WATER ACTIVITY IN DRIED AND CURED MEAT: SAFETY, SHELF LIFE, TEXTURE AND YIELD

For manufacturers of jerky, salami, pepperoni, meat sticks, dried sausages and other shelf-stable meat products, controlling water is essential. But moisture content alone does not tell you whether a product is microbiologically stable.

The more relevant parameter is water activity (a_w).

Water activity measures how available water is for microbial growth, chemical reactions and physical changes. It can therefore help meat processors determine whether a product has reached the required drying endpoint, maintain consistent texture, control shelf life and avoid unnecessary overdrying. In practice, water activity helps answer four important questions:

• Is the product microbiologically stable?
• Has the correct drying endpoint been reached?
• Will the product maintain the intended texture and shelf life?
• Are we removing more water — and therefore more sellable weight — than necessary?

For dried and cured meat, the goal should not simply be to achieve the lowest possible water activity. The goal is to determine the right water activity range for the product and consistently produce within it.

Why water activity matters in dried and cured meat

Drying, curing, salting, fermentation and smoking have been used to preserve meat for centuries. Although early producers did not understand the thermodynamics behind these processes, many traditional preservation methods worked for the same fundamental reason: They reduced the availability of water.

Today, water activity allows us to quantify this effect. This makes a_w much more than a final QC number. Used correctly, it connects:

Food safety → process control → texture → shelf life → production yield

That is why water activity is one of the most useful parameters for understanding and controlling shelf-stable meat products.

What is water activity?

Water activity describes the energy state or availability of water in a product.

It is defined as:

a_w = p / p₀

where:

• p = vapor pressure of water above the product
• p₀ = vapor pressure of pure water at the same temperature

Water activity ranges from 0 to 1.
Pure water has a water activity close to: a_w = 1.00

Water activity can also be related to equilibrium relative humidity:

ERH (%) = a_w × 100

A product at 0.75 a_w, for example, will tend toward equilibrium with an atmosphere of approximately 75% relative humidity at the same temperature. But the real scientific significance of water activity goes deeper than relative humidity.

The science behind water activity: Gibbs free energy and chemical potential

Water activity is a thermodynamic property. The chemical potential of water — its partial molar Gibbs free energy — changes depending on how strongly water interacts with the surrounding product matrix.

The relationship can be expressed as:

Δμw = RT ln(a_w)

where:

• Δμw = difference in chemical potential of water
• R = universal gas constant
• T = absolute temperature
• a_w = water activity

This relationship explains why water activity is fundamentally different from moisture content. Moisture content measures quantity. Water activity reflects the thermodynamic state of that water.

Water bound or strongly interacting with salts, sugars, proteins and other components does not behave in the same way as freely available water. This is why two products containing the same percentage of moisture can have different water activities — and very different microbial, chemical and physical stability. For food safety and shelf-life decisions, that distinction matters.

Water activity vs. moisture content in meat

One of the most common misunderstandings in dried meat production is assuming that moisture content and water activity provide the same information. They do not.

Moisture content tells you: How much water is present?
Water activity tells you: How available is that water?

The relationship between the two depends on the product formulation and structure. Salt, sugars, proteins, fats, humectants and other ingredients influence how water behaves inside the product.

Two meat products can therefore have:

• similar moisture contents but different water activities, or
• different moisture contents but similar water activities.

This has an important practical consequence. A moisture-content specification that works for one jerky formulation cannot automatically be transferred to another formulation and assumed to provide the same microbial stability. Water activity provides a much more direct connection to the biological availability of water.

Water activity and microbial stability in meat

Microorganisms require available water to grow. When water activity decreases, microorganisms experience increasing osmotic stress and eventually lose the ability to multiply. However, different microorganisms tolerate different water activity levels.

As a general principle:

• most pathogenic bacteria require relatively high a_w
• more tolerant bacteria can grow at somewhat lower a_w
• many yeasts and molds can tolerate lower a_w than bacteria
• specialized osmophilic yeasts and xerophilic molds can tolerate particularly dry environments

At approximately 0.60 a_w and below, microbial proliferation is generally considered unable to occur. This does not mean that all microorganisms die below 0.60 a_w. Survival and growth are different concepts. That distinction is critical.

What water activity is considered safe for jerky?

There is no single universal water activity value that makes every meat product safe under every condition. The appropriate specification depends on factors including:

• product formulation
• pH
• processing method
• packaging
• oxygen availability
• preservatives
• target microorganisms
• storage conditions
• applicable regulations

However, water activity plays an important role in regulatory guidance for shelf-stable meat. For jerky, USDA FSIS guidance recommends targeting a critical limit of 0.85 a_w or lower for products stored under aerobic, oxygen-containing conditions, provided appropriate measures are taken to prevent mold growth.

For products vacuum packaged in oxygen-impervious packaging, creating anaerobic conditions, FSIS guidance allows a critical limit of 0.91 a_w or lower as scientific support under the conditions described in its guidance. These values are based primarily on controlling the growth of Staphylococcus aureus, an organism with relatively high tolerance to reduced water activity.

So the important point is not simply to memorize 0.85 a_w. The important point is to understand why the specification exists and whether it applies to the specific product and packaging system. A manufacturer should establish and validate the appropriate critical limits for its own process.

Water activity controls growth — it does not replace a kill step

This is one of the most important distinctions in dried meat safety: Reducing water activity inhibits microbial growth. It does not necessarily kill microorganisms already present in the product.

Pathogens can survive in low-water-activity environments without being able to reproduce. A product can therefore have a low final water activity while viable microorganisms remain present. For products such as jerky, water activity should consequently be understood as part of the stabilization strategy, not as a substitute for a validated lethality treatment.

The process needs to distinguish between two different objectives:
Lethality: Achieving the required reduction of relevant pathogenic microorganisms.
Stabilization: Creating conditions that prevent surviving microorganisms from growing during subsequent storage.

Heat treatment, fermentation, formulation and other validated interventions may contribute to lethality. Water activity is particularly important for the second objective: maintaining stability after the required lethality has been achieved.

This distinction makes water activity an important component of HACCP and process validation — but not a standalone guarantee of product safety.

Don’t just set a maximum a_w — define an optimum target range

A maximum a_w specification is necessary in many applications. But for manufacturing control, a simple statement such as: a_w must be below 0.85 does not answer the complete production question.

Imagine that the validated upper specification is 0.85 a_w. Should every batch then be dried to 0.70? Probably not. Every additional reduction in water activity may affect:

• product weight
• texture
• processing time
• energy consumption
• production capacity
• profitability

A more useful approach is therefore to define an optimum operating range. The upper side of the range is determined primarily by safety and stability. The lower side is influenced by quality and economics.

Conceptually:

MICROBIAL / STABILITY LIMIT

↓

SAFETY AND PROCESS MARGIN

↓

OPTIMUM WATER ACTIVITY RANGE

↓

TEXTURE / YIELD / QUALITY LIMIT

Water activity as a drying endpoint

Drying time is not necessarily the same as drying endpoint. A process may specify:

• 5 hours at a certain temperature
• a defined weight loss
• a certain internal temperature
• a fixed oven program

These parameters describe the process. They do not directly describe the final thermodynamic state of water in the product. Raw materials and processing conditions vary. Differences can occur in:

• initial moisture
• meat composition
• fat content
• slice thickness
• product dimensions
• marinade uptake
• salt concentration
• sugar concentration
• oven loading
• airflow
• humidity
• temperature

Consequently, the same drying program does not always produce exactly the same final product. Water activity provides an objective way to determine whether the required endpoint has actually been reached.

Overdrying means lost yield

For a dried meat manufacturer, unnecessary drying has a direct economic consequence. Meat products are sold by weight and water contributes to that weight. Once the required water activity has been reached, continuing to remove water can reduce the amount of sellable finished product. Overdrying can therefore cause:

• lower final product weight
• lower yield
• longer drying cycles
• higher energy use
• reduced production throughput
• harder texture
• unnecessary production cost

The objective should be to retain as much water as the validated safety, stability and quality requirements allow. This is where water activity can become a financial process-control parameter rather than simply a laboratory measurement. Consider two production strategies:

Process A

The manufacturer uses a conservative fixed drying time and routinely produces well below the actual a_w target.

Process B

The manufacturer understands the relationship between process conditions and water activity and stops drying within a validated target range.

Both products may meet the microbiological specification. But Process B can potentially retain more sellable product weight while also reducing processing time and energy consumption. Across high production volumes, small improvements in yield can become commercially significant.

The sweet spot: safety, quality and profitability

The optimum water activity is where several requirements overlap.

Too high

Potential consequences include:

• insufficient microbial stability
• shorter shelf life
• softer-than-intended texture
• increased spoilage risk

Too low

Potential consequences include:

• excessive moisture loss
• lower yield
• harder texture
• increased drying cost
• unnecessary processing time

At the optimum target

The manufacturer can achieve:

• required product stability
• consistent sensory quality
• reproducible processing
• optimized product yield

This is why the best water activity specification is rarely simply: “As low as possible.”
It is the value — or more realistically, the validated range — that best balances all relevant failure modes.

Formulation and water activity: drying is only one lever

Water activity can be lowered by removing water. But it can also be lowered by changing how water interacts with the product. Common ingredients such as:

• salt
• sugar
• selected humectants

can reduce water activity without requiring the same degree of physical water removal. This makes formulation an important tool in developing dried and intermediate-moisture meat products. The relationship between formulation, moisture content and water activity can be particularly useful during product development. When appropriate for the product, this can support:

• softer texture
• higher yield
• reduced drying
• shorter process times
• improved sensory properties

Formulation changes must of course be evaluated as part of the complete product-safety and regulatory strategy.

Water activity and texture in jerky and cured meat

Texture is a critical quality attribute in dried meat. Consumers immediately recognize whether jerky is:

• too hard
• too soft
• too dry
• too chewy
• inconsistent from package to package

Water activity is closely linked to the physical state of the product and can therefore be a useful tool for controlling texture. Importantly, there is no single ideal a_w for all dried meat. A soft meat snack will require a different target from a traditional hard jerky or dry sausage. This creates an opportunity during product development. Manufacturers can combine:

sensory testing + texture evaluation + water activity

to determine the a_w range associated with the desired consumer experience. Once this range has been established, a_w becomes an objective production parameter that helps reproduce the same product characteristics batch after batch.

Water activity and shelf life

Microbial growth is only one potential cause of shelf-life failure. Once microbial proliferation has been adequately controlled, other mechanisms can become dominant. For dried and cured meat, these may include:

• lipid oxidation
• flavor deterioration
• color changes
• texture changes
• moisture migration
• packaging-related moisture gain or loss

Water activity influences many of these processes because chemical reaction rates and molecular mobility depend partly on the energy state and mobility of water. However, the relationship between a_w and chemical stability is not always linear. Lower water activity does not automatically mean longer chemical shelf life.

This is particularly relevant for lipid-containing products, where oxidative rancidity may become the dominant quality limitation even when microbial growth is no longer possible.

A robust shelf-life strategy therefore asks: What is most likely to cause this specific product to fail first?

For one product, microbial stability may determine the specification. For another, it may be texture. For another, oxidation. The ideal water activity should be defined with the most relevant failure modes of the specific product in mind.

Water activity and packaging

A product does not stop interacting with its environment once it leaves the dryer. During storage and distribution, water can move:

• between the product and package headspace
• through the packaging material
• between different components of the product

The direction of moisture movement is governed by differences in water activity. Water tends to move from a region of higher a_w toward a region of lower a_w until equilibrium is approached. This is why packaging selection is directly connected to water activity management. If packaging allows excessive water vapor transmission, the product may:

Gain moisture

potentially increasing a_w, softening the product or reducing stability.

or:

Lose moisture

reducing product weight and making texture harder or drier.

The correct packaging system therefore helps maintain the product inside its target water activity range throughout its intended shelf life. Water activity should consequently be considered not only during production but also during packaging development and shelf-life validation.

Water activity, temperature and storage conditions

Water activity is temperature dependent. Changes in temperature can alter the interaction between water and the product matrix, and environmental temperature and humidity influence moisture transfer through packaging. This becomes especially important when products are distributed through changing climates. A shelf-stable meat product may experience very different conditions during:

• manufacturing
• warehousing
• sea freight
• road transport
• retail storage

Shelf-life studies should therefore reflect reasonably expected storage and distribution conditions rather than evaluating the product only immediately after production. Water activity provides a useful parameter for tracking whether the moisture state of the product remains stable throughout this journey.

From final-product testing to process optimization

Water activity can be used at several levels of manufacturing maturity.

Level 1 — Final QC

Measure the finished product and determine whether it passes or fails the defined specification. This is valuable, but reactive.

Level 2 — Process monitoring

Measure a_w during development and production to understand how the product approaches its target. Now the measurement begins to explain the process.

Level 3 — Process control

Use the relationship between processing conditions and a_w to define a repeatable drying endpoint and identify process drift. The measurement becomes operational.

Level 4 — Process optimization

Use the validated a_w range to investigate whether the process can retain more moisture, reduce drying time, improve yield or maintain more consistent texture without compromising safety or shelf life.

A practical water activity strategy for dried and cured meat

A strong water activity program can be built around six steps.

1. Identify the relevant risks

Determine the microbiological, chemical, physical and sensory failure modes relevant to the product.

2. Establish the required critical limits

Consider applicable regulatory requirements, scientific literature, product formulation, pH, packaging and validated processing conditions.

3. Define a target range — not just a pass/fail limit

Create sufficient process margin while avoiding unnecessarily low a_w values that reduce yield or negatively affect quality.

4. Correlate a_w with the production process

Determine how drying time, temperature, airflow, formulation and raw-material variability affect final water activity.

5. Link a_w to product quality

Evaluate the relationship between water activity and texture, sensory properties and shelf-life performance.

6. Optimize the process

Once safety and quality requirements are validated, determine whether unnecessary drying, energy use and weight loss can be reduced.

Water activity measurement and ISO 18787

Water activity measurement in foods is covered by an international standard. ISO 18787:2017 — Foodstuffs — Determination of water activity establishes basic principles and requirements for determining water activity in food and animal feed. ISO 18787 provides an internationally recognized analytical framework for water activity measurement and reinforces an important principle: a_w is a defined thermodynamic measurement — not an arbitrary moisture index.

For reliable routine measurements, representative sampling, consistent sample preparation and temperature control remain important, particularly for heterogeneous meat products. For detailed measurement procedures and sample-preparation recommendations, see the Novasina Water Activity Sample Preparation Guide.

Water activity in meat: the key takeaway

Water activity can help manufacturers:

• support microbial stability
• establish a scientifically justified drying endpoint
• distinguish moisture content from actual water availability
• improve batch-to-batch consistency
• control texture
• support shelf-life development
• evaluate packaging
• reduce unnecessary overdrying
• improve production yield

Most importantly, water activity makes it possible to move from a purely conservative drying philosophy to a controlled and measurable target. The objective is not to make dried meat as dry as possible. The objective is to produce it as dry as necessary — and no drier than required to achieve the validated safety, quality and shelf-life targets. That is where water activity becomes more than a measurement. It becomes a tool for safer products, better quality and smarter production.

Frequently Asked Questions About Water Activity in Meat

What is water activity in meat?

Water activity (a_w) describes the energy state and availability of water in a meat product. Unlike moisture content, which measures the total amount of water, water activity indicates how available that water is for microbial growth and other physical and chemical processes.

What is a safe water activity for jerky?

There is no universal a_w value that makes every jerky product safe. The required specification depends on formulation, pH, processing, packaging and other hurdles. USDA FSIS guidance recommends a critical water activity limit of 0.85 a_w or lower for jerky stored under aerobic conditions and permits 0.91 a_w or lower for appropriately packaged anaerobic products under the conditions described in its guidance. Manufacturers should validate the limits applicable to their specific product and process.

Why is water activity more useful than moisture content for jerky?

Moisture content measures how much water the product contains. Water activity measures how available that water is. Because salt, sugar, proteins and formulation affect water availability, two products with similar moisture contents can have different water activities and therefore different microbial stability.

Does low water activity kill bacteria?

Not necessarily. Low water activity primarily prevents microorganisms from growing. Some pathogens can survive for extended periods in low-a_w products. Water activity should therefore not be considered a substitute for a validated lethality or kill step.

Why can overdrying jerky reduce profitability?

Dried meat is generally sold by weight. Once the required water activity has been achieved, additional water removal can reduce sellable product weight, increase processing time and energy consumption and create an unnecessarily hard product. A validated a_w target range can therefore help optimize yield.

Can water activity be used as a drying endpoint?

Yes. Water activity can help determine whether a product has reached its required final state instead of relying only on drying time, temperature or weight loss. This is particularly valuable when raw-material or process variation causes batches to dry differently.

How does water activity affect the texture of jerky?

Water activity is related to the physical state and mobility of water in the product. Changes in a_w can therefore influence softness, hardness and chewiness. Product developers can correlate sensory and texture testing with a_w to establish a target range for consistent product quality.

Does lower water activity always mean longer shelf life?

No. Lower a_w reduces the potential for microbial growth, but shelf life can also be limited by oxidation, flavor deterioration, color changes, texture changes or moisture migration. The optimum a_w should therefore be selected based on the most relevant failure mechanisms for the individual product.

Read the scientific application note by Dr. Brady Carter, global water activity expert, for a detailed look at the underlying science and practical implications.

Scientific and Regulatory References

1. ISO 18787:2017. Foodstuffs — Determination of water activity. International Organization for Standardization.
2. USDA Food Safety and Inspection Service. Compliance Guideline for Meat and Poultry Jerky Produced by Small and Very Small Establishments.
3. USDA Food Safety and Inspection Service. Ready-to-Eat Fermented, Salt-Cured, and Dried Products Compliance Guideline.
4. U.S. Food and Drug Administration. Water Activity (a_w) in Foods.
5. Scott, W.J. Fundamental work on the relationship between water activity and microbial growth in foods.
6. Beuchat, L.R. Research on microbial stability and water activity.
7. Labuza, T.P. Research on water activity, moisture sorption and physical and chemical stability of foods.
8. Leistner, L. Scientific work on hurdle technology and the combined use of intrinsic and extrinsic factors in food preservation.