Technical Talk: January-February 2013

The main purpose of flour milling is to remove the endosperm from the bran and germ and to reduce the endosperm into flour

The main purpose of flour milling is to remove the endosperm from the bran and germ and to reduce the endosperm into flour

Wheat is a major player in most of the world’s diets. Along with corn, oats, rice, barley and other cereals, it has been a main feature of tables for the last 3,000 to 4,000 years. A member of the grass family of plants, wheat is the largest crop produced for human consumption in the world.

Wheat is classified into three categories: growing season, kernel hardness and bran colour. Winter and spring wheat fall into the growing season category. Winter wheat is planted in the fall and remains dormant in winter. It requires exposure to low temperatures in order to produce seed.

Growth of this type of wheat resumes in the spring and is harvested in early summer. Winter wheat normally produces higher crop yield but contains lower protein. Spring wheat is planted in the spring, is harvested in late summer, and normally produces lower crop yield with higher protein content.

Hardness of the kernel distinguishes soft from hard wheat. Hard wheat normally contains more protein than soft wheat, and the proteins of the two types differ in their functionality. Wheat’s colour and bran layer also serve to characterize the wheat into two types (red and white). Red wheat varies in shades of brown and is darker in colour than white wheat.

The wheat kernel (seed or berry) is made of many layers, but the three major parts are the endosperm (constituting 83 per cent), the bran (14.5 per cent) and the germ (2.5 per cent). Flour milling, a complex process, separates these parts. The main purpose of flour milling is to remove the endosperm from the bran and germ and reduce the endosperm into flour. The reduction of endosperm into flour is a gradual process based on the controlled disintegration of wheat kernels. The separation of the endosperm from the kernel during the milling process to make different kinds of flour use three primary techniques: grinding, sifting and purification. The endosperm contains starch granules in a protein matrix, iron and B vitamins. The wheat bran is also separated into feed streams. It is high in complex carbohydrates contributing to dietary fibre, especially insoluble, and contains protein, vitamins and minerals.

Wheat germ is the embryo or sprouting portion of the kernel. It is the most nutrient-dense part of the wheat, containing healthy oils, high amounts of protein, minerals and vitamins such as B and E. The germ is also separated during the milling process and, in many cases, directed into feed streams. Because of the high amounts of unsaturated lipids in the wheat germ, its shelf life is very short and it will become rancid in a few days due to the action of oxidative enzymes. Stabilization of the wheat germ with moist heat will inactivate these enzymes and will extend its shelf life.

Hard and soft wheat are milled into flour used in different baked goods. Due to its lower protein content (eight to 10 per cent) and other quality characteristics, soft wheat flour is used in cakes and other sweet baked goods. In North America, soft wheat flour destined for the production of cakes is also chlorinated at the mill. The chlorine gas interacts with the protein and starch in the flour to improve their performance. In the European Union and other countries, the use of chlorine in food systems is not permitted. Replacing the chlorine treatment of flour for the industrial production of cakes is difficult. The alternative involves the application of controlled moist heat to the flour followed by drying and grinding to produce acceptable cake flour.

Hard wheat flour contains a higher amount of protein (10 to 14 per cent) and is used to make bread and other yeast-leavened products that require gluten strength. There are differences in the quality of flours milled from spring and winter hard red wheat. Hard red spring wheat flour has stronger proteins and is mainly used for breads, pizzas and bagels. Hard red winter, on the other hand, contains more mellow protein qualities. This wheat is used to mill all-purpose and lower-protein flours used for a variety of products, such as cookies, breadings, soft rolls, pan bread, bread sticks and sauces. The characteristics of flour produced from different wheat are influenced by many factors.

Although performance is partly related to protein quantity, the protein quality is by far the major factor. The performance of the flour is more closely related to gliadin and glutenin, the two proteins that combine during the dough development to form the gluten. For example, the higher the gliadin in wheat flour, the higher the extensibility and the lower the elasticity of the dough formed will be. A higher proportion of glutenin to gliadin in the flour will result in stronger and more elastic dough. The quality of the wheat flour is also dependent on starch and other chemical attributes associated with specific varieties. Quality is also connected to wheat class and more closely related to wheat variety.

Other influencing factors include soil conditions, growing season temperature and moisture and farming practices. For this reason, various government and farmer organizations and private companies conduct a survey of the wheat quality each year to determine procurement practices and gather historical information from the different wheat growing areas. The quality of wheat and flour is measured by a variety of techniques and instruments that determine their physical, chemical and rheological properties. In a future article, I will examine these techniques and their role in the measurement of the various quality attributes.

For more information, or fee-for-service help with food technical and processing issues and needs, please contact Dr. John Michaelides at John Michaelides & Associates at 519-743-956, or at Bioenterprise at 519-821-2960 ext. 226, or by e-mail at j.jmichaelides@gmail.com.