Wheat breakage during roller milling

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    Authors & editors

    Bunn, P J [Author]

    Publisher EThOS
    Year of publication 2001 ID: 617000

    Medium Internet source
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    Cereal processes > Flour milling

    Scope & contentThesis submitted to the University of Manchester

    Wheat is the most popularly grown cereal in the world. Over 400 million tonnes of wheat is milled to flour annually for inclusion in baked products. Flour milling has evolved into an efficient operation; however, process modelling, simulation and optimisation can make significant improvements to the operation.

    One such improvement is the use of more informative quality testing procedures to supply information about milling potential of a sample. Breakage matrices were used to describe the breakage function that relates the inlet and outlet particle size distributions over 151 Break. Successful prediction of the milled stock particle size distribution for the native (unsegregated) wheat sample showed that wheat grains milled independently during roller milling; this was confirmed using high-speed video.

    The milling ratio (roll gap over grain thickness) was identified as the parameter determining breakage and enabled a range of roll gaps and inlet particle sizes to be considered simultaneously. The variation in cumulative undersize, P(x), with milling ratio was described by a quadratic function whose coefficients varied in a quadratic manner with particle size (x). Nine breakage coefficients were used to describe the breakage of a wheat variety over a range of roll gaps and inlet particle thickness. The particle size distribution was predicted using the breakage equation and shown to be linear in the range 250-2000 Ilm for 21 different wheats. The slope of the particle size distribution was related to wheat hardness and varied with milling ratio. This variation was shown to indicate the sensitivity of the variety to changes in the milling ratio.

    Flour millers generally prefer varieties with a high sensitivity to changes in milling ratio. Rank Hovis, sponsors of this project, mill approximately 1.6 million tonnes of wheat per year. The results of this study provide the foundation for savings in milling efficiency (through increased flour extraction), wheat substitution (using lower priced wheat in place of high priced wheat). It is estimated that these measures could save over £1m per annum.
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