WATER ACTIVITY IN THE 2026 FDA FOOD CODE: WHAT FOOD BUSINESSES NEED TO KNOW
Water activity has been part of food safety decision-making for decades, but the 2026 FDA Food Code gives it renewed practical relevance, particularly through new guidance for dehydration and freeze-drying. For businesses already measuring aw, the update is a useful reason to review whether the value being measured is actually connected to a scientifically supported endpoint, whether the sample represents the relevant part of the batch, and whether the result is being interpreted correctly in the context of the process.
The FDA released the 2026 Food Code on September 17, 2026. The new edition introduces dedicated Annex 6 guidance for dehydration and freeze-drying, adds new guidance for acidified sushi rice and revises the pH–aw decision tree used when determining whether a food requires time/temperature control for safety. Water activity also appears throughout the Code in several established applications, including food classification, reduced-oxygen packaging, rehydration, refrigerated fish, cold-holding considerations, date marking and HACCP. [1–4]
For food businesses, the important message is not that the new Code suddenly requires every operation to measure water activity. The more useful question is where aw is being used as part of a safety decision and what evidence is needed to support that decision.
First, understand what the FDA Food Code is
The FDA Food Code is a model code intended primarily for the retail and foodservice sector, including restaurants, grocery stores and institutional foodservice operations. FDA provides it for adoption by state, local, tribal, territorial and federal regulatory jurisdictions, so publication of the 2026 edition does not automatically create a new federal aw-testing obligation for every food manufacturer or every food business in the United States. [1,2]
This distinction matters when reading the new water activity guidance. Some sections are codified model provisions, while others are explanatory material in the annexes intended to help regulators and food establishments understand the scientific reasoning behind those provisions. The practical value of the Code is therefore not simply to extract a number such as 0.85 or 0.91 aw and place it into a specification, but to understand why that value appears, what product and process it applies to, and what additional controls are assumed.
What is actually new for water activity in the 2026 edition?
The most significant new material is found in Annex 6, Sections 5 and 6, which introduce dedicated processing guidance for dehydration and freeze-drying. FDA’s official summary of changes confirms that both sections are new in the 2026 edition. The sushi-rice acidification section is also new, while the pH–aw decision tree in Annex 3 has been revised so that the diagram matches the accompanying instructions. [3]
This does not mean that water activity itself is new to the Food Code. The Code has long used aw in determining whether a food is considered time/temperature control for safety, in reduced-oxygen packaging provisions and in the scientific rationale for other food-safety decisions. What has changed is that dehydration and freeze-drying now receive much more explicit practical treatment, including target endpoints, instrument calibration, sampling, process validation and post-drying handling.
Where water activity appears in the 2026 FDA Food Code
The table below summarizes the most practically relevant references to water activity in the 2026 Food Code and explains how aw is used in each context. Some passages define specific criteria, while others provide supporting scientific or operational guidance; the presence of aw in a section should therefore not automatically be interpreted as a requirement to perform an aw measurement in every case. Page numbers refer to the printed pages in the Food Code. [4]
| Application | Where to look | How water activity is used |
|---|---|---|
| Food classification | §1-201.10(B), pp. 19–20; Annex 3, pp. 275–276 | pH–aw tables and a decision tree are used to help determine whether a food is non-TCS or whether further product assessment is required. |
| Dehydration — new guidance | Annex 6, §5(D)(3), p. 568 | Calls for a scientifically supported target aw endpoint for each product, calibrated instruments, defined sampling procedures and sampling that considers worst-case batch conditions. |
| Freeze-drying — new guidance | Annex 6, §6(C)(4), p. 574; §6(E), p. 578 | Calls for scientifically supported aw endpoints and defined sampling. The freeze-drying decision tree recognizes a validated water activity or moisture endpoint when demonstrating shelf stability. |
| Reduced-oxygen packaging | §3-502.12(B)(2), p. 77; Annex 3, p. 411 | aw ≤0.91 is one of several secondary barriers that can be used with refrigeration at ≤5°C/41°F and other required controls. |
| HACCP | Annex 4, pp. 501–502 | Water activity is identified as a possible scientifically based critical-limit parameter and as a measurement that can be used in monitoring. |
| Inspection equipment | Annex 5, p. 522 | A water activity meter is listed among equipment that may be provided to inspectors on an as-needed basis. |
| Rehydration | Annex 3, pp. 388–389 | FDA explains that dehydration reduces aw whereas rehydration increases it again, potentially creating conditions that support microbial growth if time and temperature are not properly controlled. |
| ROP fish | Annex 3, pp. 389–390 | Water activity can form part of an additional barrier to C. botulinum growth. Whether certain frozen ROP fish may be held refrigerated depends in part on whether barriers such as pH or aw are present. |
| Cold holding | Annex 3, p. 396 | Water activity is one of the intrinsic factors, together with temperature and pH, considered in pathogen-growth models used to support refrigerated holding conditions. |
| Hard and semi-soft cheeses | Annex 3, pp. 401–402 | Water activity is listed among several factors that may control Listeria monocytogenes growth and form part of the scientific basis for date-marking exemptions for specified cheeses. |
| Sushi rice — new guidance | Annex 6, §4, pp. 565–566 | The section refers to pH–aw interactions and general HACCP critical-limit principles, although the actual specified acidification control for sushi rice is pH ≤4.2. |
The table shows that water activity does not serve one single regulatory purpose throughout the Code. Depending on the application, it may help classify a food, define a drying endpoint, act as one hurdle within a reduced-oxygen packaging strategy, contribute to microbial-growth modeling or form part of the scientific rationale behind a storage or date-marking decision. [4]
Dehydration: the biggest practical change for aw users
The new dehydration section is probably the most relevant part of the 2026 update for laboratories already working with water activity. FDA describes dehydration as the removal of water to reduce aw and inhibit microbial growth and defines a low-moisture food in this section as a food with aw below 0.85. At the same time, the guidance makes clear that reducing aw does not reliably destroy pathogens and that organisms such as Salmonella may survive for extended periods in low-moisture foods. [4]
This distinction is important because it separates growth control from lethality. A finished product may have an aw low enough to prevent microbial growth while still containing viable organisms introduced through raw ingredients or post-process contamination. The Food Code therefore treats the drying endpoint as one part of the food-safety system rather than as proof that the product has received an effective kill step.
The most important practical wording appears in Annex 6 §5(D)(3). FDA recommends establishing a scientifically supported target aw endpoint for each product, verifying that endpoint using calibrated instruments and defined sampling procedures, and designing the sampling plan to represent worst-case conditions. The Code specifically identifies variability in product thickness, loading density, dryer temperature, airflow and humidity as reasons why aw may vary across a batch. [4]
For a business, this means that a single convenient sample from the easiest part of a dryer may not provide the evidence needed to demonstrate that the entire process has reached its intended endpoint. A more defensible sampling procedure considers where the product is most likely to dry slowly, where the thickest pieces are located or which loading conditions could produce the highest aw.
The Code also emphasizes the rate at which the product reaches the target. During the early stages of drying, the product may remain in an aw and temperature range that still permits microbial growth or toxin formation, so the process must reach the intended endpoint within an appropriately controlled time. FDA specifically notes that staphylococcal enterotoxin formation can occur around aw 0.86–0.87 under favorable conditions, which illustrates why simply measuring the finished product after an uncontrolled drying process is not enough. [4]
A target aw should be product-specific, not copied from another product
The reference to aw <0.85 in the dehydration section can easily be misunderstood as a universal target for every dried food. The Code itself takes a more nuanced approach by asking establishments to establish a scientifically supported endpoint for each product and by recognizing that semi-dried products may remain above 0.85 and therefore still require refrigeration or other TCS controls. [4]
This is an important practical principle. A dried fruit, jerky product, herb, fish product and semi-dried vegetable do not automatically have the same formulation, hazard profile, intended storage conditions or required aw limit. A meaningful specification should therefore be supported by the product’s intended use, relevant hazards and processing conditions rather than simply adopting a familiar number from another category.
Freeze-drying: shelf stability needs to be demonstrated
The new freeze-drying section follows many of the same principles but makes one point particularly clear: freeze-drying itself is not a lethality treatment. FDA notes that pathogens including Salmonella, Listeria monocytogenes and Staphylococcus aureus may survive freezing and freeze-drying with relatively little reduction. [4]
As with dehydration, the guidance calls for a scientifically supported target aw endpoint, calibrated instruments and a defined sampling procedure that considers worst-case variation such as product thickness and loading density. The product also needs protection from condensation, environmental contamination and subsequent moisture uptake after freeze-drying, making packaging and post-process handling part of the stability strategy rather than an afterthought. [4]
The decision tree in Annex 6 is particularly useful because it prevents an overstatement of aw as the only acceptable endpoint. For a freeze-dried product intended to be shelf stable, FDA asks whether a validated water activity or moisture endpoint has been established and verified. If not, the decision tree states that shelf stability cannot be demonstrated. [4]
For laboratories, the practical message is therefore not that aw must replace every moisture-content method. The measurement chosen should be scientifically justified for the product, validated for the intended decision and linked to the actual shelf-stability strategy.
Packaging matters after the drying process is finished
A correct aw measurement at the end of production does not guarantee that the product will remain at that water activity throughout distribution. Both the dehydration and freeze-drying guidance emphasize protection from condensation and moisture uptake during post-process handling and packaging. [4]
This means that aw can also become a useful parameter during shelf-life and packaging validation. If the product leaves the dryer within its validated range but later increases in aw, the investigation should move beyond the drying process and consider packaging barrier performance, seal integrity, handling conditions and environmental exposure.
For quality teams, this creates a useful separation between two questions. The first is whether the process reaches the correct endpoint; the second is whether the packaging and storage system maintain that endpoint for the required period.
Food classification: aw works together with pH and processing history
Water activity also remains central to the Food Code definition of a Time/Temperature Control for Safety food. The Code contains tables that combine pH and aw and distinguish between foods that are non-TCS and foods requiring further product assessment. Which table applies depends partly on whether the food has been heat-treated and whether it was packaged afterwards. [4]
This is an important example of why individual aw values should not be taken out of context. A particular aw can have a different regulatory meaning depending on pH, processing history and packaging. In some products neither pH nor aw alone may provide sufficient control, while their combined effect can prevent microbial growth through what is commonly described as hurdle technology. [4]
The 2026 edition revised the associated Annex 3 decision tree to better match the instructions. The underlying principle remains the same: classification is based on the complete product and process rather than one isolated measurement. [3]
Reduced-oxygen packaging: 0.91 aw has a specific context
The value 0.91 aw appears in the reduced-oxygen packaging provisions and is particularly easy to quote without the surrounding conditions. In §3-502.12(B), aw ≤0.91 is one of several secondary barriers that can be used in conjunction with refrigeration at 5°C/41°F or below and other required ROP controls. [4]
The Food Code explains that C. botulinum will not produce toxin below aw 0.91 and gives a minimum aw of 0.92 for growth of Listeria monocytogenes in this context. The alternative barriers listed include pH ≤4.6, specified cured meat or poultry products and foods with high levels of competing microorganisms. [4]
For a business, the practical point is that 0.91 aw is not a universal room-temperature shelf-stability limit. It appears here as one barrier within a specific reduced-oxygen packaging system that also includes refrigeration and additional process requirements.
ROP fish: water activity can determine whether another barrier exists
The Annex 3 discussion of reduced-oxygen packaged fish illustrates the same principle from another angle. FDA explains that control of nonproteolytic C. botulinum may rely on freezing, refrigeration or refrigeration combined with other barriers such as salt or water activity control. [4]
Where individually packaged frozen ROP fish does not carry a keep-frozen instruction, the suitability of refrigerated storage can depend in part on whether additional barriers such as pH or water activity are present. If those barriers are absent, the Code requires specific handling intended to prevent prolonged refrigerated storage of fish within the reduced-oxygen package. [4]
This is another example where the aw result has meaning only when interpreted together with packaging, temperature and the biological hazard being controlled.
Rehydration: the aw can move in the opposite direction again
The 2026 Food Code also gives more attention to commercially dehydrated foods that are subsequently rehydrated. FDA explains that dehydration reduces aw to inhibit pathogenic growth, while rehydration restores moisture and increases aw, potentially recreating conditions that allow microorganisms to multiply. [4]
This is especially important because a shelf-stable dehydrated product does not necessarily remain non-TCS after water has been added. Manufacturer preparation instructions may therefore include water temperature, soaking time, refrigeration during rehydration, subsequent cooking and post-rehydration holding requirements. FDA recommends following those instructions or using an appropriate hazard-analysis approach when an alternative procedure is proposed. [4]
For food businesses, this means that aw should not be viewed only as a property established once during production. A change in product state, such as rehydration, can change the microbial environment again and therefore change the controls that are required.
Cold holding: aw is one factor, not a stand-alone rule
Water activity also appears in the scientific discussion supporting refrigerated holding conditions. Annex 3 explains that pathogen-growth models used historically in developing holding times allow for variation in temperature, pH and water activity. [4]
This should not be interpreted to mean that a business can simply measure aw and independently determine a new cold-holding time. The reference demonstrates instead that water activity is one of several intrinsic factors that affect microbial growth and that it can be relevant when scientifically evaluating how a food behaves under refrigerated conditions.
The distinction is useful because it prevents the table entry from being overstated. In this section, aw contributes to the scientific basis behind growth modeling rather than functioning as a stand-alone operational limit.
Hard and semi-soft cheeses: aw contributes to the rationale for date-marking exemptions
Another interesting reference appears in the discussion of hard and semi-soft cheeses. FDA explains that certain cheeses manufactured according to the applicable standards of identity are exempt from date marking based on several factors that can control Listeria monocytogenes growth, including organic acids, preservatives, competing microorganisms, pH, water activity and salt concentration. [4]
The important wording here is one of several factors. The Code is not saying that measuring the aw of any cheese automatically creates a date-marking exemption. Instead, water activity forms part of the scientific basis underlying the established exemption for the specified products.
This distinction again illustrates why the Food Code should be read by application rather than as a list of universal aw thresholds.
HACCP: water activity can become a measurable critical limit
Annex 4 describes water activity as one of the scientifically based parameters that may be used to establish a critical limit at a Critical Control Point. It also lists aw among measurements that can be used as part of monitoring activities. [4]
This wording is important because water activity itself is not automatically a CCP. A process step becomes a CCP based on the hazard analysis, and aw may then be selected as the measurable criterion used to distinguish acceptable from unacceptable process conditions.
For a drying operation, for example, the drying step may be identified as a CCP and the validated aw endpoint may become one of its critical limits. In another process, aw may be monitored as verification or supporting process information rather than as the formal critical limit.
The inclusion of aw meters in inspection guidance is also worth noting
Annex 5 lists a water activity meter among equipment that may be provided to inspectors on an as-needed basis, alongside items such as pH meters, sample-collection kits and time/temperature data loggers. [4]
This is not a requirement that every inspector or every food establishment must own an aw meter. It does, however, show that FDA considers water activity measurement sufficiently relevant to retail food-safety investigations that it appears among the tools that regulatory staff may need when assessing specific operations.
For businesses using aw as a safety control, this reinforces the value of having a clearly documented measurement procedure and being able to explain how the measured value relates to the process decision.
What should an aw user review after the 2026 update?
A useful review does not need to begin by changing every SOP. Start with one product for which water activity influences shelf stability, TCS classification, drying or another food-safety decision, and trace the logic from the specification back to the process.
The team should be able to explain why the aw limit was selected, which evidence supports it and whether another condition such as pH, refrigeration or packaging is part of that conclusion. For drying and freeze-drying processes, the sampling procedure should also show how the operation accounts for the parts of the batch most likely to retain the highest water activity.
The instrument and measurement procedure should be part of the same review. Annex 6 specifically calls for calibrated instruments and defined sampling procedures when verifying dehydration and freeze-drying endpoints, so the laboratory should be able to demonstrate that instrument performance is controlled and that operators follow a consistent measurement procedure. [4]
The final step is to review what happens after a failing result. A validated endpoint is only useful if the SOP also defines whether the product is reprocessed, held for evaluation or prevented from entering commerce when the requirement is not achieved. FDA’s new Annex 6 guidance explicitly addresses disposition of nonconforming dehydrated and freeze-dried products, making corrective-action planning part of the process rather than something decided only after a deviation occurs. [4]
The practical takeaway from the 2026 Food Code
The strongest message for water activity users is not that FDA has introduced one new aw limit. The 2026 Food Code shows something much more useful: water activity is applied differently depending on the food-safety question being asked.
In dehydration and freeze-drying, aw can define and verify a process endpoint. In TCS classification, it works together with pH and processing history. In reduced-oxygen packaging, it can provide one of several microbial barriers. During rehydration, increasing aw can recreate conditions favorable to microbial growth, while in refrigerated products and certain cheeses, aw can form part of the scientific reasoning behind storage and date-marking decisions.
For food businesses already measuring water activity, the 2026 update is therefore a good opportunity to move beyond asking whether an aw value “passes”. The more useful questions are whether the limit is scientifically justified, whether the sample represents the relevant product condition, whether the measurement method is controlled and whether the result is being interpreted within the correct process and regulatory context.
That is ultimately where water activity becomes most valuable: not as an isolated laboratory number, but as a parameter linked to a clear food-safety decision.
Sources
[1] U.S. Food and Drug Administration. The FDA Releases 2026 Food Code. September 17, 2026. Official release announcement and overview of the new edition
[2] U.S. Food and Drug Administration. Food Code 2026. FDA overview explaining the purpose of the Food Code and its role as a model for adoption by regulatory jurisdictions
[3] U.S. Food and Drug Administration. Summary of Changes in the 2026 FDA Food Code. Official summary identifying the new dehydration, freeze-drying and sushi-rice guidance and revisions to the pH–aw decision tree
[4] U.S. Food and Drug Administration. FDA Food Code 2026. Primary source for the section, page and technical references discussed throughout this article
