In August 2026, AAFCO determined their official definition of HPP (High Pressure Processing). As is common with AAFCO Definitions, it left much to be desired by way of clarity. Chelsea Kent sent the following letter to Justin Hill, who led the team that ultimately wrote the new official definition, to request improvements to the definition that will ensure correct methodology is used by all who choose to adopt HPP as standard practice.
Dear Justin Hill,
Amy from Hills recommended that I reach out to you following the AAFCO meeting regarding the newly accepted definition of High Pressure Processing (HPP):
“High Pressure Processing, HPP. (Process) A non-thermal preservation technique that applies high hydrostatic pressure to foods to reduce or inactivate vegetative microorganisms, certain parasites, and certain viruses with effectiveness dependent on pressure, time, temperature, and product characteristics.”
I very much support defining HPP. At the AAFCO meeting I did voice my concern that the current definition may unintentionally legitimize practices that do not conform to the validated methodology for HPP as a pathogen-control intervention.
I mentioned that post-HPP package opening is common in the commercial raw pet-food industry – more importantly, it’sstandard practice with all but 2 of the top HPP’ed “raw” manufacturers doing it, to my knowledge. The response suggested that the committee was not aware this was occurring. Because this substantially changes the food-safety implications of the process, I wanted to provide additional information and a scientific resource who can help verify it.
1. Actual industry practice
Commercial HPP is performed after food is sealed in high-flex plastic packaging. The primary advantage of HPP occurs because the treated food is not subsequently exposed to environmental recontamination.
However, currently products are HPP-treated in large bulk logs or intermediate packaging. The HPP package is then opened and the product is subsequently ground, formed, portioned, dehydrated/freeze-dried, and/or repackaged into its retail configuration.
I am happy to share video footage of this practice if you would like. Only two manufacturers adhere to the correct methodology and HPP-ing in the final packaging.
Though the methodology clearly starts that opening the package after HPP eliminates the protection against post-process recontamination that in-package HPP provides.
This is also consistent with the framework already established under 21 CFR Part 507. FDA requires animal-food hazard analyses to consider processing procedures, packaging, transportation, storage/distribution and environmental exposure, and specifically requires consideration of environmental pathogens where food is exposed before packaging without a subsequent control. Sanitation controls must also prevent cross-contamination from raw to processed product. Literally 100% of those hazards become a concern in violation of the rule when this practice occurs.
Dr. Mary-Grace Danao addressed this issue directly in her AAFCO HPP presentation:
“Can we use HPP to extend the shelf-life of the product only? Yes, so long as you have a lethality step (e.g., sous vide cooking) and data that shows you have adequately controlled for pathogens and, potentially, a means to control for L. monocytogenes if you have a post-lethality exposed product that could have been re-contaminated (e.g., grinding and forming after HPP).”
Therefore, “food underwent HPP” and “HPP is a validated preventive control for the finished food” are not necessarily equivalent statements.
USDA-FSIS similarly distinguishes HPP used as a pathogen intervention from HPP used merely for quality or shelf-life purposes, reinforcing the importance of what the process is validated and relied on to accomplish.
2. Why an incomplete definition may be worse than no definition
My concern is not that HPP is inherently problematic. Properly validated HPP can be a valuable food-processing technology.
The problem is that defining HPP only as the application of pressure can create a regulatory and consumer shorthand:
“HPP-treated” = pathogen controlled.
That conclusion cannot be made from pressure alone and when it is not done in accordance with the methodology it becomes potentially dangerous and misbranded/misrepresentative of safety.
HPP efficacy is affected by the food matrix and process conditions. Research performed at the University of Nebraska under Dr. Danao has demonstrated, for example, that fat concentration can alter microbial inactivation and recovery following HPP. Yhuliana Niño Fuerte’s 2024 work specifically demonstrated a pressure-fat interaction in Listeria inactivation and concluded that additional data are required to build broadly applicable predictive models.
Other important variables include water activity/moisture, pH, starting temperature, pressure, hold time, packaging, target organism, storage temperature and post-process handling.
If the definition allows any chosen application of high pressure to be perceived as equivalent to validated HPP pathogen control, manufacturers may receive regulatory or marketing credit for an intervention whose validated operating envelope was never established—or was subsequently invalidated by opening and reforming the food.
This could paradoxically reduce food safety by:
– encouraging regulators to treat “HPP” as a proxy for microbial safety rather than examining the complete preventive-control system;
– creating a false sense of safety for regulators, consumers and downstream manufacturers;
– obscuring post-HPP environmental contamination hazards;
– allowing significantly different pressure/time/product conditions to be marketed under the same terminology;
– overlooking recovery of pressure-injured organisms during subsequent transport and storage;
– extending shelf life—and therefore potential recovery time—without validating safety through the intended shelf life and distribution conditions; and
– focusing regulatory attention disproportionately on manufacturers that do not HPP even though HPP itself does not compensate for an inadequately validated or post-process-exposed manufacturing system.
3. Suggested definition
I know that writing definitions is a complicated job that is burdened by research and blind spots in real life application. I am not trying to write a definition but I hope this is helpful in moving necessary revisions forward.
I would suggest language along these lines:
High Pressure Processing (HPP). (Process) A preservation process in which food is subjected to high hydrostatic pressure for a defined period to reduce or inactivate susceptible microorganisms.
When HPP is represented or relied upon as a microbial preventive control, the process shall be scientifically validated for the specific food or a defined validated operating envelope, considering as applicable pressure, hold time, initial and process temperature, product composition, pH, water activity/moisture, fat content, target microorganism, microbial load, packaging configuration and integrity, and intended post-process storage and distribution conditions.
HPP intended as a terminal pathogen-control treatment shall be performed in packaging demonstrated suitable for the validated pressure cycle and maintained closed following treatment. If the food is exposed to the environment after HPP through opening, grinding, forming, cutting, blending, drying, freeze-drying, repackaging or similar processing, hazards associated with post-HPP exposure shall be separately controlled by a scientifically validated preventive control where necessary.
Products or formulations processed under the same HPP cycle must each fall within the validated operating envelope; use of a common pressure/time cycle alone shall not establish equivalent microbial lethality among differing formulations.
The validated process shall include appropriate post-HPP handling, storage, transportation, temperature and package-integrity requirements necessary to maintain the demonstrated microbial-control outcome through the intended shelf life.⁴
4. Scientific basis for these additions
¹ Product-specific validation: HPP efficacy is matrix-dependent. Fat, water activity, pH, temperature and other characteristics affect microbial inactivation. Niño Fuerte’s work under Dr. Danao specifically demonstrated that fat concentration can influence HPP efficacy.
² Final packaging/post-HPP exposure: In-package treatment prevents environmental recontamination. If the package is opened and the food is ground or formed afterward, HPP can no longer be considered the final environmental pathogen-control step unless that subsequent hazard is independently controlled. This principle is consistent with 21 CFR Part 507 and Dr. Danao’s AAFCO presentation.
³ Formulation-specific efficacy: Equal chamber pressure does not mean equal microbial lethality in products with materially different compositions. Validation therefore needs to apply to the actual formulation or an appropriately demonstrated operating envelope rather than merely to the HPP equipment settings.
⁴ Post-process time and temperature: HPP can cause sublethal microbial injury rather than immediate absolute destruction. Recovery can depend upon the organism, food matrix, subsequent temperature and storage period. Accordingly, “time” and “temperature” should not be interpreted solely as conditions occurring inside the pressure vessel.
I would also recommend clarifying the responsibility of commercial HPP tolling facilities. Where a toller performs an HPP process intended to function as a microbial preventive control, the toller itself should be responsible for delivering the validated process parameters and communicating the validated boundaries and post-processing requirements to the manufacturer/co-packer/customer. A manufacturer cannot reasonably comply with those boundaries if the toller does not provide them, as the toller is the “expert” for their process and must therefore be liable for its failures if they fail to educate their clients on proper methodology.
A related labeling concern: “raw”
I would also encourage the committee to consider whether HPP’s relationship to the term “raw” needs clarification.
HPP is routinely described as “nonthermal,” but nonthermal does not mean unchanged.
Peer-reviewed reviews describe pressure-induced protein unfolding and structural modification, altered protein functionality and nutritional characteristics, and effects on proteins and lipids, including oxidation under some conditions. At approximately 600 MPa, HPP can cause significant protein denaturation and cooking-like physical effects in meat.
AAFCO’s present concept of “raw” appears principally concerned with whether heat was applied. That creates an unusual result in which a food can undergo substantial pressure-induced changes (which may not “apply” heat, but the process does produce heat up to 97.2°F in some cases) yet remain “raw” because the intervention is categorized as nonthermal.
Nonthermal and raw should not necessarily be treated as synonymous.
I am not suggesting that this question needs to be resolved within the HPP definition itself, but defining HPP presents an appropriate opportunity for AAFCO to examine whether foods subjected to validated pathogen-reduction pressures should instead be identified to consumers as HPP-treated or high-pressure processed, rather than allowing the absence of conventional heat alone to imply an essentially unprocessed food as this does not comply with the current AAFCO definition of raw.
Dr. Mary-Grace Danao would also be an excellent independent technical resource for validating any of these, or other, proposed revisions to the definition:
Mary-Grace Danao, PhD
University of Nebraska-Lincoln
402-472-1595
My goal in raising this is not to discourage HPP. It is the opposite: if AAFCO defines HPP, the definition should distinguish properly validated HPP from simply exposing food to high pressure. Otherwise, the existence of the definition may unintentionally legitimize practices that do not preserve the microbial-control outcome HPP is intended to provide – and that would not represent AAFCO’s intention or create the support and trust from States, industry, and consumers that AAFCO is trying to build.
Thank you for considering it.