Technical Profile: Finding a niche in micromilling

by Emily Buckley
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New micromilling technology opens the door to new food production markets for grain and soybean processors

There is a large demand for micro-milled grain and oilseeds, as the products are easier to use in pro-ducing some foods and may also be easier to digest. Yet the micromilling of soybeans, cereal grains or high-fiber grain fractions such as oat, barley or millet poses serious challenges to millers as these products are usually tough and sticky.

Even specialty milling equipment such as high-speed pin mills or jet mills have great trouble grinding these materials to the required fineness. Normally, this calls for costly processes involving, say, pin mills in combination with air classifiers or grinding under nitrogen. Moreover, throughputs are normally low in these processes.

To allow such materials to be ground to an ultrafine degree, Buhler AG has developed a special rollermill — the Micromill.

MICROMILLING PROCESS

"This machine has recently been developed to damage the cell structure by pressure and friction to improve the digestibility [of product]," said Markus Nussbaumer, manager of specialty milling for Buhler.

Operation of the mill is based on the mortar principle: the machine grinds the material by means of three smooth roll pairs, with one roll in each pair rotating faster than the other. In the narrow roll gaps, the tough kernels are sheared apart by high forces. This ruptures the plant cells, releasing their contents.

Superficially viewed, what you get is micro-flakes with a thickness between 10 and 50 microns. They still consist of coherent cell material that will readily dissolve when subsequently used in foods. (One micrometer, or micron, is one-thousandth of a millimeter.)

[The Micromill] is not comparable to typical rollermills because its finished products are ground nearly five to ten times finer than typical rollermills, Nussbaumer said. (See Images 1 and 2 on page 67.)

Nussbaumer said the Micromill is mainly applied for fatty products, such as oats, soy and millet, that are used in the food industry for ingredient production. The mill’s production capacity is 300 to 1,200 kilograms per hour.

He said the Micromill’s advantage lies in its controlled grinding conditions due to water cooling of the rolls and grinding gap adjustment capabilities that result in uniform finished product quality that is not achieved with a pin mill.

INSTANT SOY POWDER

Nussbaumer said the main application for the Micromill is in soybean milling for products such as soymilk and other dairy products.

The goal of the new process in this application is to produce an entirely natural soy powder that can be used directly in beverages and other foods without requiring any aqueous phase.

For this, the soybeans are cleaned, and then undergo thermal treatment by steam and drying. The soybeans are then hulled and preground. Finally, the material is micro-milled, producing an ultrafine, nutritious soy powder.

CAPTURING VITAL BRAN CELLS

The Micromill could also provide another source of revenue for wheat millers.

Using the Micromill’s patented process, the valuable part of the bran — the aleuron cells — can be extracted in a pure form. The aleuron cells are the vital wheat cells located just underneath the cellulose-containing seed skin and adhering firmly to it.

During normal flour production, they are separated along with the bran fraction. But since they contain valuable proteins, vitamins, minerals and other active substances, extracting them is extremely promising from the nutritional point of view — and could open up additional markets to wheat millers.

However, these valuable cell contents are surrounded by thick cell walls and cannot be assimilated by humans without rupturing the cell walls. Micromilling allows precisely this to be done. In addition, an upstream thermal treatment will improve the taste of the final product.

Buhler said it has already finished installing several Micromill projects in the United States, Europe and in Asia.

The author, Michel Gavin, recently retired as head of the Central Laboratory at Buhler headquarters in Uzwil, Switzerland. For more information, contact Markus Nussbaumer at markus.nussbaumer@buhlergroup.com.

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