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. If a microorganism encounters a water activity lower than its required growth limit, it will be stressed and become dormant. 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 processed to the ASTM recommended water activity range of 0.55 to 0.65 aw is considered shelf stable and will not support the growth of bacteria, mold or yeast.

The most likely mode of failure for Cannabis when its water activity is too high is mold growth. While molds themselves are not particularly dangerous if consumed, mold spores present a particular concern for Cannabis products since they are often inhaled, resulting in mold spores in the respiratory tract which can lead to asthma symptoms.

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 in Cannabis. Trichomes begin to lose structure at water activities less than 0.55 aw due to the loss of protective water shells. Consequently, desirable volatile terpenes are lost through evaporation. In addition, stalk breakage and structural loss are more likely in biomass dried to lower than 0.55 aw due to an increase in brittleness. The shelf-life of cannabis products is maximized when they are processed to the ideal water activity that prevents microbial growth while minimizing chemical degradation and structural loss.

Water activity in cannabis and storage safety / stability

Due to its impact on stability, harvested biomass must not only be processed to be to be below 0.70 aw but must remain that low during transport and storage. This means that water activity control begins with cultivators and processors and then must be maintained by transportation and handling to both prevent an increase in water activity to unsafe levels, as well as a reduction in water activity that could lead to the undesirable loss of terpenes and cannabinoids. To prevent water activity changes under varying storage conditions, Cannabis products need to be packaged in good moisture barrier packaging. 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.