Grain-based foods are staples throughout the world. Every day, millions of tonnes of grain are processed in food production plants. In addition to baking flour, dark flour and bran are obtained during grain processing, especially with wheat.
Extrusion technology is a way of further processing flour and the byproducts obtained in the process. Extruders are used in a wide variety of flour processing applications. The most important resulting products are breakfast cereals, baby food, breadcrumbs, croutons, plus modified flours and starches used, for example, as soup or sauce binders or in the bakery industry.
MODIFIED AND STILL A CLEAN LABEL
Modified flours are also called swelling flours, which are characterized by their modified water absorption capacity and their solubility properties. The viscosity of flour-and-water suspensions can be adjusted to the specific applications by selection of the suitable extrusion parameters.
If the correct amount of thermal and mechanical energy is introduced into the product in the extrusion process, this will enable end products to be made which are soluble either in cold or hot water and have a certain bandwidth of viscosities. Swelling flours are used as binders, fillers or freshness extenders in baked goods.
The extrusion process is particularly suited to the modification of flours because it does not require the use of any chemicals. Therefore, these flours are also suitable as ingredients in products subject to a "clean label policy." When using extruded swelling flours, it is enough to declare wheat flour on the ingredient list.
EXTRUSION AS AN ALTERNATIVE
Another possible use is the production of breadcrumbs. Extrusion technology enables breadcrumbs to be produced on the basis of a wide variety of raw materials.
Whereas high-protein flours, such as wheat or rye flours, are needed for developing a gluten framework in the traditional production process, it is basically possible to apply all starch containing products in the extrusion process. This also allows the use of lower-grade wheat flours or corn (maize), rice or potato flours. In this case, the dough is caused to rise on the one hand due to its expansion at the die. On the other hand, dough rising can also be controlled through specific chemical or physical agents.
Fluctuations in the raw material quality are easier to balance in the extrusion process. In addition, it is possible to accurately adjust the texture, color and particle size.
Moreover, extrusion is a highly energy-efficient process. The much lower water content in the product formula in comparison to traditional production, in conjunction with short retention times, ensures low energy costs, especially during subsequent drying.
The energy costs per tonne of finished product – based on a capacity of two tonnes per hour – are twice as high in the traditional process as in the extrusion process. In addition, the extruder offers the flexibility required to produce related products such as baking peas and croutons, or even bread chips, on a given processing line by selecting an appropriate configuration.
EXTRUSION INCREASES VALUE GENERATION
Even very dark flours (low-grade flours) and wheat bran are suitable as raw materials for processing by extruder. Low-grade flours as well as wheat bran are, as a rule, sold at low prices to the feed manufacturing industry. The extruder enables also such byproducts to be upgraded into high-grade foods.
Both byproducts can be processed into breakfast cereals but are also used in a modified form as ingredients in other foods. Bran flakes are highly popular today. Extruded wheat bran, for instance, can fetch double the price of wheat bran in its native form. The opportunities that wheat bran presents as a high-grade food are significant. The high dietary fiber content of wheat bran gives the product an "aura of health."
The basis for making all the products mentioned above is grain flour. This is what the extrusion process has in common with conventional bakery processes.
The difference, however, lies in the dough texture. The dough framework of conventional bakery goods is based on proteins such as gluten and pentosans. The texture of extruded products is based on starch. The raw material must have a starch content of at least 5% to 10% in order to ensure a stable end product texture. The protein content may be low, that is, below 10%.
Flours with such protein contents are typically unsuitable for baking. As the flour price is, among other factors, also influenced by the protein content, low-protein flours are less expensive than high-protein ones. Therefore, the extruder also allows inexpensive flours to be processed.
NEW TWIN-SCREW EXTRUDER
Buhler AG, Uzwil, Switzerland, has introduced a new twinscrew extruder called PRIOtwin, which is designed for continuous production with few product changes.
Thanks to its new modules and its leaner design, it is particularly easy to operate. It combines proven processes using simplified modules, which reduces the capital investment cost. In developing this new design, careful attention was also paid to integrating the extrusion process optimally in the upstream and downstream process stages in order to offer integral solutions with a high customer value.
"The goal of our development efforts was to offer an extruder which would satisfy customers’ needs in the respective segments they are engaged in while still being a much simpler solution than the comparable all-rounder POLYtwin," the company explained.
Christopher Rubin heads the Product Management and Marketing department in the Pasta and Extruded Products business unit of Buhler AG in Uzwil, Switzerland. He can be reached at