Water Activity vs. Moisture Content: Learn The Important Difference
For anyone who wants to ensure the longevity and shelf life of cannabis flower, understanding the amount of water the flower contains is a must. This is because too much water in any agricultural product can lead to microbial contamination.
To that end, most cannabis cultivators and producers have a clear understanding of moisture content, the total amount of water present in any given cannabis product. Some use this term interchangeably with water activity, but there is a world of difference between the two: In short, while moisture content detects the amount of water within a sample, water activity measures the available or “free water” that can feed the growth of mold, mildew, and other contaminants.
Analytical labs serve an important role in testing water activity and moisture content, as well as explaining to clients and consumers alike the important distinctions between them. Although there is plenty of confusion around the difference between moisture content and water activity, measuring both metrics is critical to identifying cannabis flower at risk of microbial contamination.
In this blog, you will learn:
The difference between moisture content and water activity
How water activity and moisture content relate to product quality
How cannabis analytical labs test for moisture content and water activity
New Jersey’s regulations governing water activity and moisture content testing in cannabis
Moisture content vs. water activity: What is the difference?
Moisture content refers to the total amount of water present in the cannabis flower, while water activity measures the availability of water in the flower. Available water can be defined as any water that is not needed for cellular development and function. It is this unused water that could result in higher susceptibility to microbial contamination.
Water activity is a measurement taken by a cannabis testing laboratory to identify water availability and gauge how vulnerable cannabis is to microbial contamination from contaminants like bacteria, yeast, mold, fungi, and viruses. Essentially, it is a thermodynamic measurement that indicates the availability of water in the product
While water activity measurements help to determine how easily microorganisms can grow in a product, moisture content measurements simply identify the total amount of water in the flower regardless of its availability. This is measured and expressed as a percentage of the total weight of the tested sample and helps to determine a product’s quality and integrity.
Despite the similarities between water activity and moisture content, they are two separate measurements that require different methods of testing.
How water is detected by a cannabis testing laboratory
Water activity is measured through a water activity meter, which determines the amount of available water in a sample. Water activity metering utilizes advanced equipment to detect and quantify pressure. The water activity meter is a closed chamber that measures the ratio of the water pressure of a manufactured cannabis product, against the water vapor pressure of water under the same conditions. This measurement is expressed on a scale of 0.00 to 1.00 aW, where 0.00 is no water and 1.00 is pure water. The abbreviation aW stands for “water activity.”
Water activity is checked in all different types of cannabis products, such as flowers and edibles. Typically, a cannabis flower sample has to clock in at 0.65 aW or under to meet state requirements for sale in a dispensary. Anything higher can cause susceptibility to contamination and degradation of phytocannabinoids, both of which ultimately lower the overall quality of a cannabis product and may jeopardize consumer safety.
This stands in contrast to the process of measuring moisture content, which is performed by weighing the sample before exposing it to high temperatures to evaporate the water contained within the flower. After evaporation, the sample is weighed again and the difference between the two weights is recorded as moisture content. Moisture content is expressed as a percentage, where cannabis products should typically fall between 6% to 15% moisture content, with optimal levels between 6% to 9%.
Is water activity a better measure for cannabis quality and safety?
Water activity is the superior measure of cannabis quality and safety compared to moisture content. It is a more accurate method of predicting a product's susceptibility to microbial contaminants like fungi, mold and yeast.
Moisture content is generally only used to determine how much of a sample is “dry weight,” in order to more easily calculate important information such as the potency of THC as a percentage. Measuring water activity, on the other hand, demonstrates what percentage of that water is considered “free” or “available” for contaminants like microbes. Both moisture content and water activity are important, but it is the availability of the water that really matters for the shelf-life of cannabis flower.
In addition to providing higher-quality, fresh products, an understanding of water activity may also allow manufacturers to predict shelf life and thus establish an ideal water activity specification for products in the future. The importance of water activity testing is proven in and outside of cannabis. In fact, the practice of water activity measuring carries over from the food safety world, where it is essential for the safety of all packaged goods.
Is water activity and moisture content testing required in NJ?
Currently, New Jersey requires water activity level and moisture content testing.
While consistent watering is important to cannabis during the growth cycle, too much moisture is the enemy of harvested cannabis flower. As a result, many states with medical and adult-use cannabis programs require water activity and moisture content testing of cannabis flower and edibles to protect consumers from exposure to harmful contaminants like fungi and mold.
How much available water is in your cannabis flower?
At True Labs for Cannabis, our NJ-based third-party analytical laboratory offers a full suite of objective testing services so you can receive accurate assessments of your products before they head to market. In addition to moisture content and water activity analyses, our laboratory is equipped to test for many other potential contaminants and consumer safety requirements.
By working with True Labs for Cannabis, you can provide your customers with cannabis products that have been evaluated properly, each and every time. For more information on water activity and moisture content testing, check out our full list of services or contact our team.