66o 



BOTANY OF THE LIVING PLANT 



endosperm, which forms 85 per cent, of the grain, is broken down in 

 the process of milling into fine flour, semolina, and other products. Its 

 analysis shows that, while about three-quarters of it consists of starch, 

 there still remains in it about 10 per cent, of protein, which, as " gluten," 

 forms the basis of the dough of bread when moistened with water. 



The purpose of milling of grain was in the first instance simply to 

 grind it into small parts. The bread of primitive Man was doubtless 

 " wholemeal " bread. But even in the old stone-grinding the products 

 were usually graded roughly as bran, pollard, sharps, middlings, and 

 fine flour. Sometimes the coarser products were reground, and the 

 fine flour again extracted from them ; but mostly they were regarded 

 as " offals," and were fed to stock in various forms. More recently 

 in the process of roller-milling the grain is comminuted more accurately 

 oy successive stages, being passed through rollers with successively 

 finer ridges. The products of these successive ' breaks " are sifted 

 partly by screens, partly by air-blasts, so arranged that their various 

 grading can be very perfectly carried out. The end-product of greatest 

 importance is the flour. The finer this flour is graded the less percentage 

 of it will be yielded from the milled grain, but the whiter will be the flour 

 and the bread made from it. In practice the highest percentage of finest 

 white flour that can be obtained is about 70 per cent, of the weight of 

 the whole grain. Higher extraction results in a flour showing some degree 

 of brownness owing to the inclusion of a proportion of bran. In deciding 

 the type of flour that is to be produced, various aspects have to be con- 

 sidered, such as nutritional value and acceptability, and there has been 

 some difference of opinion on the matter. In war-time the need for 

 economy gives added importance to a relatively high extraction. During 

 the 1939-45 War, British national flour has been based on an extraction 

 of 80-85 per cent, of the wheat grain. 



A comparison of the analyses of average samples of the grains in 

 common use by Man gives a basis for estimating their relative values 

 as foods. The average of a large number of different samples of each 

 is given in the subjoined table : 



TABLE OF ANALYSES OF CEREAL GRAINS. 



