Quick facts
- Water activity measures the amount of available water in food.
- A water activity of 0.85 or less is considered a low-moisture food.
The Minnesota Cottage Food Law requires that cottage food products have a water activity of 0.85 or lower or a pH of 4.6 or lower.
- The Elitech GSP-6 is an affordable way to measure water activity in the home kitchen.
Water activity measures the amount of available water in a food, on a scale from zero to one.
A value of zero indicates no available water.
A value of one indicates pure water.
This is important for food safety because foods with high water activity have enough water available for foodborne illness-causing microorganisms (pathogens) to grow.
Foods with low water activity limit or “starve” pathogens of the water they need. Foods with a water activity of 0.85 or lower have sufficiently low water activity to prevent the growth of most pathogens.
Water activity requirements in Minnesota
The Minnesota Cottage Food Law requires that cottage food products have a water activity of 0.85 or lower or a pH of 4.6 or lower.
Extension YouTube
Testing water activity video series
Water activity is used to determine the safety of cottage foods. Understanding water activity can help cottage foods producers develop and select recipes, pass inspections, and keep customers safe. This video series explores water activity, how to use the Elitech kit, and more.
The Elitech water activity test kit
Water activity meters can be very costly, typically costing thousands of dollars. The Ubbink Lab at the University of Minnesota created an alternative tool called the Elitech GSP-6.
Elitech offers an affordable way for cottage food producers to measure water activity in their products.
Elitech is not a water activity meter, instead it converts the relative humidity of a food sample in an enclosed container to a water activity value. When the relative humidity of a sealed container needs to be 85% or less, this can be converted to a water activity of 0.85.
The Elitech GSP-6 included in kits sold beginning in September 2025 has an orange cap on the probe. Remove the orange cap before using the probe to calibrate or test water activity.
Elitech kits available for Minnesota cottage food producers
The Minnesota Farmers Market Association offers the Elitech GSP-6 PRO Full Kit at cost to registered cottage food producers.
Watch and learn
This short video from Extension introduces what's included in the Elitech water activity test kit and how to use it in your home kitchen.
The Elitech water activity test kit cannot be calibrated directly like most pH meters.
Instead, an Excel Correction Tool is used to calibrate and calculate a corrected value. Instruction for calibration and using the Excel Correction Tool will come with your water activity test kit.
The calibration process takes 30 hours, with a lot of waiting time (5 readings per standard x 4 standards x 1.5 hours each).
Readings can be completed over several days.
Each Elitech device needs to be calibrated individually.
This process should be repeated annually with a new set of water activity standards.
Watch and learn
This short video explains how to calibrate the Elitech water activity test kit and use the Excel Correction Tool.
Once the calibration process is complete, you are ready to test your food samples.
For the most accurate results:
- Test samples from different parts of the product, ensuring to include samples from the most moist part of the food (typically from the very center).
- Test samples at room temperature.
Testing foods for water activity
- Start with a clean and dry food sample jar.
- Prepare a sample large enough to fill the sample jar, without touching the probes when the lid is secured.
- Place the food sample in the bottom of the sample jar.
- Secure the lid with the probes, ensuring the probes are not touching the food sample.
- Allow the sample to sit for at least 2 hours.
- After 2 hours, turn on the Elitech meter and record the relative humidity reading shown in the center display.
- Convert the relative humidity percentage to water activity by moving the decimal two places left.
- Example: 84.3% = 0.843 water activity
- Complete at least 3 water activity tests, each with a new sample from the same batch (5 tests are recommended).
- Calculate the average water activity
- Average = (sum of measurements) ÷ (number of measurements)
Watch and learn
This short video explainins how to test the water activity of your foods at home.
Foods with a hard crust
For breads and similar baked goods, test samples that include both the crust and the interior crumb. The center often has higher water activity because moisture can become trapped during baking.
Foods with multiple components
For products assembled after baking, such as frosted cookies, cakes, or filled pastries, test each component separately. Each component must independently meet cottage food safety requirements.
Instruction for calibration and using the Excel Correction Tool will come with your water activity test kit.
Using the provided spreadsheet, enter the average water activity of your food product in the yellow box to the right of “Measured aw”. The corrected water activity value will automatically calculate to the right of “Actual aw.”
If the product’s water activity corrected value is above 0.85, recipe and/ or process adjustments are needed.
To lower the water activity, consider:
- Increasing bake time
- Increasing sugar
- Decreasing water/ liquids
- Reducing product thickness
How to lower water activity
- Physically remove water by
- drying or dehydrating
- freeze-drying
- cooking
- Add ingredients that bind to water molecules
- Sugar
- Salt
Disclaimer
No liability is assumed by the creators for the reliability of the Excel tool. These materials are for use by producers in developing products, and results are indicative only and aimed to provide directional information when developing recipes. It is strongly recommended to have final recipes tested by certified laboratories.
Reviewed in 2026