Water activity (aw) is particularly critical to food and pharmaceutical safety for predicting the growth of bacteria, yeasts, molds, and more. Products are generally safer to transport and store at lower water activity levels. This also applies to cannabis which is why water activity already features as part of cannabis regulations in legalized markets.

Lower water activity means water in the system behaves less like pure water. The risk in this is having the plant become either:

  • too dry, which will make the trichomes brittle, delicate, and less potent or destroy them completely, and your profits along with them
  • or too wet, which can damage your company’s reputation by causing mold or contamination and exposing customers to health risks.

Water Activity and Storage

To store and transport it, harvested cannabis (marijuana and hemp) must be dry to avoid the development of molds, yeasts, or bacteria which grow during storage if the water activity is too high. Dried biomass generally has water activity ranging from 0.60 to 0.70.  Molds (besides a few rare xerophilic species) stop growth at water activity under 0.65.

Water activity is temperature dependent; generally, higher temperatures lead to increased levels of water activity. Cannabis buds with water activity levels above 0.65 can grow mold during storage and transport, putting users at risk of inhaling mold spores or mycotoxins. Meanwhile, a clear correlation between moisture content causing microbial growth, chemical or physical stability has not been found.

To minimize this risk, we aim for water activity levels below 0.65. Above this level there are also other risks besides mold and bacteria, such as undesired oxidation and possible THC decarboxylation. Therefore, water activity should be monitored across the supply chain, starting with growers.

Shelf Stability

While products with a level higher than 0.70 aw but less than 0.86 aw are considered shelf-stable, pathogenic bacteria cannot grow on the product, but mold and yeast can. These products are not dangerous as molds and yeast do not lead to foodborne illnesses, but even nonpathogenic organisms can cause the production of mycotoxins and aflatoxins, which are potentially harmful to eat and more so to inhale.

To prevent this, water activity should be kept below 0.65 aw or other precautions such as vacuum packing or a preservative system must be implemented.

Many legal cannabis markets have set the water activity limit at 0.65 and new markets opening are likely to do the same.

GemmaCert Tests for Water Activity

GemmaCert’s November over-the-air software update empowers users worldwide to test for water activity so that they can determine if their product is safe for transport and storage. Unlike other solutions on the market, GemmaCert not only enables real-time water activity analysis but also does so for whole flower buds. To determine the water activity for a batch of flowers, the analysis must be conducted on whole flowers rather than ground material; grinding leads to water loss and misrepresentation of the actual water activity level, and wrong decision-making based on such results can have adverse commercial and health ramifications.