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Water Activity Test

  • Price

    $50 per analysis

  • Turnaround time

    7 - 9 Business Days

  • Rush


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Water Activity Test

Technical data sheet


Method description

This method is a measurement relating to the free, unbound water present in food and food products. The atmosphere of a special sampling cell is evacuated, repressurized, and measured manometrically. The results are correlated to water activity in the sample.

Acceptable matrices

Foods and food ingredients

Unacceptable matrices

Cosmetics, non food samples, and samples containing high levels propylene glycol

Limit of quantitation

0.250 aw units


Water Activity Meter

Method reference

AOAC 978.18

Reportable unit

aw Units. Water activity (aw) is the ratio of the vapor pressure of the water in the sample to the vapor pressure of pure water at the same temperature.

Sample size requirements

25 g

Information required by submitter

Please supply estimates

Additional information

Water activity has little, if any, relationship to the total moisture content of the food. Water activity does provide a means of assessing the storability and bacterial susceptibility of shelf-stable foods. It is known that microorganisms cannot survive below certain aw levels, depending on the type of microorganism with botuli at <0.93; bacteria at <0.86; yeast cells at <0.78, and mold spores at <0.65.

*Prices and offerings are subject to change without notice.

Common Water Activity Test Testing Questions

The water activity of a food is the ratio between the vapor pressure of the food itself and the vapor pressure of pure water at the same temperature. It represents the amount of available moisture in a product.

There is no microbial proliferation below a water activity of 0.6.

Water activity is used as a critical control point in HACCP programs. Reducing the water activity of a product can inhibit microbial growth.

While our sales and customer service team are happy to answer general testing questions, consultations typically start at a rate of $250 per 30 minutes regarding the interpretation of reported test results or questions about our test methods. We cannot consult on regulations, tolerance limits, or claims.

We make every effort to keep our methods and detection limits up to date according to the latest standards and qualifications. If you have any questions regarding the limit of detection/quantification or method references, please contact our Customer Service team at 1-800-245-5615.

Our standard turnaround time is 10 business days for most assays. There are some assays that require a longer turnaround time. We also offer a RUSH service that is half the time of the standard turnaround time of the assay at double the cost of the assay. A few assays that we provide cannot be rushed due to the nature of the test. Please check the specific assay you are interested in regarding the ability to RUSH the turnaround time.

Medallion Labs, a division of General Mills, offers multiple areas of expertise for analytical testing and product evaluation for the food and ingredient industry. Our areas of expertise include Chemical Analysis, Nutritional Analysis, Food Safety, Shelf Life Studies, Microbiology, Specialty Fibers, Physical Testing, Allergen Testing, as well as Product Evaluation (which includes Product Performance and Sensory Evaluation) and Technical Consulting/Method Development. Our methods are developed for the testing of food products and ingredients.

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Medallion Labs

A food testing program designed with mid-market and enterprise food and ingredient manufacturers in mind.