Chemical Properties of Wheaten Flour. 49 



Diastatic Enzyme. 



Obviously, there must not only be a plentiful supply of gas 

 available to distend the loaf, but also to maintain it fully dis- 

 tended until it is fixed in the open. Flours which have relatively 

 little diastatic enzyme will produce insufficient gas. A deficiency 

 of diastase has been actually proved to occur in many flours 

 tested, or, at all events, better loaves have been 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 in- 

 volved in the conception of strength. 



Wood has made comparative determinations of the amount of 

 gas available 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 experi- 

 ments 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 ( f 

 the starch of flour from the point of view of strength. Presum- 

 ably, 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 preponder- 

 ate in amount are from 3 to 5 ju, in diameter, the largest granules 

 are about 30 to 35 /x, and there are also granules of intermediate 



