Heating up flour

by Chrystal Shannon
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Flour treatment is a value-added process that millers might consider to extend into niche markets.

Flour heat treatment (FHT) is a process developed in the early 1990s originally to produce batter flour with high viscosity and low bacterial count. Today, heat-treated flour is used in a variety of food applications, such as breadings; batters and coatings; soups; sauces; thickeners; baby foods; and biscuit, wafer and cake flours. Heat-treated flour also is used as binders, such as in sausage products, as carrier flours for pre-mixes, as admixture flours for special recipes in ready mixes and as partial starch replacement.

"FHT flour is a value-added product with good margins for the millers," said Hansjoerg Haldner, product manager of value-added processes, Buhler AG, Uzwil, Switzerland.

Most of the companies producing FHT flour are traditional milling companies that have extended their activities into value-added and niche products, he added. "FHT means new opportunities for the millers," Haldner said. "The response depends on the country, the specific food market requirements and the milling tradition. In countries where there is a good link between the mills and the food industry, heat-treated flour has great success."

The FHT process modifies the physical and rheological properties of the flour. Gluten can be shortened or denatured. With the gelatinization of the starch, the hot and cold viscosity is modified to obtain a desired value. Bacterial count also can be reduced.

The FHT process involves heating the flour, steam and/or water addition, temperature stabilization, drying, cooling, sifting and grinding and homogenization.

"These processes can take place online as the flour, germ or bran are coming directly off the mill and involve thermally treating the product," said Marty Legein, director of business development, CETEC Cereal Technologies Inc., Millersville, Maryland, U.S. CETEC is the North American representative for VOMM, a Milan, Italy-based manufacturer of FHT equipment.

VOMM has been involved in flour drying since the early 1970s and today produces a variety of flour heat treatment equipment.

Legein described the flour heat treatment process:

"The dryer’s jacketed cylinder is either heated by steam or diathermic oils to temperatures as high as 320º C. As the product enters the chamber it is uniformly centrifuged onto the internal heated walls and mixed in co-current with forced heated air. This allows for extr emely high temperature and a short resident time. The product is then cooled and separated from the moist air using a series of cyclones and filters.

"A secondary process is used when flour gelatinization or starch modifications are required. This involves a preliminary short precooking process followed directly by the above-mentioned drying."

Buhler’s FHT process involves a differential dosing scale that feeds the flour at a continuous rate to the process. In the subsequent conditioner, energy is added in the form of steam and water. Heated retention screws define the process time.

"The most important process parameters are throughput, steam quantity, water quantity, process temperature and process time," Haldner said.

Depending on the specific type of treatment, all process parameters can be separately selected.

The downstream thermopneumatic conveyor adjusts the desired moisture content of the treated product after the process. In the treatment of high viscosity flours, the flour is sifted after the thermal process and ground to a defined particle size.

After the process, the finished product passes through a homogenizing bin and is then transferred either to a storage bin or directly to the bagging system.

The cost of the FHT process depends on the type of end product the miller wishes to produce but ranges from U.S.$500,000 up to U.S.$2 million.


Heat-treated flour is currently produced in European countries, including the United Kingdom, France, Italy, The Netherlands and Germany, as well as in many Asian countries, Haldner said.

The FHT process is widely used in the U.K. since the use of chlorine as a flour-bleaching agent was phased out beginning in November 2000.

The issue over chlorine was never really one of safety, according to Terry Sharp, head of the Baking and Cereals Processing Division of Campden & Chorleywood Food Research Association, Chipping Campden, U.K. "E.U. regulators wanted positive proof that there was no possible harm (using chlorine as a flour treatment), but the milling industry took the view that proving that would take too long and be too costly," he said.

Therefore, by default, the use of chlorination as a flour improver was no longer acceptable in the E.U. This had important ramifications for U.K. bakers since chlorine had been used for more than 60 years in the production of high-ratio cakes — products with higher levels of sugar and liquor.

"Recipes had developed to the extent that it was impossible to use untreated flour without significant changes," Dr. Sharp said.

The CCFRA examined the possible options available to the industry, including the baking of a selection of cakes using the standard CCFRA test bake recipe as a base. The conclusion was that there were just two solutions: replace flour chlorination with a heat treatment process or use untreated or heat-treated flour in combination with some specialized ingredients. Neither alternative was an exact replacement for chlorinated flour, the CCFRA noted.

This report, completed in late 2000 just before the ban on chlorination went into effect, noted that the performance of heat-treated flour in cake making was only approximately 95% that of chlorinated flour. "Different processes produce flours with different end moisture contents, making it particularly difficult for a baker to switch between millers," the report said. "Also, if the heating process is not optimized, then the flour can contribute a slight cooked flavor to the finished product. In the samples tested, this was not unpleasant and may only have been noticed in a direct comparison with the chlorinated control."

Paul Catterall, biscuit and cake section manager for CCFRA, recently told World Grain, "Heat-treated flour has continued to develop and is better now then it was, but we do still hear of bakers who are having occasional problems."

According to Buhler’s Haldner, a further advantage to heat-treated flour is that it is a natural product with no additives.

CCFRA recently completed a research project that looked at how FHT affected the characteristics of the flour so bakers didn’t have to test bake all the time. The project was funded by U.K. millers, and the results are embargoed for several more months. But Sharp said the CCFRA was "reasonably successful" in its objectives.

Although there are no plans to ban the use of chlorine as a flour bleaching agent in North America, some mills have experimented with flour heat treatment, acknowledged James Bair, vice-president of the North American Millers Association, Washington, D.C.

"Chlorine is always under attack by environmentalists, not so much for its use in milling but because of the presence of PCBs (environmental pollutants Polychlorinated Biphenyls), so it is always being scrutinized very closely by regulators," Bair said.

Any ban on chlorine in North America also would have consequences for American bakers. American-style wedding cake or angel food cake — products that have high quantities of sugar and softer texture — rely heavily on chlorine treatment, Bair said.