Water Activity Test
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Price
$50 per analysis
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Turnaround time 7 – 9 Business Days
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Rush Available
Technical data sheet
Print- Method description
Water activity measurement determines the amount of free, unbound water that is available for microbial growth or moisture equilibration and migration. Water activity is a ratio between the water vapor pressure of the sample and the vapor pressure of pure water under the same conditions.
Medallion uses two different measurement techniques for water activity analysis: the Chilled Mirror Dewpoint sensor and the Tunable Diode Laser sensor.
For Chilled Mirror Dewpoint, the sample is sealed in the instrument chamber and allowed to equilibrate to chamber temperature and the unbound water from the sample equilibrates in the headspace. The instrument cycles the temperature of the mirror to determine the temperature at which the water vapor in the sample headspace condense on the mirror. The dewpoint temperature and relationship to the relative humidity is a fundamental correlative property water vapor.For Tunable Diode Laser, the sample is sealed in the instrument chamber and allowed to equilibrate to chamber temperature and the unbound water from the sample equilibrates in the headspace. The instrument sends a narrow band light beam through the headspace of the sample chamber and determines the amount of incident light absorbed by the water molecules in the headspace. The amount of absorbed light is proportional to the amount of water vapor equilibrated in the headspace.
The Tunable Diode Laser instrument is more appropriate for samples that contain volatile oils, ethanol, propylene glycol, or other volatiles that are likely to interfere with the chilled mirror dewpoint technique.
- Acceptable matrices
Foods and food ingredients
Please indicate if sample contains any of the following:
Allspice, Basil, Black Pepper, Cayenne Pepper, Chili Powder, Cinnamon, Cloves, Coriander, Cumin, Garlic, Ginger, Glycerin, Nutmeg, Oregano, Paprika, Sage, Acetic Acid, Ethanol, Isopropanol, Propylene Glycol, Lactic Acid (>10%), Essential oils (Cinnamon, Clove, Lemon, Peppermint, Rosemary, or similar), Coffee, Tea, Chicory Drink or Chicory Root extracts.
Samples that contain these ingredients will be analyzed with the Tunable Diode Laser.
- Unacceptable matrices
Cosmetics, non food samples
- Limit of quantitation
0.250 aw units
- Equipment
Water Activity Meter
- Method reference
AOAC 978.18, AOAC 2021.04
- 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
The correlation between moisture content and water activity for a specific sample is known as a moisture isotherm. It is possible to have samples with relatively high water content and lower water activity if the water is well bound within the sample matrix. Conversely, it is also possible to have a low moisture content sample with a relatively high water activity. Water activity analysis provides a means of assessing the storability and bacterial susceptibility of shelf-stable foods. Different microorganisms cannot survive below certain water activity levels. Examples of critical water activity levels include: botuli at <0.93; bacteria at <0.86; yeast cells at <0.78, and mold spores at <0.65.
Common Water Activity Test Testing Questions
Water Activity can provide critical information into how likely microbial growth is, and what kinds of microbes may be present (yeast/mold, bacteria etc.).
Water Activity and Moisture have little, if any, correlation to each other. Water Activity is a measure of the free and unbound water content in the sample while a Moisture value is the overall water content. Most often, water needs to be available and accessible to microbes to allow for growth. A lower Water Activity is an indicator that despite the moisture content, the water may be bound and not accessible to microbes to grow.
This can depend on your intended storage conditions (refrigerated vs. ambient etc.), type of packaging, and product. We recommend that all of our clients assessing the shelf life of their products consult with food safety and regulatory experts to ensure that all testing plans and results comply with guidelines.
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.
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.
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