URL: https://postharvestreport.com/glossary/water-activity
A measure of unbound moisture available to support microbial growth. ASTM D8197-22 specifies 0.55–0.65 aw for dry cannabis flower.
Glossary
Water activity (aw) measures the unbound moisture in cannabis flower that is available to support microbial growth. ASTM D8197-22 specifies an acceptable range of 0.55 to 0.65 aw for dry cannabis flower.
Water activity, not moisture content, is the number that predicts microbial risk and shelf stability. Operators who anchor drying and curing on aw — measured, not estimated — protect quality and pass compliance testing more consistently.
We dispute the 0.65 upper limit and recommend against following it. From extensive experience and testing, anything above 0.60 aw for dense flower can cause a funk odor. The conservative operating line for premium flower is below 0.60.