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Milling Characteristics of Wheat

14 December 20175 min reading

“Flour quality characteristics are affected not merely by wheat suitability for specific final product, but also by the type of processing equipment and the suitability of this kind of wheat for milling process all classified as indirect factors.”

Farhan Alfin

Professor Farhan Alfin - Avrasya University

High quality flour cannot be produced from low quality wheat, or from high quality wheat in a failed manufacture. Wheat quality characteristics change according to the user (farmer, miller, and end-user). The millers need to control on both raw materials and manufacture in order to produce a good flour baking quality, and continuous uniformity. The wheat flour quality is determined by its suitability for a specific final product. Flour quality characteristics are affected not merely by wheat suitability for specific final product, which can be determined by some wheat quality characteristics classified as direct factors, but by the type of processing equipment and the suitability of this kind of wheat for milling process all classified as indirect factors.

1. MOISTURE CONTENT Wheat moisture content affects the quantity, price discounts, and storability so that moisture content may affect economic return. Changing the moisture content of wheat will affect its weight and the quantity of dry matter in terms of a hectoliter of wheat which will change the test weight of wheat. Amounts of chemical components in wheat are not affected by the moisture content. However, a percentage of the chemical components are affected by the amount of water in the sample. This is why the percentages of wheat chemical composition are adjusted at 12 percent moisture content. The standard moisture content eliminates the confusion of that results. Thus, the difference between wheat and flour moisture content is important to maximize economic return.

2. DOCKAGE AND FOREIGN MATERIALS Definitions of dockage and foreign materials differ according to the grading system. Dockage is measured by a Carter-Day Dockage Tester. Dockage refers to all materials that can be easily removed with screening procedures. On the other hand, foreign material is non-wheat material that is unlikely to be removed during flour mill wheat cleaning processes.

Whatever the used definition or the procedure in the mill laboratory, every wheat mill has to calibrate its own laboratory results of dockage and foreign materials with the separated materials in the cleaning processes.

3. TEST WEIGHT Test weight is the weight of a measured volume of wheat expressed in kilograms per hectoliter. Test weight is a critical contractual parameter listed in all export sales contracts. Test weight is a general indicator of wheat quality and higher test weight normally means both higher quality grain and flour extraction rate. Test weights decrease as grain deteriorates. Canada and USA determine test weight according to a “clean basis” unlike the process in Australia which is based on “as is/farmer dressed”. Grain moisture and test weight are related to each other in a way that when moisture increases, test weight decreases. To better enhance a good relationship between test weight and flour extraction rate, the test weight should be determined on a “clean basis” and then adjusted to a specific moisture content.

4. 1000 KERNEL WEIGHT (TKW) The 1000-kernel weight (TKW) can be determined from the average weight of 300 individual kernel replicated using the Perten Single Kernel Characterization System (SKCS 4100). The instrument weighs each seed to the nearest 0.01 mg and automatically calculates the TKW based on the average weight of the 300 individual seeds. The average TKW is reported in grams. The 1000 kernel weight is used as an indicator of wheat milling quality which is considered better than test weight. In order to enhance the correlation between TKW and milling extraction rate, TKW can be adjusted to a specific moisture.

5. KERNEL VOLUME AND SIZE DISTRIBUTION The main kernel volume and size distribution can be determined by passing through a stack of sieves or by using the Perten Single Kernel Characterization System (SKCS 4100). The latter measures the average kernel diameter and sample uniformity. The flour yield can be correlated with the percentage of the remaining over each sieve. In gener al, bigger kernels size give higher flour extraction rate and lower ash content. If the percentage of the kernels remained over one of the sieves was more than 75%, or the size distribution of SKCS 4100 had a lower standard deviation, then the sample is uniform. The kernel size distribution is very important during tempering and the flour mill operation.

6. HARDNESS Wheat hardness is the most important quality characteristic that affects tempering, milling operation, baking, and end-use quality. Grinding, crushing, and abrasion are the basic principles of wheat hardness measuring techniques. The most used methods for wheat hardness measurement are PSI, NIR hardness, SKCS, and pearling index. Wheat hardness affects the percentage of flour damaged starch which is in turn an important characteristic that sequentially affects dough rheological properties and end user product quality.

All of wheat characteristics mentioned previously affect mainly the produced flour extraction rate and some flour quality characteristics with combination of milling process operation. Some of them are listed in the seal contract like moisture content, test weight, dockage, and foreign material. However, these characteristics have to be tested again at the mill laboratory following the mill procedures. The others should be determined to predict the flour yield and to help the milling staff control milling process.

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