Understanding heat-treated flour

by L. Joshua Sosland
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The decision by Nestle USA to begin using heat-treated flour for its refrigerated dough products is unlikely to result in a major shift by other flour users to the technology, a range of grain-based foods industry experts told Milling & Baking News last week. Still, the highly publicized move to heat treatment in the name of food safety by the world’s largest food company has generated considerable discussion within and beyond milling.

Confidence that heat treatment of flour for food safety purposes will not become widespread rests on several factors: that the vast majority of flour-based foods go through a kill phase, principally baking, obviating the need for heat treatment of flour; the low level of microbial counts in flour; the adverse effects on flour functionality of heating before baking; and the high cost of heat treatment.

Still, industry executives have been focusing on the issue in the wake of several high profile food product recalls, including Nestle’s recall of Toll House cookie dough.

In that episode, in June 2009, 76 persons were reported as sickened in 31 states after eating the cookie dough. While the product’s packaging warns consumers not to eat the dough raw, it is believed that many consumers in fact do just that. Testing by the Food and Drug Administration found a sample of chocolate chip cookie dough that tested positive for E. coli O157:H7 (though the strain was not confirmed as the one that made the 76 persons sick).

Nestle USA has offered few details about its decision to move to heat-treated flour. Rather than explaining the connection between the move, the company on Jan. 13 said only that the change would “further enhance the safety of our products.”

Responding to an inquiry last week from Milling & Baking News, a spokesperson for the company acknowledged that flour had not been positively implicated as the source of E. coli 0157:H7 in the June 2009 product recall.

Edie Burge, with Nestle USA in Glendale, Calif., said the shift would reduce the potential for E. coli contamination.

“Although we do not know for certain that flour was the source of E. coli 0157:H7, it is a raw agricultural commodity and as such can carry some risk,” she said. “To further ensure the safety of our product, we’ve made a prudent decision to switch to heat-treated flour.”

While Nestle’s move to heat treatment may be adopted by other makers of refrigerated cookie dough, an en masse shift by other flour users is highly unlikely, said Brian L. Strouts, head of research and technical services, AIB International, Manhattan, Kas.

“There is no dispute that heat treatment will lower the overall microbial load of flour, and that can’t be a bad thing,” Mr. Strouts said. “Others have been doing this with cookie dough all along. Nestle’s move may pull additional refrigerated cookie dough producers with them, co-packers who make dough for fundraisers, etcetera.

“Bakers who call me understand that flour is a raw commodity, but they have called to ask, ‘What should flour look like from a micro perspective?’ But refrigerated cookie dough is completely different from most flour uses, bread, snack cakes or even packaged cookies, products that will go through a thermal process, a kill step. I’d be very surprised if there was a move toward heat treatment for most flour-based products.”

As concerns about food safety have mounted in recent years, millers have not sat idly by as spectators. To the contrary, the North American Millers’ Association sought to lay to rest the issue of microbes in flour with the publication in a peer-reviewed journal of an analytical scientific paper.

Toward that end, a working group from NAMA joined with William H. Sperber, a highly regarded microbiologist who has had experience at leading milling companies as well as at non-milling food processing companies.

Published in 2007, the study compared the microbial profile of flour milled in 2003-05 with that of flour milled in 1984-91. Titled “Role of Microbiological Guidelines in the Production and Commercial Use of Milled Cereal Grains: A Practical Approach for the 21st Century,” the paper was published in the Journal of Food Protection.

Among its principal findings were similar or reduced microbial counts overall and substantially lower incidence of Salmonella than in the earlier period.

“Milling cereal grains has a long history of being safe for consumption,” the Sperber/NAMA paper said. “This outstanding record is attributable to the excellent sanitary quality of the milled products and to the baking, frying or cooking of the vast preponderance of milled cereal grains before consumption. Our survey documents an extremely low incidence of Salmonellae and excellent microbiological profiles in the five surveyed products.”

Historically, the focus of microbial attention for millers has been on Salmonella, a bacteria that can cause diarrhea.

The Salmonella reduction to 0.14% of samples was down sharply from 1.05% in the earlier samples.

The study also generated “very low E. coli counts.” According to the paper, many were below the limit of detection.

Notwithstanding this record, the authors understood and even anticipated the questions that could be raised when an incident like that at Nestle occurs.

The review paper noted that a small outbreak of Salmonellosis in 2005 brought the issue into focus and prompted advisory guidance from the Food and Drug Administration.

The incident was associated with cake batter in ice cream in which the batter was not heated before going into the ice cream.

“Because cake batter mixes can contain Salmonella-sensitive ingredients — for example, dried egg or dairy products — it was suspected that the cake batter mix was the source of the Salmonella contamination in this outbreak,” the NAMA paper said.

In response, the F.D.A. issued a bulletin to the retail and food service industries advising that “incorporating an ingredient that is intended to be cooked into a ready-to-eat food that will not be cooked or otherwise treated to eliminate microorganisms of public health concern can pose a serious food safety risk.”

Examples of flour uses that do not feature kill steps include the addition to dehydrated infant foods, seasoning mixes and raw cookie dough used in ice cream.

“To additionally ensure pathogen reduction and food safety, some millers and their customers have developed heat treatments for such specialty uses of milled grains,” the NAMA paper said.

The paper characterized such applications as a “niche” market.

“Such treatments are not necessary for the vast preponderance, millions of tons, of milled cereal grains that are normally baked, fried or cooked before consumption.”

Still, many flour users have been asking about heat treating flour in recent days, according to millers. While food safety concerns have been mounting steadily in recent years, scrutiny has been heightened because of the widely publicized recalls. Pressure on ingredient makers, including flour millers, has been mounting.

“This largely goes back to the Peanut Corporation of America scandal,” one miller said. “Our customers are demanding more and more food safety guarantees, pushing more risk back on the mills.”

According to trade sources, Nestle will be buying flour heat treated at a mill and then storing bulk flour trailers at the company’s plants until further testing is done on the shipped flour. Costs for such procedures could add as much as $8 per cwt to the cost of flour. Costs for heat treatment of flour or grains at a non-milling company that provides the service were estimated at $12 per cwt.

The high cost reflects challenges specific to flour and other dry products. While excellent conductivity makes heat highly effective at killing microbes in water, poor conductivity makes using heat on flour a challenge.

“At 160 degrees in a matter of seconds you kill microbes in water,” the miller said. “It takes a few minutes in gravy and in flour, it could take hours to get enough heat to them to kill them. Dryness works against you.”

Beyond the cost, the effects of heat on flour are substantial, the miller added.

“When you heat flour, what are you doing to the gluten properties?” he asked. “Are you changing or destroying them? If you take bread flour, chances are you will devitalize the gluten. It will still have the protein but it may not have the visco-elastic properties needed for the loaf to rise and hold its shape.”

While millers who offer heat treatment said that even bread flour may be heat treated successfully under certain circumstances, the process is a difficult one and requires considerable formulation work for the finished product.

Questions of whether microbial counts could be reduced in cereal grains have been posed for decades, Dr. Sperber said.

“Numerous researchers have evaluated processes for the reduction of microbial counts in milled cereal grains,” the NAMA paper said. “Such reductions are not easy because it is considerably more difficult to kill microbes with dry heat than it is with moist heat. Furthermore, the process must not significantly degrade product quality or functionality.”

Apropos of Voltaire’s admonition against making “the better the enemy of the good,” Dr. Sperber cautioned millers and flour users to carefully consider the cost and benefits of further reductions.

He explained, “It may be interesting to speculate how much additional reduction in the microbiological profiles of milled cereal grains might be achieved in the future, it might be better to ask, in the interests of public health and food safety,’ is a greater reduction in microbial counts of milled cereal grain necessary?’”

According to the NAMA paper, part of the confusion around food safety measures for flour relate to difficulties in easily categorizing milled products.

“Even though milled cereal grains are included in the definition of processed foods because of the dry-milling process, they are only one small step removed from the definition of a raw agricultural commodity,” the paper said. “Milled cereal grains are not processed in the same manner in which, for example, raw milk is processed by pasteurization in order to reduce its microbiological load and eliminate pathogenic microorganisms that might be expected to be present. Processes such as cooking and canning, as included in the definition above, kill all of the vegetative microorganisms originally present in the raw foods.”

This confusion aside, the NAMA paper said the food safety characteristics of flour are very high.

“It is accurate to claim that the microbiological profile of milled cereal grains is rather similar to that of some of the more highly processed foods that are subjected to more rigorous process treatments, including cooking,” the NAMA paper said. “There is no public health or food safety benefit to be derived from further reductions in the microbiological profile of milled cereal grains. Of course, the dry milling industry will maintain and improve its sanitation procedures…. Microbiological monitoring guidelines are used to verify the sanitary conditions of the milling and transportation operations.”

Richard C. Siemer, president of Siemer Milling Co., Teutopolis, Ill., said it would be “unbelievably disruptive” if his customers were to shift widely to heat treated flour. He estimated his daily heat treatment capacity at 1,000 cwts, a small fraction of the company’s 28,700 cwts of total daily milling capacity.

“I think as a practical matter, the food safety issue should not be a concern for most flour users,” Mr. Siemer said. “We are selling heat-treated flour for low-micro uses, but mostly for other, higher-value products. The need for microbial control in some applications is real, but limited.”

Industry sources expressed concern that a clash was emerging between consumer expectations of pathogen free food and the reality that microbes may be found on all raw foods from fruits and nuts to meat products.

Elizabeth A. Faga, NAMA president, noted the difficulties associated with the issue but was upbeat about milling’s role in food safety.

“Food safety is a farm to plate challenge and responsibility,” she said. “The milling industry takes seriously our responsibility to ensure that the foods produced in our mills are safe and are not compromised in any way. We have multiple food safety methods in place. We are committed to working with customers, researchers, regulators and other experts in the field to ensure the integrity of the food supply chain.”

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