TYPES OF FLOUR Sell-rising Flour.—In recent years millers have added the chemical reagents necessary to the evolution of carbon dioxide gas directly to their flour. The proportion of the alkaline body, bicarbonate of soda, is generally T% of the flour. Theoretically, a quantity of the acid body should be used just sufficient to neutralize the bicarbonate of soda; but in practice it is desirable and usual to use slightly more of the acid body. In 1928 the acid substance used, in self-rising flours is generally acid phosphate of lime. In recent years the manufacture of this chemical product has been very greatly improved and it is now excellent as to purity and constitution. When the finished self-rising flour con tains i % of bicarbonate of soda, from i 3% to 21% of this phos phate should be used.
In the making of bread the growth of the yeast and the evolu tion of gas was a relatively long process, ranging from 3 to 20 hours. Modern practice has, however, speeded up the fermenta tion process until the usual period of gas production is not more than four hours. While these processes are proceeding the flour as dough is being gradually rendered capable of easy distension and gas retention. It follows that the constitution and character istics of the flour used must conform to the conditions as to time, temperature and proportion of yeast used : so that there is no fixed standard of excellence in flour which can be always meas ured by any known factor, e.g., the percentage of nitrogenous matter insoluble in water. On the contrary, widely differing char acteristics are required, which the miller, as a specialist, must know and satisfy. So far as self-rising flour is concerned, he knows that the evolution of gas is rapid, and that the flour as dough must be capable of rapid distension and good gas retention. Therefore the wheats used in the manufacture of such flour differ substantially from those used for the manufacture of bread flours; and even in the manuf*ture of the latter regard must be paid to the conditions of time and temperature and to the sort and proportion of yeast used. These considerations have led to many refinements of manufacture and to the most modern devel opments of milling.
In Great Britain the type of bread-stuff consumed has changed to a substantial extent and has been affected by the increase in the number of tea-shops and the growth of the "tea" habit ; that is to say, while the consumption of bread per head of the population has declined, the consumption of cakes, scones and "small goods" has greatly increased. The consumption of flour and wheatmeal per head of the population appears to have been stationary in re cent years in Great Britain, and stands at 227 lb. per head of the population per annum. In the United States until 19oo this was also true, standing at about 224 lb., but then it declined and seems now to be about 176 pounds. In France the figure appears to be much higher than in either Great Britain or America.
Numbers benefit by the presence of bran or "roughage" in their food, and a proportion of whole-wheat bread is widely recommended. During the World War it was ascertained that brown flours formed 5% of the total flours consumed in Great Britain. This group of bread-stuffs comprises certain well-known proprietary flours that are not whole-meal, and it is safe to say that wheatmeals then formed only from 2% to 3% of the total flours consumed. There is no reason to think (1928) that this proportion has been substantially increased either in Great Britain or the United States. Wholemeals remain much discussed.