CARO’s Water Activity Method for Cannabis Testing

Posted on March 22, 2022

Spoiler alert: this post is NOT about water skiing.

In the scientific world, water activity (a_w) is an indicator of the shelf life or stability of a food product.  Water activity finds relevance to cannabis producers as it provides a metric for the likelihood of bacteria growth in your cannabis infused edible products.  The water activity procedure is based on a Health Canada method that CARO has used for years with various non-cannabis food products and is transferable to many variations of cannabis products.

Scientifically speaking, the water activity of a food is the ratio between the vapor pressure of the food itself (when in a completely undisturbed balance with the surrounding air media), and the vapor pressure of distilled water under identical conditions.  In more simple terms, it is the fraction of the water in the product that is not bound to your product, and therefore available to microorganisms to use as they please (and there is nothing they like more than growing!)  Water activity is reported on a scale of 0 to 1.0 – the lower the water activity ratio, the less hospitable your product is for microbial growth.  The table below, borrowed from the Government of Manitoba’s Website, provides a snapshot of the water activity ratios that allow for the growth of some of the more common food-related microorganisms:

So How Does it Work?

Here is a quick break down of CARO’s water activity method in cannabis-based products:

 1. Detecting water activity is actually much simpler than some of CARO’s other methods. To begin, the analyst will calibrate and verify the instrument following proper QA/QC protocols.

2. Secondly, the analysist will ‘prepare’ the sample by spreading it onto a small water activity dish.

3. Lastly, the analysist will insert the sample dish into the detecting instrument.

4. Wait a few minutes for the sample to get a stable reading (this is done in duplicate per sample).

How the Method is Validated

CARO’s water activity method is validated through a precision and accuracy study. For cannabis specifically, the analyst performs 10 replicates of a matrix or sample.  They will also further verify infused matrices by performing replicates with baked goods, gummies, and chocolates, to make sure the presence of THC/CBD doesn’t cause any issues with getting a water activity reading (we would call these issues “matrix interferences”).

CARO is always researching new methods and applying the most appropriate methods to help you reach your testing objectives.  Our capabilities across a variety of cannabis matrices will provide you with the information you need about your product, so you can be confident that your product is safe as you move into the next steps of production. If you have questions about where to start and what testing to consider for your unique matrix you can go to our client resources page (scroll down to find the Cannabis resources), or reach out to us directly through [email protected].