Water Activity 101

Crop steering offers a framework that gives commercial cannabis cultivators greater control over plant growth and product consistency. And in order to crop steer plants effectively, growers need to be able to track and monitor water activity.

What is water activity?

Water activity is all about energy. The food industry’s water activity definition speaks to the ratio of the vapor pressure of water in a material to the vapor pressure of pure water at the same temperature. In cannabis, water activity is another way of speaking to the internal relative humidity (RH) of the air pockets inside the flower as matching the water activity in the plant material itself.

As water moves from high pressure to low pressure to achieve equilibrium within its environment, using water activity (aw) to measure that movement gives growers insights into their plants’ RH percentage - and understanding RH is the key to knowing how to dry marijuana properly.

While it’s common for operators to focus more on preventing mold and other issues that stem from cannabis that is under-dry, the fact that overdrying can compromise trichome health and quality overall often gets overlooked. Water activity that’s too high can cause fungus, yeast, and microbial growth - and if discovered during the required lab testing process, can result in costly recalls for licensed operators. Low water activity leads to lost terpenes and cannabinoids, and it's often the consumer who discovers it by way of dry, dusty buds and an abundance of kief at the bottom of the package.

Both roads lead to lost revenue for your business.

So when it comes to product quality and potency, monitoring water activity enables growers to reach moisture levels that are just right: not so wet as to allow mold and microbial growth, but not overdried to the point of losing quality - not to mention, profits.

Using sensors to monitor water activity

When dried in low humidity, cannabis buds experience greater variations between them. Drying too quickly can inhibit moisture and cause a crust to form on the buds. To keep from over-and under-drying their cannabis, cultivators must maintain optimal humidity levels in their grow rooms - but the naked eye can only tell so much.

Moisture levels between 0.55 and 0.62 mark the sweet spot on the cannabis water activity scale. To ensure RH is always on point in a grow room, drying room, or curing room, a vapor pressure sensor like ATMOS 14 can help cultivators track and monitor humidity as well as vapor pressure deficit, temperature, airflow inconsistencies, and other factors impacting the overall environment. And when it comes to testing the water activity inside the buds themselves, a chilled mirror dew point sensor like the AQUALAB 3 delivers accurate moisture content readings within one minute.

When used in combination with a cannabis production platform like AROYA, cultivators get a complete picture of what’s going on with their environment, the substrate, and the plants themselves. And growers who crop steer using a controlled approach to water activity will discover firsthand that the process not only preserves safety and quality - it also helps improve the company’s bottom line.

For a deeper dive into water activity and cannabis, check out our webinar.

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