The separation of flour into fractions of different protein contents by means of air classification

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Abstract
Fractions of markedly different protein contents may be obtained by air‐classifying flour (in the sub‐sieve range) at cut sizes of about 17 and 35 μ respectively. Of these fractions, the fine, 1 (of high protein content), contains fragments of interstitial endosperm protein and small starch granules; the intermediate, 2 (low protein), mainly large starch granules; the coarse, 3, fragments of endosperm cells. The yields and protein contents of the fractions vary with different wheats; the yields of 1 and 2 may be greatly increased through suitably grinding the flour after milling.In general, 1 may be used for raising the protein content of flours deficient in protein to a level suitable for bread‐making. The amount of 1 required depends on its protein contents and on whether it came from a hard or soft wheat, the hard wheat fraction having better bread‐making qualities. The resulting variation in the proportion of 1 required in the blend causes variation in the proportion of other particulate materials introduced with 1, in which they have become concentrated during the air classification. These include diastatically active agents and finely divided discolouring matter; the level of the former reached in the blend greatly affects its bread‐making value. Pre‐grinding of the flour may be helpful in this respect.When chlorinated, 2 is potentially useful for making light‐structured cakes, but hard English wheats have mainly given less satisfactory results than soft. Under certain conditions, 3, with or without 2, may be better for biscuit‐making than the parent flour.

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