Pasteurizing Almonds With Infrared Heat
February 21, 2012 - News
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ALBANY, Calif.—New research from the USDA’s Agricultural Research Service (ARS) Western Regional Research Center has discovered a new almond pasteurizing technique called “sequential infrared and hot air" (SIRHA) provides fast, reliable and relatively economical pasteurization.

According to the researchers, giving almonds a burst of infrared heat, followed by a stint of hot-air roasting, offers a simple, safe, energy-efficient and environmentally friendly way to reduce Salmonella enterica populations to levels generally recognized as safe. Taste tests revealed infrared heating didn’t alter the mild taste, smooth texture, attractive appearance or other characteristics of the almonds.

It’s generally thought that almonds are not naturally contaminated with high levels of Salmonella enterica; however, all almonds processed for sale in the United States today have to be pasteurized in order to kill Salmonella. The pasteurization procedure has to be powerful enough to reduce Salmonella population levels by a 4-log minimum. That’s a 10,000-fold decrease.

For the studies with shelled, roasted almonds, for example, the team targeted a “medium roast," during which almonds’ naturally light shade deepens somewhat. The scientists compared the effectiveness of three approaches: conventional hot-air heating, infrared heating or SIRHA. They found SIRHA was more energy efficient than either infrared or hot-air heating alone.

“With the combined infrared and hot-air heating, we can produce a pasteurized product and significantly reduce roasting time. That should help processors save on their energy bills," the researchers said.

For this work and their newest study with raw almonds, the team used the bacterium Enterococcus faecium as a research model and substitute, or surrogate, for S. enterica. The roasting studies showed, for instance, a more than 5.8-log reduction in E. faecium levels—exceeding the required 4-log minimum. That target was met handily by heating the almonds with infrared until they reached a surface temperature of 140°C, then roasting them with hot air at the same temperature for about 11 minutes. The infrared step took about 1 minute, using emitters—positioned above and below the almonds—that produced 5,000 watts of energy per square meter.

Some packinghouses already use infrared heating, but not for pasteurizing. Instead, it’s part of a wet/dry process to remove almonds’ paper-thin skin, or pellicle, for certain almond products.

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