The apple that fell on Newton’s head led him to develop the theory of gravity, but hazelnuts falling from trees in Oregon this autumn came loaded with a different message – that the nuts could be dangerous.


For the first time, hazelnuts were implicated in a foodborne illness outbreak, making at least seven people sick from E. coli O157:H7.  Unshelled nuts, or filberts, were found to be contaminated, and it is thought that consumers transferred E. coli bacteria from the shell to the nut meat as they cracked open the nuts.

There have been other food poisoning outbreaks associated with nuts – notably almonds, pistachios and peanuts. Since 1990, whole nuts (both shelled and unshelled) have been confirmed as the source of six outbreaks, according to the Centers for Disease Control and Prevention Outbreak Database. 


But the recent E. coli outbreak from hazelnuts, which had been distributed in December of 2010, raised questions about whether current methods used to grow and process nuts can ensure that they are safe to consume.

The nature of how many nuts are harvested puts them at risk for contamination.  Most are shaken to the ground and swept up by machine. While on the orchard floor, nuts can come into contact with harmful bacteria in soil or animal feces. Bacteria grow especially quickly on nuts that fall into a damp environment.

Nut growers have long been aware of this problem. “We’ve always washed and dried our product as fast as possible,” says Polly Owen, manager of the Oregon Hazelnut Marketing Board. Getting nuts off the ground, rinsed and dried quickly narrows the window of time in which bacteria can grow on them. And until the recent outbreak, Owen says hazelnut growers had been under the impression that this rinsing and drying process was enough to eliminate bacteria.

However, the hazelnut industry is now re-examining its harvesting and washing process. “At this point, on the in-shell, we’re going, ‘OK, maybe we need to go a step further on that’ and really concentrate more on effective wash lines and that sort of thing,” says Owen. 

The almond industry is all too familiar with concerns over contaminated nut shells. In 2000 and 2004, two outbreaks of Salmonella Enteriditis linked to whole, raw almonds sickened 177 and 47 people, respectively.

Joseph Connell, Farm Advisor for University of California Cooperative Extension of Butte County, explains that the most likely source of the almond outbreak was bacteria being transferred from nut exteriors to exposed meats on the conveyor belt.

“The concern was that, if the orchard had a problem in the first place, then the outer part of the nut, the shell or the hull, had some contamination, and when the processing took place, apparently some of that contamination got onto the nut meat as well,” says Connell.

In 2007, to address the risk of distributing potentially contaminated nut meats, the Almond Board of California worked with the US Department of Agriculture (USDA) to implement a rule requiring that a bacteria “kill step” be performed on nut meats before sale. This step could include traditional methods of preparation, such as blanching, dry roasting or oil roasting, or a variety of other processes designed to preserve the original flavor of the nut, including various steam methods, heating methods, and fumigation with propylene oxide (PPO), according to Tim Birmingham, Associate Director of Food Quality and Safety for the Almond Board.

Many growers put up strong resistance to this law because it prohibited them from producing raw almonds, which they say generally sell for 40 percent more than treated almonds. They also argued that applying heat to almonds changes the taste of the nut and can kill essential nutrients. In addition, PPO, the most common method of almond sterilization, is a suspected carcinogen.

In 2010, the U.S. District Court of Appeals in Washington D.C. allowed a lawsuit filed against the USDA’s rule by 10 California growers to go forth, after the USDSA attempted to prove that growers did not have the right to contest the law.

In the meantime, Birmingham says, the mandatory pasteurization rule is still in place.
And the almond industry has taken other steps to ensure that almonds are safe even before they leave the orchard for processing. After all, Birmingham says, pasteurization only kills a certain level of bacteria. “If you have higher levels coming in, the pasteurization process won’t be sufficient.”

McConnell explains that, to keep the orchard floor dry, growers now plant trees farther apart and keep them pruned so that sunlight can reach the ground, where it not only kills bacteria in the soil but dries nuts quickly. The industry also recommends against the use of organic manure, which can carry harmful bacteria.

According to McConnell, these steps have made a significant difference in the safety of the almond growing process. “By combining those two things, that pretty much solved most of the problem in the field.”

Birmingham cites other safety measures that have been put in place since the outbreaks earlier last decade, such as monitoring water quality, keeping harvesting tools and machinery sterilized, and removing any animal carcasses found in the orchard.

As for the hazelnut industry, Owen says it will be re-examining its washing processes. Right now, hazelnut growers use a variety of different washing techniques. “We’ll be standardizing [washing methods] a little more,” she says,” to have something where I can sit here and say, “They’re all doing one of three things, and this is exactly what it is.”

She says the Hazelnut Board plans to turn to other industries as models.  “The world is open as to what we’re going to be looking at so that we can make sure we’re up to speed on the best and the most efficient methods for ensuring that in-shell is clean,” she says.

One washing technique Owen offers as an example is the use of ozone gas, which is formed from surrounding air, shot into wash water, and then dissipates back into the environment. “It’s a very good agent for taking care of bacterial contamination,” Owen says.

Meanwhile, Owen hopes consumers won’t hesitate before buying nuts from the bulk section. She says the industry has always been aware of the importance of food safety, and launched an initiative in 2009 to train growers and processors in reducing risks associated with foodborne pathogens.  The recent outbreak was an “isolated incident,” she says, an incident that will cause the industry to “ramp up even quicker our look at that in-shell product.”

And regardless of the steps taken by nut producers to ensure the safety of their products, consumers can help ensure their own safety by washing their hands after shelling nuts before eating the nutnmeats. This will reduce the chance of transferring any bacteria that might be on the outside to the inside.