Salmonellosis outbreak from ’95 does NOT support humidity as a critical parameter in jerky processing

I just had a rather enlightening conversation with a senior USDA-FSIS official about the need for humidity during jerky manufacturing.

I asked, “How does humidity destroy pathogens?”

The official really didn’t know the answer, but he did state that, without humidity, pathogens can become heat-resistant, and Salmonella can grow and survive normal lethality.

When I asked for the studies that backed up these statements, the official pointed to the same studies they always do. I then explained how those studies didn’t actually take product to lethality (i.e., what was surviving was only surviving longer than the non-treated Salmonella). The official countered by citing the salmonellosis outbreak from 1995 in New Mexico — as is typical of this conversation.

Here, too, the problem with citing that case is lethality, as the product implicated in that outbreak should be considered a raw beef jerky, not fully cooked.

Per the published outbreak report by the CDC (https://www.cdc.gov/mmwr/preview/mmwrhtml/00039423.htm), partially frozen product was placed on racks and was pushed into a drying room. The chamber temperature (not the product’s internal temperature) was set at 140 F for three hours, then reduced to 115 F for approximately 19 hours. Therefore, the product was never exposed to a lethality treatment, and hence, by definition, it was a raw product. The report also states that no product temperatures were ever recorded.  

I promised to send the official the CDC report to remind them (or make them aware) that the production technique that was used resulted in a raw product that clearly wasn’t ready to eat (and that doesn’t even factor in other inputs or lack of them, such as sanitation, equipment, plant elevation, etc.).

It’s a shame this conversation even needed to happen, and that we have to point this out about a case more than 25 years in the past. However, it’s not the only time we’ve had these conversations lately — we have been seeing more and more actions by USDA-FSIS around humidity requirements based on these incorrect assumptions and faulty arguments. When we bring up actual science around heat resistance and pathogen growth, little discussion occurs, and FSIS inevitably falls back on the New Mexico outbreak as their “final answer” for why humidity is needed in jerky processing.

Is humidity during processing a control factor? Yes, as it assists in heat transfer. When you are measuring the internal temperature of a product, you are, in fact, measuring the transfer of energy into the product. One way to increase the rate of transfer is to increase the humidity in your cooking vessel.  At home, when you boil something, it cooks faster than it would if you cooked it in a pan, given the same energy input. But that doesn’t make humidity a critical parameter, it makes it a supporting parameter. The critical parameter is the rapid transfer of energy into the product to denature the proteins of the pathogens, rendering them non-viable (killing them). You measure this energy transfer by using internal product temperature monitoring devices.  

The entire paradigm of “chamber” temperature and “chamber” humidity now falls on a very niche part of the industry (who implement and know their process — and make some great products!). It doesn’t apply to the vast majority of the industry making jerky or other shelf-stable products.

HACCP is about analyzing for hazards, not creating a plan and then making products. Know your process and apply your controls, and you’ll be in great shape.

However, unless you want to spend a lot of time arguing with regulators, point to the sentence in the 1999 version of Appendix A, which allows you to rely on a sealed oven during cooking as the evidence of how you deal with heat transfer. I promise you that it will be a lot less frustrating!

— Andrew Lorenz, president, We R Food Safety!, andrew@werfoodsafety.com