Miller Magazine Issue: 119 November 2019

76 ARTICLE MILLER / NOVEMBER 2019 of the subsequent milling process will be affected in a bad way. So that the break system in flour milling is the most critical operation. This is where the miller has to use his skill and knowledge to minimize flour production as much as possible in the break system with that the amount and purity of white final flour that he can produce measure the skill of the miller (Bunn, 2000; Campbell, 2007). Breakage of wheat kernels during first break roll- er milling depends on the characteristics of the wheat (including the distributions of kernel size, hardness and moisture content) and on the design and operation of the roller mill (including roll speeds and differential, roll disposition, fluting profile, number of flutes, fluting spiral, roll gap, the degree of roll wear and the feed rate). The effects of these factors are manifest in the particle size distribution exiting first break, the compositional distribu- tion of those particles (as large particles tend to be richer in bran, while small particles are pure endosperm), the power required to mill the wheat and the rate of roll wear. (Campbell, 2007) WHAT ARE BREAK RELEASES? The break release percentage is the amount of ground material obtained, consisting mostly of sizing, middlings, flour, and fine bran, reported as a percentage of the orig- inal material being tested through a certain sieve aper- ture. A schematic of a break release test is presented in Figure I. The following equation should be used to calculate break releases: in which W1 = weight of sample, and W2 = weight of overs on the sieve after sifting. The break release val- ues are actually the percentages of the stock passing through the sieve. WHY ARE BREAK RELEASES NECESSARY? Before contacting the break releases necessary, mill balance term should be explained. Mill balance is defined in “Dictionary of Milling Terms” as “the proper distribution of stock to the various parts of the milling system, as de- termined by the flow sheet, to ensure proper loading of equipment and high milling efficiencies” (Gwirtz, 2002). In order to achieve op timum efficiencies of all machines within a mill, all sections of the mill should be fully utilized and the miller ensures t he correct amount of stock from the break rolls to the su bsequent roller mills/sifters/puri- fiers is entering as it wa s designed to receive to keep it in balance. The amount of stock is as important as the type of stock - quality and particle size. If these quantities are changed for any reason then some areas of the mill will be underloaded and other areas will be overloaded, thereby causing an imbalance in the milling system. This imbalance will result in poor milling efficiencies, further resulting in poor extraction, poor flour quality, higher mill- ing costs and lower mill capacity (Bunn, 2000; Posner and Hibbs, 2005). An imbalance in the mill flow to plansifter causes bare or over dressing that results bad flour quality. When a sifter is receiving too much product then there will be a higher percentage of fines over tailing which will auto- matically overload the passages further down the sys- tem. If a sifter is not receiving enough product then the percentage of over tails will be low, which will result in more lower quality fines passing through the sieve also causing all following machines to have less quantity of product than they were designed to have therefore caus- ing bare dressing to be accentuated right down the flow (Bunn, 2000). Break releases are used to (Bunn, 2000; Posner and Hibbs, 2005). Fig. 1 Schematic explanation of break release