The drying process for cannabis is essential and delicate. Over drying can destroy trichomes and hurt profits. Under drying can lead to mold, sick customers, and a damaged reputation. With a tight moisture target to hit for an optimal product, understanding the effects of moisture content, relative humidity, and water activity is essential. Read on to learn which moisture process has the most significant impact on quality and consistency.
Preventing Microbial Growth
Preventing mold and other microbial growth in cannabis is essential to quality assurance. While many molds will not make healthy individuals sick, inhaling molds spores can cause fungal infections in the lungs and be particularly dangerous for immunocompromised consumers – many of whom use cannabis for treatment.
The key to preventing microbial growth is understanding and managing water activity. Each organism has a critical water activity level where it will not grow. Therefore, maintaining a suitable water activity prevents microbial growth, keeps the product safe, and is essential to government guideline compliance.
Although it is tempting to use moisture content as a primary moisture measurement, this should be avoided. Moisture content is a less accurate moisture measurement for cannabis because there is no industry standard for what is "dry." With cannabis, the weight loss in the heating and drying process is not only water but also terpenes and flavonoids.
Moisture content, however, does have its place in moisture measurement. The relationship between water activity and moisture content is shown through a moisture sorption isotherm which indicates that small changes in moisture content cause significant changes in water activity. Using the moisture sorption isotherm will give you a very accurate and specific moisture measurement of how moisture will affect your product.
It is also important to remember that water activity is temperature-dependent and that, generally, higher temperatures lead to higher water activity. Higher temperatures also lead to increased rates of decarboxylation. With this in mind, it's wise to give yourself a little leeway in the product's water activity level and relative humidity in case it experiences temperature abuse after packaging.