Water Activity (Aw)

A measure of the free water available in a product or ingredient, expressed on a scale of 0 to 1 (where 1.0 = pure water). Low water activity (typically below 0.6) inhibits microbial growth, making it an important parameter in ingredient storage and food product shelf-life assessment. Most dry powdered ingredients (including amino acids, protein powders, and food additives) have very low Aw values, which is one reason they have long shelf lives when stored under appropriate dry conditions. When bulk powdered ingredients absorb moisture from the environment (particularly hygroscopic ingredients), Aw increases, creating conditions that can support microbial growth.