the yeast, and this 
expansion must in turn depend either on the amount of sugar 
at the disposal of the yeast, which would decide the volume of gas 
formed, or, if there were abundance of sugar in all flours, on the 
capacity of the dough to retain a large amount of gas. The first 
of these suppositions was obviously the easier to test, and it has 
been found to give, in all cases tested, a satisfactory explanation 
of the cause of the size of the loaf. 
To test this supposition that the volume of the loaf is due 
to the amount of sugar at the disposal of the yeast, a number 
of flours were obtained from Mr A. E. Humphries, Chairman of 
the Millers’ Association, and of the Home-grown Wheat Committee, 
who has had much experience in measuring the practical baking 
value of flours, and who has helped me continually with material 
and advice throughout the investigation. Small weighed quantities 
of these flours were mixed with yeast and water in bottles 
connected with measuring tubes. The bottles were then incubated 
at a temperature of 35° C., and the volumes of carbon dioxide 
evolved from each recorded at intervals. It was at once noticed 
that all commenced to evolve gas at practically the same rate, 
but that after about an hour some continued to do so at the 
original rate, whilst others gradually slowed down. After about 
24 hours, when all had ceased to give off gas, the total volumes 
were read. In the following table the total volume of gas evolved 
by 20 grams of each flour treated in this way is recorded, side by 
side with the “ strength ” as determined by Mr Humphries in the 
bake-house. Mr Humphries defines strength “as the capacity for 
producing a large well-piled loaf,” and it will be noticed from his 
definition therefore that volume is a large factor in his measure- 
ments. His scale is a purely arbitrary one in which the best 
flour he could obtain gets 100 marks, whilst the mark 0 represents 
a flour which is unbakeable. 
Inspection of the table at once shows that the volume of gas 
given off closely follows the baker’s marks, with two notable 
exceptions in nos. 1 and 8. These two exceptions after enquiry 
gave perhaps the strongest proof of the rule. It was found that 
no. 1 only obtained a mark of 96 when baked after mixing with 
malt extract, a treatment which would undoubtedly increase the 
