A combination of hot air roasting and infrared heat may provide a new, more efficient method of almond pasteurization to eliminate harmful pathogens such as Salmonella, according to researchers at the U.S. Department of Agriculture’s Agricultural Research Service. The method, which is ready for commercial-scale adoption, would help processors abide by rules that require all almonds sold in North America to be pasteurized.


Since Sept. 1, 2007, the Almond Board of California has required all almonds — including those labeled as ‘organic’ — to receive some type of wash or heat treatment to eliminate potential pathogens on their surface. In 2003 and 2004, at least 29 individuals in the U.S. and Canada became ill in a Salmonella outbreak linked to almonds distributed by Paramount Farms and sold at Costco.

Under development for four years, the USDA’s new method introduces infrared heat to the roasting process for roasted almonds, reducing roasting time while heating the almonds to temperatures that should eliminate Salmonella well beyond the required 4-log — or 99.99 percent — minimum reduction. In fact, studies on the method showed a 5.8-log reduction of a type of bacteria that behaves similarly to Salmonella.

USDA engineer Zhongli Pan, Ph.D., and USDA microbiologist Maria Brandl, Ph.D., headed development of the method with the intent to improve pasteurization without adding burdensome costs or time investments.

“When we develop new technology, we consider first how to scale it up for commercial use,” Pan told Food Safety News. “This is something new that’s a more sustainable, energy efficient alternative to the current technology being used.”

Current methods of almond pasteurization use either chemical washes or steam, while the USDA’s method relies only on infrared heat emitters, a technology Pan said was easy to install in existing almond processing facilities. The fact that the method doesn’t use chemicals or water makes it more environmentally friendly, as well, he added.

According to volunteer taste testers, almonds treated with the infrared method do not taste, feel or appear any different than other almonds.

Pan said the USDA is now working with processors in California to implement this method in their facilities, which he said will end up costing them less money and saving them time. All of the almonds sold in North America — and 80 percent of almonds sold around the world — come from California.

The method also works on other types of nuts, he added, though almonds are the only nut with rules that require pasteurization.