Grain handling and processing in China, Europe, Japan, the United States, and other parts of the world have taken different directions, as individuals came up with novel ideas. Modern communication allows us to learn about these developments, which were achieved in isolation. In Avartin Company, we tried to bring together many ideas and new innovative approaches to theory and practice in wheat flour milling.
Wheat moisture is not a grade factor, but some countries indicate a maximum allowed moisture content in wheat (France, 16% and Australia, 12.5%). In Canada, five levels of moisture content can be applied to grades: straight, tough, damp, moist, and wet. Red spring wheat, for example, is straight grade if its moisture content is 14.5% or lower; tough if its moisture content is between 14.6% and 17.0%; and damp if its moisture content is over 17% (CIGI, 1982). Proximate data such as protein content are corrected in the United States to 12% moisture basis and in European countries to dry basis. The logic behind the usage of 12% as the moisture basis for wheat is that, in general, at about 25°C and 60% relative humidity, wheat moisture will equalize to 12%. Under the same conditions, flour moisture would equalize to about 14%. Accordingly, wheat farmers, traders, inspectors, and millers recognize wheat moisture determination as one of the major parameters. In the United States, the Motomco 919 moisture meter is the approved instrument used by GIPSA (Fig. 1-4). Various testing methods for wheat moisture exist, of which the most popular are based on the following principles; drying, distillation, chemical, electrical resistance, electrical capacity, microwave, and infrared absorption.
Ash is the residual inorganic material left after incineration and is expressed as a percentage of the original sample. The ash value is corrected to a dry basis or any moisture basis for comparison. Ash is another quality factor used to evaluate wheat flours and other mill products in the trade. Millers are always looking for wheats that will produce low-ash flours, but there are unusual instances that affect this objective. Certain wheats produce relatively low-ash straight grade flour, but, regardless of the amount of clear flour that is taken out, it is difficult to produce a low-ash patent flour. Other high-ash, straight-grade flours lose ash rapidly as clears are removed. These examples show that inorganic material is not always produced in the same way in the bran and endosperm of different samples of grain.
The gradient of ash content increases from the center to the outer layers of the wheat kernel . This variability of mineral content can be attributed to environmental and genetic factors and to their interaction. Several mineral elements show high positive correlation with protein content in both flours and bran. In some varieties, ash is concentrated in the outer layers of the endosperm. In this case, the ratio between straight-flour ash content (FA) and whole-wheat ash content (WA) is lower. When this value is known, the efficiency of the mill can also be determined by comparing the actual FA/WA to the optimum FA/WA. Small variations of ash in flour do not necessarily imply the presence of different amounts of bran. In general, the ash itself does not affect flour properties, and thus it can be argued that ash content should not be regarded as a flour quality parameter in bakers’ specifications. However, as is shown later, ash values of wheat, intermediate streams in the mill, and final products can be important means and tools for mill adjustment and control.