Friends of the blog Scott Gottlieb and Frank Yiannas posted a statement to FDA’s website today detailing the findings of the agency’s investigation into over 50 E. coli O157 illnesses in the fall of 2018.

Today, we’re announcing the findings of this investigation and our best hypotheses as to how this contamination could have occurred. In the case of the one farm with a positive sample previously referenced, the FDA believes that the most likely way romaine lettuce on a specific ranch on this farm became contaminated was from the use of water from this reservoir as agricultural water. It is believed that this water came into contact with the harvested portion of the romaine lettuce, since the outbreak strain of E. coli O157:H7 was found in sediment from the reservoir and in no other sampled locations. The water from the reservoir doesn’t explain how lettuce grown on other ranches or farms identified by traceback may have been contaminated. So, this one farm cannot explain the entire outbreak.

The full report can be found here.

My favorite part is this recommendation from investigators:

Perform a root cause analysis when a foodborne pathogen is identified in the growing environment, in agricultural inputs (e.g., agricultural water or soil amendments), in raw agricultural commodities or in fresh-cut ready-to-eat produce. The goal of a root cause analysis is to determine the likely source of the contamination, if prevention measures have failed, and whether additional measures are needed to prevent a reoccurrence.

From my experience, this root cause analysis approach is hit or miss when pathogens are found during routine sampling (but maybe a barfblog reader can provide me with some details on whether they know of folks doing this).

My friend, PIO extraordinaire and around great guy Matt Shipman asked Natalie and I about electric pressure cookers a couple of weeks ago, he was interested in answering questions that folks may have about whether they are safe to use. Here are the results of our conversation.

Electric pressure cookers, like the Instant Pot, have grown in popularity in recent years. One reason for this is that they allow people to prepare meals more quickly. But a lot of people aren’t sure why electric and stovetop pressure cookers prepare food faster than conventional stovetop cooking. And many people also wonder whether pressure cookers are actually safe.

You have questions, we have answers.

Why does food cook more quickly under high pressure? (Or, why does food cook more quickly in an Instant Pot?)

Let’s talk about heat.

Hot air rises. So, when you cook in a regular pot on your stove, a lot of the heat escapes. When moisture in the food turns into steam (which happens at 212 degrees Fahrenheit if you’re at sea level), a lot of that moisture also escapes through evaporation.

But when you’re cooking in a pressure cooker, there’s nowhere for that hot air and steam to go – it’s trapped.

“Because the hot air and steam are trapped, a pressure cooker allows you to heat the moisture – steam and water – above its normal limit of 212 degrees Fahrenheit,” says Ben Chapman, a food safety researcher at NC State University. “And the pressure cooker traps that hot air and moisture with the food, which expedites the cooking process.

“In other words, the moisture surrounding the food itself reaches higher temperatures than it would without the pressure, which speeds up the chemical processes involved in cooking. But the food doesn’t dry out like it would in an oven or on a stovetop, because the moisture has nowhere to go.”

Are pressure cookers risky to use?

No, not usually.

Air and steam expand as they heat up. So, if no hot air and steam is allowed to escape, a pressure cooker can explode.

“Most modern pressure cookers have a safety valve that is designed to release hot air and steam when the pressure inside the vessel reaches a certain point,” Chapman says. “Once the pressure has been relieved, the valve shuts again.

“Modern pressure cookers should also have a release valve that allows you to vent hot air and steam before opening the lid. That’s important, because you don’t want the lid to fly off, or to get scalded by steam when you open the lid. (Even with the release valve, it’s a good idea to open the lid away from you.) In some models, the safety and release valves are located in the same part of the cooker.”

Can I cook frozen food in a pressure cooker? 

You can cook frozen food in anything. The real question is: “Is it safe to cook frozen food in a pressure cooker?” And the answer is yes.

“The food safety concern here is that you don’t want foods – like raw meat or poultry – to be in the temperature ‘danger zone’ for a long time,” says Natalie Seymour, a food safety extension associate at NC State. “That can happen if you’re cooking frozen foods in a crockpot or a slow cooker, or even in the oven.

“The danger zone is between 41 degrees and 135 degrees Fahrenheit (5-57.2 degrees Celsius), which is the temperature range that promotes pathogen growth,” Seymour says. “It’s also the temperature range that allows pathogens to produce toxins that can persist even after the temperature gets high enough to kill the pathogens themselves. Just killing the pathogens won’t make food safe if they have already created heat-stable toxins.”

In short, you can cook frozen food safely using anything, as long as you monitor the temperature to ensure that it spends less than four hours in that temperature “danger zone.” That can be challenging if you’re using a slow cooker.

“However, because of how they work, pressure cookers do a good job of getting foods through the temperature danger zone pretty quickly,” Chapman says. “That makes it safe to cook frozen foods in a pressure cooker.”

What’s the difference between a pressure cooker and a pressure canner? Can I use them interchangeably?

Pressure cookers and pressure canners are not the same thing, and you shouldn’t think of them as being interchangeable. A good rule of thumb is that you can use a pressure canner as a pressure cooker, but you cannot use a pressure cooker as a pressure canner.

“Pressure canners have to be able to reach and maintain a consistent internal temperature of 240 degrees Fahrenheit (115.5 degrees Celsius) in order to inactivate the spores that cause botulism poisoning,” Chapman says. “But pressure cookers are variable and often don’t reach temperatures of 240 degrees. Also, electric pressure cookers – like Instant Pots – run on a cycle, in which the internal temperature rises and falls. That means they can’t be used as pressure canners.”

Note: You can find additional resources for pressure canning here.

Foodborne pathogens seem to like lots of nut butters. This week’s pathogen in nut butter news comes to us from Thrive Market and surprise, it’s Listeria, not Salmonella.

According to Thrive Market, all unexpired lots of their nut butters after a supplier identified some Lm in the products. I guess the expired ones are okay? Expiration dates are really for quality anyway – and we don’t really have expiration dates, but whatever.

Thrive Market, Inc, is recalling all unexpired lots of the Thrive Market-branded nut butters listed below (“Product(s)”) due to the potential for contamination with Listeria monocytogenes. On January 21, 2019, one of our suppliers notified us that it was issuing a recall of all nut butters it has manufactured since January 2018 because of a positive test for Listeria monocytogenes in recent lots. Because the safety of our members is our absolute priority, we are expanding on our supplier’s recall and are voluntarily recalling all unexpired lots of all Thrive Market-branded nut butters manufactured by this supplier.

The public health impact of the contamination isn’t really clear to me – how much Lm? Are nut butters protective in the gut to Lm like they are to Salmonella? Not sure. That’s a  question for another day.