As published in Cannabis Science and Technology, Aug 2019
By Dr. Brady P. Carter
Water activity is widely recognized for the safety it provides to food because of its control of microbial growth and it is considered a critical control point for preventing microbial contamination. Water activity provides this same determination of safety in cannabis and consequently is already a part of cannabis regulations in many states. However, at this point, it remains primarily associated with edibles, linking it back to food safety. While water activity is important for the safety of cannabis edibles, it is also important for storage stability of harvested buds and extracts. If cannabis buds are not dried to water activity levels below 0.70 aw, they can support mold growth during storage and transport, leading to the subsequent potential for inhalation of mold spores or mycotoxins. In addition, water activity controls the rate of decarboxylation that can lead to the breakdown of tetrahydrocannabinol (THC). Finally, water activity is correlated to additional critical product quality attributes that are associated with shelf life. In fact, it is possible to predict shelf life based on water activity and to establish an ideal water activity specification for any cannabis or hemp-based products. The objective of this manuscript is to explain the theory and measurement of water activity, explain its mode of action for microbial control, discuss existing water activity regulations for cannabis, and describe additional uses for water activity in the cannabis industry.