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A low moisture content does not necessarily mean that a food product is microbiologically stable. Food safety and stability depend not only on the total amount of water present but also on how much of that water is available for microbial growth.
In this context, water activity (aw) is an important parameter for assessing a food product’s susceptibility to microbial growth, physical properties, and changes during storage.
Particularly in dried foods, confectionery, bakery products, meat products, and concentrated foods, evaluating moisture content together with water activity provides more comprehensive technical information for quality control and shelf-life studies.
What Is the Difference Between Moisture Content and Water Activity?
Moisture content analysis determines the total amount of water present in a food product. Water activity, on the other hand, is a measure related to the availability of water within the product and its equilibrium vapor pressure.
In other words:
Since sugar, salt, proteins, and other components interact with water differently, two food products with similar moisture contents may have significantly different water activity values.
Therefore, total moisture content alone may not always be sufficient to explain a product’s behavior during storage.
How Does Water Activity Affect Microbiological Stability?
Bacteria, yeasts, and molds require sufficient available water to grow, in addition to suitable temperature, nutrients, and pH conditions.
Reducing water activity can limit the growth potential of many microorganisms. However, the minimum aw values required for growth vary among different microbial groups.
For example, certain yeasts and molds can continue growing under low-water-activity conditions that inhibit the growth of many bacteria.
Therefore, a single water activity measurement is not sufficient to establish that a product is safe from all microorganisms.
Low water activity can restrict microbial growth, but it does not necessarily mean that microorganisms or spores already present in the product have been eliminated.
In food safety assessments, aw values should be evaluated together with pH, temperature, packaging conditions, and, where necessary, microbiological test results.
How Can Formulation Changes Affect Shelf Life?
Even minor modifications to a food formulation can alter how water interacts with other ingredients, consequently affecting water activity.
In particular, the proportions of sugar, salt, humectants, and similar ingredients, as well as manufacturing processes such as drying or concentration, can influence this parameter.
For example, two cake or confectionery formulations with comparable moisture contents may exhibit different aw values. These differences can affect susceptibility to microbial growth, texture, and storage behavior.
Water activity measurements can also help assess quality changes associated with moisture migration, such as softening, hardening, or loss of crispness.
Therefore, monitoring water activity during product development, reformulation, and shelf-life studies provides valuable technical information about the effects of formulation changes on product stability.
Nevertheless, determining a product’s actual shelf life requires more than a single analytical result. Appropriate stability studies and, where necessary, microbiological assessments should also be considered.
How Is Water Activity Measured?
During water activity testing, a representative sample is placed in a suitable sample container and introduced into the instrument’s measurement chamber.
Under controlled temperature conditions, the sample is allowed to reach moisture equilibrium with the surrounding air. The instrument then determines the aw value based on the equilibrium conditions.
Water activity is a dimensionless quantity expressed on a scale from 0 to 1. Pure water has an aw value of approximately 1.00.
For example, an aw value of 0.75 corresponds to an equilibrium relative humidity of approximately 75% at the measurement temperature.
Temperature control, proper sample preparation, and standardized measurement conditions are essential for obtaining reliable results.
Which Food Products Require Water Activity Analysis?
Water activity testing supports quality control and stability assessments across various food categories.
Key applications include:
For suitable product categories, combining moisture content analysis with aw measurements provides manufacturers with more comprehensive quality data.
Are There Legal Limits for Water Activity in Foods?
There is no single universal water activity limit applicable to all food categories.
Relevant requirements may vary depending on the product type, manufacturing process, applicable regulations, and the microorganisms being evaluated.
Therefore, the interpretation of analytical results should consider product-specific technical criteria and relevant food legislation.
Although water activity is an important control parameter in food safety management, it does not independently guarantee regulatory compliance or product shelf life.
Water Activity Testing at Bilim Laboratories
At Bilim Laboratories, we perform water activity determination in food products using a validated laboratory method developed with reference to TS 7474 and AQUALAB application principles.
Through this analysis, we provide manufacturers with valuable analytical data to support:
Evaluating water activity alongside moisture content and other quality parameters contributes to a better understanding of product behavior during storage.
For more information about water activity testing, sample requirements, turnaround times, or to request a quotation, please contact Bilim Laboratories.
