Water activity in
Cannabis

Cannabis-based products for both medicinal and recreational use are gaining in popularity and acceptance. However, if not handled properly, these products can pose a safety issue for consumers.

Dried buds, extracted oils, or processed edibles with microbial contamination can result in allergic reactions, respiratory complications, or foodborne illnesses. From a quality standpoint, changes in efficacy and potency due to chemical reactions or structural loss can also result in poor product and lost revenue.

Water activity is utilized as an effective tool in the food and pharmaceutical industries to maximize microbial, chemical, and physical stability. It provides this same safety and control to the cannabis market and it is important that cultivators and processors understand water activity and how to maximize its usefulness. The importance of water activity to the quality and safety of dried Cannabis has resulted in ASTM D8197-18, which establishes 0.55 to 0.65 aw as the ideal water activity range to prevent degradation due to over-drying and prevent microbial growth due to insufficient drying.

Water activity in cannabis and it’s microbial safety

Each microorganism requires a certain water activity to reproduce and grow. Water activity below a microorganism’s minimum growth limit stresses the organism and forces it into dormancy.A microorganism doesn’t care how much water is in its surroundings, but instead requires a certain energy of water to grow.

The water activity level needed for growth by pathogenic bacteria is 0.87 aw while the growth of common spoilage yeasts and molds begins at 0.70 aw, which is known as the practical limit. Dried cannabis flower remains shelf stable and resists the growth of bacteria, mold, and yeast when processed to the ASTM-recommended water activity range of 0.55–0.65 aw.

The most likely mode of failure for Cannabis when its water activity is too high is mold growth. Although molds themselves generally pose little risk when ingested, cannabis users often inhale contaminated products, allowing mold spores to enter the respiratory tract and trigger asthma symptoms or other respiratory complications.

Water activity in cannabis and it’s stability

Cannabis biomass and edibles at water activities less than 0.70 aw, while not susceptible to microbial spoilage, do not have unlimited shelf life. Instead of microbial growth, the most likely mode of failure for cannabis biomass or edibles in the 0.55-0.65 aw range is chemical degradation. Chemical reactions can affect the chemical composition, taste, appearance, and nutritional value of biomass or edibles. Water activity changes result in changes in reaction rates because of its impact on activation energy, mobility, and the rate constant. Water activity also impacts biomass integrity.

Trichomes begin to lose structure at water activities less than 0.55 aw due to the loss of protective water shells. Drying cannabis below 0.55 aw causes desirable volatile terpenes to evaporate, reducing aroma and quality. It also increases brittleness, making stalk breakage and structural damage more likely. Processing cannabis to its ideal water activity maximizes shelf life by preventing microbial growth while minimizing chemical degradation and preserving product structure.

Water activity in cannabis and storage safety / stability

Because water activity directly affects product stability, cultivators and processors must reduce harvested cannabis biomass to below 0.70 aw and keep it at that level throughout transport and storage. Proper handling prevents water activity from rising to unsafe levels that promote microbial growth or falling too low, which can lead to the loss of valuable terpenes and cannabinoids. High-quality moisture-barrier packaging helps maintain stable water activity under changing storage conditions, preserving product quality and extending shelf life.If you want to learn more about maximizing shelf life through water activity control, feel free to contact us and our world leading experts will advise you.

“Water activity plays a key role in ensuring the safety of cannabis products and maximizing shelf life. Water activity may be a new concept to many in the cannabis industry, and those familiar with water activity may only know of its ability to control microbial growth. However, in many cases, microbial spoilage is not the most likely mode of failure for the shelf life of cannabis products. Water activity is related to all common modes of failure and consequently may be the most important test that can be run on everything from harvested biomass to edibles.”

Dr. Brady Carter
World-renowned specialist in water activity