Purifying and Bleaching

PURIFYING AND BLEACHING Purifying.—In a technical sense purifying connotes separa tions of the granular products known as semolinas and middlings according to compactness of particle. For this purpose the machines known as purifiers have been designed and built. Before sorting by compactness of particle can be performed, sorting by size of particle is necessary, and must be carried out in great detail. There are various forms of this purification. Generally there is a sieve divided into a number of sections, each one having above it a separate air compartment. Through the sieve and each air compartment a current of air, under control as to intensity, is drawn. The best particles pass through the meshes of the sieve, some are held in suspension on the sieve and are floated over its end, others are caught in receptacles placed above the sieve.

Bleaching.

The colouring matter of both flour and carrots is carotin, though there is less of it present in flour than in car rots. As a constituent of flour it seems to serve no useful pur pose, and generally consumers do not like bread which is even moderately yellow. On the other hand, some farmers prefer, for some reason or another, to grow those varieties of wheat which, on milling, yield yellow, sometimes intensely yellow, flour. If such flour be exposed to the atmosphere for a sufficient time it becomes whiter, the oxides of nitrogen which exist in the atmos phere entering into combination with the carotin to remove or diminish its yellowness. In the processes of bleaching flour this is effected by artificial means. A small current of air is pumped through a chamber in which flaming electrical discharges are pro duced intermittently. As a consequence, nitrogen peroxide is produced, and this, mixed with the excess air, is passed into the flour and oxidizes the .colouring matter. Flour thus treated may contain up to four parts per million of residual nitrites. This process has been examined at great length in the law courts and elsewhere and found to be innocuous to the ultimate consumer of bread-stuffs. Bleached flours must however be so labeled if intended for sale in the United States.

Minute proportions of benzoyl peroxide will also bleach flour, and so will traces of nitrogen trichloride. These substances have been very closely investigated and are permitted in several coun tries. A departmental committee appointed by the British Minis try of Health has advised against their use but they have not been prohibited in Great Britain. The development of new processes for the bleaching of flour is still in an active state of investigation. The question of the merits of the natural aging of flour versus bleaching and the use of "chemical substances" as yeast foods or as flour or bread "improvers" or enrichment mediums will prob ably remain a subject of controversy until more is definitely known of the factors which determine flour quality. The physiological side of the problem has not been the subject of extensive investi gation in the light of the new knowledge of nutrition, and this too will probably remain in the field of controversy until scientific opinion is more in accord. (See GRAIN PRODUCTION AND TRADE; SEMOLINA ; MIDDLINGS ; etc.) (A. E. Hu.; H. E. BA.) BIBLIOGRAPHY.--British Association, Reports (19(7, 1909, and 191I) ; Bibliography.--British Association, Reports (19(7, 1909, and 191I) ; T. B. Wood, The Story of a Loaf of Bread (1913) ; P. A. Kozmin, Flour Milling (Trans. from the Russian by M. Falkner and T. Fjelstrup, 1917) ; Royal Society, Reports of the Grain Pests (War) Committee (Liverpool, 192o) ; W. C. and W. Jago, The Technology of Bread-making (192 1) ; P. A. Amos, Processes of Flour-Manufacture (new ed. rev. by J. Grant, 1925) ; C. H. Bailey, The Chemistry of Wheat Flour (Amer. Chemical Soc. Monograph Series, 1925) ; D. W. K Jones, Modern Cereal Chemistry (rev. ed. Liverpool, 1927) ; Report of the Departmental Committee of the Ministry of Health on the Treatment of Flour with Chemical Substances (H.M. Stationery Office, 1927) . See also, National Joint Industrial Council for the Flour Milling Industry, Technical Education Series; and Incorporated National Assoc. of British and Irish Millers, Reports of the Home Grown Wheat Committee. (A. E. Hu.)