Remember watching Grandma steadily turn the crank on the flour sifter as she made the pumpkin pies for Thanksgiving? Ever think about why she was sifting the flour for the pie crust?

"She was making sure that only flour, and no insects, went into those pies," says Jim Bair, vice president of Millers' National Federation. "We in the milling industry are also concerned with quality. Our aim is to produce wholesome food products in a sanitary environment."

And with the help of methyl bromide, the milling industry has been doing that for years. Compared to other users in the agricultural sector, the milling industry is one of the smallest users of methyl bromide. But that use is a vital one, and in just a short time, methyl bromide will no longer be available.

"For years we've been trying to reduce our reliance on methyl bromide," Bair comments. "We use this chemical, which never touches our wheat or flour, to fumigate our milling structures with the idea that it's better to kill the pest before it reaches our products. And, we use only a fraction of what we're allowed to use. Although we've tried heat, CO₂, phosphine, and a combination of alternatives, we've found no single replacement that works as effectively as methyl bromide. This chemical allows the milling industry to comply with the Food and Drug Administration's (FDA) stringent regulations that mandate the sanitary conditions to ensure U.S. consumers wholesome, insect-free flour."

Insects can enter the mill in different ways, one of which is to come in with the grain.

But, Wendell Burkholder (ARS-Madison, Wisconsin) along with scientists from the University of Texas and Biotect, Inc., developed and patented a technique to detect insects in grain. This test can not only find live or dead insects, but can also detect insect fragments. The Millers' National Federation financed a grant to the University of Texas to support this effort. The test—which is close to commercialization—will, for the first time, allow millers to test grain before it reaches the mill. Millers now buy grain that gets dumped from railcars, hauled to grain elevators, and conveyed to the mill. If an insect is discovered at the mill, it would create difficulties. The new scientifically based ELISA (enzyme-linked immunosorbent assay) test allows millers to use a probe on the grain to check for insect infestation while it is still in the railcar. The test works on a variety of grain and milled grain products, including wheat, rice, barley, oats, and corn.

"If the miller finds insects at the railcar site, then the grain can be rejected," Bair says. "This puts the responsibility of keeping grain free of pests with the grain shipper and ultimately, the producer, who can do it more effectively and economically."

The milling industry, USDA, and universities recently completed a major study to compare this new test with current methods used by USDA inspectors (and sanctioned by FDA) in which the inspectors take a sample of grain, put it under a microscope, and count the number of insect fragments found in the sample.

How a Mill Is Fumigated

Methyl bromide is used to fumigate the physical structure of a mill and the equipment used in processing grain into flour. Fumigation is usually done twice a year, over a 3-day weekend to minimize downtime. Before the process begins, the flow of wheat from the storage facility to the mill is cut off. All grain residues are cleaned from milling equipment, which is left open for maximum exposure to methyl bromide. Since dust and grain particles affect the effectiveness of the treatment, the mill is thoroughly cleaned. Empty bins and bulk storages are also treated. At this point, no one is allowed in the building other than those applying the chemical. The building is then sealed to prevent escape of the methyl bromide.

"Only outside contractors or mill employees who are trained, certified, and licensed can apply the methyl bromide," Bair says. "Although EPA authorizes use up to 6.0 pounds per 1,000 cubic feet, we normally use only l to l.5 pounds per 1,000 cubic feet, depending on the tightness and structural integrity of the building. An average flour mill contains between 1.5 million and 2 million cubic feet."

The methyl bromide gas is held in the mill for 24 hours, when certified personnel enter to begin the aeration process. Only after the air has been tested to ensure safety are workers allowed to enter the mill to remove the sealants and ready equipment and the mill for normal operation.

After startup, flour milled in the first 30 to 60 minutes is diverted into byproduct storage. This ensures that any residue which might linger in the equipment is not destined for human consumption.

Other Alternatives

High heat treatments have shown promise as an alternative to methyl bromide fumigation in certain facilities, Bair reports. But, some of the flour mills in the Untied States are more than 100 years old. Some of these mills are not structurally tight enough to effectively withstand raising and holding the temperature at high levels. Neither do they have the heating capacity to raise the temperature to levels that would kill insects.