Technical Talk: Wheat flour fundamentals

Humans have been consuming wheat and wheat flour for thousands of
years. Cultivation of the land and the growing of crops were introduced
about 10-15,000 years ago when agricultural implements were first
developed.

What’s new with wheat and other flours and how are these changes affecting the baking industry?

Humans have been consuming wheat and wheat flour for thousands of years. Cultivation of the land and the growing of crops were introduced about 10-15,000 years ago when agricultural implements were first developed. Ever since, humans have been able to grow grains for food instead of gathering them from naturally grown wild grasses.

Because grains and other seeds are naturally dry, they can be stored for long periods of time, transported and traded for other foods. The next step was the processing of these grains into a more palatable state by breaking them down into smaller particles and further mixing them with water and cooking them. The grinding of wheat and other grains into flour or meal began about 8,000 years ago, as evidenced by the state of the teeth of human remains found from that period showing no evidence of markings that would indicate the chewing of whole grains.

The grinding of seeds into flour was a crude process of pounding or rubbing two stones together to produce a meal. This process has evolved over thousands of years to the modern milling practice in which tons of wheat can be milled per hour with automated equipment to produce the many types of flour we know today. Milling technology evolved from human hands to the use of animals, such as horses and oxen, and then water and wind as a source of power to turn grinding stones and produce larger quantities of flour.

In these early years it was desirable to separate the bran and germ from the endosperm in order to produce a more palatable easier to chew flour. The separation was crude and carried out by simple sifting. Although the grinding of wheat into flour has been practised for thousands of years, the real progress in the milling of wheat came with the introduction of rollers to replace grindstones and the steam or electricity to provide the power.

The roller mills provided advantages in higher extraction of flour from wheat and better separation of bran and germ. Today’s modern mills have the ability to produce many types of flours from soft, hard and durum wheat as well as other specialized grains. Because of their ability to separate various streams, modern mills can also produce flour for different applications from the same wheat.

Recent advances in milling include preprocessing of wheat, which is a method of gradual removal of some of the outer layers of the grain prior to milling. This technology results in higher extraction yields and cleaner flour. The application of this technology is particularly valuable for the production of higher quality durum semolina with better performance and colour.

More recent advances in milling come with the development of whole grain flour. In the past, consumers in North America preferred white bread to brown. This demand is ongoing, especially among young consumers.

Today’s consumer, however, is health conscious and is looking for more fibre and the nutrients found in whole grains. Bread and other baked goods made from traditional whole grains that contain germ and bran are dark in colour. Because the preference for light colour is still prevalent, there is demand for whole-grain, light-coloured flour. To satisfy this demand, several companies developed light-coloured, whole-grain flours. Manufacturers are producing these light-coloured, whole-grain flours from specific varieties of wheat and developing new methods of milling flour. These flours have a much finer particle size and as a result the colour appears much lighter. Because of the incorporation of the germ into the whole grain flours and the presence of high amounts of mono- and poly-unsaturated fat, these flours are more prone to oxidation and therefore have a much shorter shelf life. Products made from these flours will also have a shorter shelf life.

Wheat flour as an ingredient in the production of baked goods
The use of flour in baked goods goes back to ancient Egypt, where there are references (wall paintings) of crudely sifted flour being mixed with liquid containing natural yeast and making loaves of yeast-leavened bread.

Wheat flour is a unique ingredient. It contains starch and other carbohydrates (fibre, pentosans, etc.), protein, minerals and lipids. No other flour has the ability to perform the same way and make bread and other yeast-leavened products than wheat flour.

This unique ability is attributed to wheat flour’s specific protein content. When hydrated and mixed, the proteins in the wheat flour will result in gluten formation. Gluten allows the development of dough that can expand and retain gas formed from the fermentation of sugars by the yeast.

The expansion of gas bubbles from the fermentation process leads to the formation of the gluten matrix, which stabilizes with the heat of baking, forming the structure and shape of the baked goods. The two basic proteins responsible for the development of gluten are Glutenin and Gliadin. The proportion of these proteins within the different wheat flours determines the main quality and functionality of the flour in the finished baked goods. The higher the content of Gliadin in wheat flour, the higher the extensibility and the lower the elasticity of the dough formed from this flour. On the other hand, a high proportion of Glutenin creates stronger and more elastic dough.

The quality of flour and its performance in baked goods depends on many other factors. The class and variety of wheat normally determine the end use for the flour. Varieties are developed for specific performance of flour in different baked goods.

The quality parameters and performance of wheat flour can be traced back to the field. If for example the wheat is exposed to excessive moisture and appropriate temperature even when in the field it will begin the process of germination. Germination or sprout damage will dramatically affect the composition and performance of flour. Enzymes within the wheat kernel will become active and begin to degrade or change components, such as starch and protein. Flour from sprout-damaged wheat will be inferior and will result in doughs with reduced farinograph absorptions and development time.

In addition the physical properties of the dough will be weakened. Sprouting will increase gassing power and acidity of the dough due to the increase of fermentable sugars in the flour. This will result in breads with higher volumes but gummy and inelastic crumb. The sprouting of wheat can be determined using the falling number. A falling number in excess of 300 seconds will indicate sound wheat while a number below 250 seconds indicates sprout damage. The age of wheat also affects the quality of flour. Flour from freshly harvested wheat does not perform very well.

On the other hand, if wheat is stored for a long time it can result in flour that contains mailard reaction products that will influence its flavour. The milling process, if not carefully controlled, can result in starch damage of the flour.

Tight rolls will result in destruction of starch granules affecting the starch performance. The damage is mainly dependent on the type of wheat and the severity of grinding. Hard wheat flour is more prone to starch damage due to the tight adhesion of the starch granules to protein particles. Starch-damaged flour will result in higher farinograph absorption. It will increase final product volume due to higher fermentable sugars available and enhance the shelf life of yeast-leavened baked goods. However, starch damage is not favourable for other products, such as tortillas, because of the reduction of dough extensibility. Higher starch damage in the flour will result in lower-quality tortillas.

Another issue of flour quality resulting from the milling process is bran contamination. Bran particles in flour due to the presence of the enzyme Polyphenol Oxidase will result in oxidation and darkening of these particles to the extent that it will occasionally resemble microbial contamination. This is prominent in refrigerated cake, muffin and pancake batters. In addition, such contamination will negatively influence the quality of pasta and noodles.

Certain natural antioxidants such as glutathione will also influence performance of flour. Glutathione is present in high amounts in wheat germ, making it difficult to produce wheat germ bread that contains more than five per cent raw germ. Heating of germ will reduce the activity of glutathione to an extent, allowing us to increase the amounts that we can incorporate into yeast-leavened products.

Other issues that could arise with regard to flour quality could be caused by errors such as level of chlorination or enzyme and other treatment of flour at the mill. Chlorination of cake flour is an important treatment that modifies protein and starch, enabling us to produce high-quality cakes in North America. The use of chlorine in food production is not permitted in Europe and some other countries because of the fear of dioxins. Alternative treatments are being researched but are not yet commercially available.

Wheat flour is a very complex ingredient and requires expertise in selecting the appropriate type for the end use. It is also very versatile and can be used for the development and production of a plethora of baked goods and other food products.

Recently the University of Guelph and the Guelph Food Technology Centre offered a four-day course called the Fundamentals of Wheat Flour. The course will be offered again in 2009. / BJ

NOTE: The next several Technical Talks will deal with the basic ingredients for baking. We will examine their function, what is happening with these ingredients and how any new developments affect the baking industry.

Funding for this report was provided in part by Agriculture and Agri-Food Canada through the Agricultural Adaptation Council’s CanAdvance Program. For more information, or fee-for-service help with product or process development needs, please contact the GFTC at 519-821-1246, by fax at 519-836-1281, or by e-mail at  gftc@gftc.ca.

Dr. John Michaelides is director of research and technology at Guelph Food Technology Centre, www.gftc.ca.