Why is flour particle size important in cakemaking
White flour that is used in cakemaking is composed mainly of endosperm fragments that have been separated from the surrounding bran during the milling process. The maximum particle size is fixed by the screen sizes in the plansifters in the mill but typically falls around 150 ,um. If we were to examine a straight run white flour we would find some fragments of the original protein matrix (less than 15 ^m), some starch granules freed from the protein matrix (up to 45 ^m), with the remainder being endosperm fragments of varying sizes.
In cakemaking the wheat starch plays a significant role in forming the cake structure as it controls the batter viscosity during heating and helps retain the expanding gases, carbon dioxide (from the baking powder), air (trapped during mixing) and steam (from the added water). This is particularly true for the so-called high ratio flours which may undergo further treatment with heat or chlorine gas in order to enhance their cakemaking properties.
Many of the key processes in cakemaking depend on the surface activity of many materials and so increasing the surface area of the available starch becomes important in aiding stability of the batter. The separation of the starch granules from the protein matrix can be readily achieved by re-grinding and/or air classification. The aim of re-grinding is to free the starch granules from the surrounding protein and lower the maximum particle size of the flour, typically to less than 90 ^m.
Air classification enables fractionation of the flour into components with narrow particle size ranges using air currents. Two or three fractions may be separated using this milling technique. Typically the cut-off points in the air classifiers are set to deliver fractions as follows:
• Less than 15 ^m, comprising fragments of free wedge protein and small starch granules. The protein content will be very high, typically more than 20%.
• Between 15 and 45 ^m, comprising mainly starch granules and smaller fragments of endosperm. The protein content will be low, typically around 8%.
• Greater than 45 ^m, comprising the large fragments of endosperm. The protein content is usually close to that of the base flour, typically around 10%.
Cauvain and Muir (1974) provided a comprehensive study of the effects of changing the particle size of cakeflours and show that treated flours without particle size reduction yielded cakes that collapsed during baking and had a dense cell structure (Fig. 4). Progressive reduction of the maximum particle size decreased the degree of collapse in the cake. They considered that the maximum particle size for cakeflours should be 90 ^m. They also showed that the application of heat treatment or chlorination to the flour could be carried out before or after particle size reduction, which emphasises the importance of flour particle size in cakemaking. Cauvain and Hodge (1977) showed that a
significant proportion of larger particles in cakeflours could also be responsible for collapse in sponge cakes.
Continue reading here: What is heattreated flour and how can it be used
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