What is water activity (aw)?

Water activity (aw) is the ratio of water vapor pressure in a product to that of pure water at the same temperature. It is the controlling parameter for microbial growth, chemical stability, and shelf life. The FDA and USDA use aw limits to define food safety categories (e.g., shelf-stable foods require aw < 0.85).

How is moisture content different from water activity?

Moisture content measures total water as a percent of product weight. Water activity measures only the "free" water available for microbial growth and chemical reactions. A food can have high moisture but low water activity (and vice versa). Both metrics are typically required for product development and regulatory filing.

What methods do you use?

AATLS performs moisture content by Karl Fischer titration (AOAC 925.09) and loss-on-drying per USP/AOAC methods. Water activity is measured on calibrated aw meters (chilled-mirror dew-point or capacitance). Both methods are ISO/IEC 17025 accredited.

Standard turnaround is 2-5 business days from sample receipt. Rush analysis (24-hour) is available for urgent product-release or outbreak investigation testing.

Who typically orders this testing?

Food manufacturers (for HACCP/FSMA compliance and shelf-life validation), cosmetic companies (for preservative efficacy and microbial stability), supplement/nutraceutical manufacturers, and pharmaceutical firms testing excipients and finished products.

Moisture Content & Water Activity Analysis

What is the Optimal Moisture Content and Water Activity?
The moisture content of properly cured cannabis flowers should be below 13%. Within the food industry, water activity below 0.60 aw is considered to be shelf-stable without refrigeration. Products between 0.60-0.85 aw will not require refrigeration but will have a limited shelf-life. Any products above 0.85 will require refrigeration or other way to prevent microbial growth.

Even the smallest amount of water in or on a product can lead to dangerous microbial growth (like bacteria, yeast, and mold) and a spoiled batch of products. Higher moisture content means that products are more susceptible to microbial growth, so testing the moisture content will reveal the probability of any growth occurring (called microbial viability), which ultimately tells us the shelf-life and safety of a given flower or product. Alternative to high moisture content, moisture content that is too low can negatively alter the properties of your products as well, such as how they taste or their texture. It’s important to understand this ratio and where your products fall on the spectrum (see note below).

Water activity measures how microbes will react to any water that exists in your flower or product. Higher water activity indicates higher microbial growth potential, and lower water activity will indicate a lower growth potential, and thus, a longer, more stable shelf-life.

OUR TESTING METHOD!
A moisture analyzer is used to calculate the moisture content, while a water activity meter is used to measure water activity.

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Water activity (Aw) and moisture content testing for food safety and shelf-life validation.

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Moisture & Water Activity — 2026 Food Safety Update

Reviewed for accuracy: June 2026. FSMA Preventive Controls and the FDA Food Traceability Rule continue to drive moisture and water activity monitoring requirements for shelf-stable foods, ready-to-eat products, and ingredient supply chains in 2026. Water activity (aw) < 0.85 remains the FDA limit separating shelf-stable from potentially hazardous foods.

AATLS performs ISO/IEC 17025 accredited moisture analysis (Karl Fischer titration, loss-on-drying) and water activity measurements on calibrated aw meters. We support food manufacturers, cosmetic companies, supplement/nutraceutical firms, and pharmaceutical QC labs with 2-5 day turnaround and rush 24-hour service.

For shelf-life studies, product reformulation testing, or FDA/USDA compliance batches, call (928) 985-9399 or use the form below.