57 Predicting roller milling performance from single kernel parameters.

G. M. CAMPBELL (1), P. J. Bunn (1), C. Webb (1), and S. C. W. Hook (2). (1) Satake Centre for Grain Process Engineering, UMIST, P.O. Box 88, Manchester, UK; (2) RHM Technology Ltd., Lord Rank Research Centre, Lincoln Road, High Wycombe, Bucks, UK.

During First Break roller milling of wheat, the output stock characteristics arise as the sum of the breakage of individual grains. These in turn break according to their individual parameters, such as size, shape, hardness, density, mass, moisture and protein content. Knowing how individual particles break, as a function of their individual characteristics, in principle allows prediction of the milling of entire mixtures of grains. This provides a basis for relating single kernel tests to roller milling performance. Wheat breakage depends also on the roller mill operation, of which the major adjustable variables are roll speed, differential and, most importantly, roll gap. Results are presented which show that breakage of wheat grains during roller milling depends on the milling ratio (the ratio of roll gap to input grain size). Different sized wheat grains of the same variety break to give the same output particle size distribution for the same milling ratio. Within a mixture of grains, there is a range of grain sizes and hence milling ratios. A model of wheat breakage as a function of milling ratio is presented. The model is integrated over the range of milling ratios encountered by a sample during milling, to predict the output particle size distribution at different roll gaps for several wheat varieties.