Wheat Flour Milling, Second Edition
Pages 1-46
DOI: https://doi.org/10.1094/1891127403.001
ISBN: 1-891127-40-3
Abstract
The flour miller is the first wheat user who is affected by the quality of wheat. It is estimated that 25% of the flour quality is determined by the milling technology, mill adjustment, and environmental conditions in the mill, and 75% by the quality of the wheat. The miller evaluates incoming raw material for its price and quality. Price is dependent on factors such as supply, demand, and transportation costs. In the trade, quality is mainly based on wheat grading and factors such as protein level and any damage to the wheat. Following the wheat purchase, the miller has the power to evaluate, select, segregate, prepare, and blend wheat mixes for milling. The miller has two ultimate aims: first, to supply the customer with the specified product quality and, second, to efficiently separate the three main parts of the wheat kernel (bran, germ, and endosperm), the economic values of which are related to their purity.
One of the major contributors to variance in quality is wheat variety. Wheat is cultivated on all continents except Antarctica, and about 30,000 wheat varieties of 14 species are grown throughout the world. However, only about 1,000 varieties are of commercial significance. Breads and other products made from flour reflect the characteristics typical of the wheat grown in various parts of the world. Emigration, changes in demographics, changing living styles, and, in many cases, supplying wheat-deficient areas are the main reasons for the transport of wheat from one side of the globe to the other.
Wheat is harvested globally in unbroken continuity throughout the year. Table 1-1 shows the approximate harvest months for some of the major wheat-producing areas.
More than 500 wheat varieties are available in the United States, where a wheat breeder can certify a new wheat variety and sell it on the market. Wheat classification presently is based on a system established in 1916 (U.S. Congress, 1916) and put into effect in 1917. Descriptors such as brush size, germ angle, cheek angle, kernel shape, seed coat texture, kernel color, and kernel vitreousness are used for classification. However, none of these characteristics is directly related to milling and baking quality. This has led to criticism, and currently the wheat-classification system in the United States is under revision.
In some countries, the number of wheat varieties on the market is fixed. For instance, in Canada, the Wheat Board certifies the varieties that farmers can grow. The different varieties grown by farmers are brought together from large areas and blended by local elevators before the bulk of the wheat reaches the mill elevator for storage. The miller evaluates the incoming wheat and segregates it to different storage bins. However, the wheat handling system now also provides identity-preserved (IP) wheat, i.e., wheat that is segregated during growing and harvesting, kept in separate bins, and transported separately from harvest to milling because of specific qualities or milling objectives. The extra efforts required to segregate IP wheat usually result in a premium market price.
Universally, a wheat buyer's first concerns are the cost and sanitation of the raw material. In addition, the buyer must consider the following end-use quality factors: moisture level, percent flour extraction, test weight (TW), kernel size, presence of impurities, percent of damaged kernels, protein content, mycotoxin level, pesticide residue, and end-product functionality. Not all of these factors are considered in the various wheat-classification systems used for trading throughout the world. While wheat milling technology is becoming similar in different parts of the world as a result of knowledge transfer, grading and evaluation of raw material is still inadequate. The lack of an internationally acceptable grading system causes lack of uniformity in shipments, confusion between suppliers, and dissatisfaction among customers. Uniformity among shipments will become more important as processing technologies become more sophisticated and additional quality factors are considered in wheat grading.
In wheat-growing countries, the miller's selection of wheat depends upon the market and upon the location of the mill relative to the wheat supply. A mill located in a soft wheat-growing region usually processes soft wheat. However, Tembo et al (1999) used a decision-making model that confirmed the traditional conclusion that mills should be located near flour users rather than in wheat-production areas. Wheat-importing countries tend to have mills that process many different classes of wheat. Milling several classes requires a more sophisticated milling operation to efficiently process the wheat.
