Moisture Content vs Water Activity in Cannabis: Why It Matters for Quality & Shelf Stability
Moisture content and water activity are two of the most important measurements used to evaluate cannabis quality, safety, and long-term preservation. Although these terms are frequently used interchangeably, they each measure a different aspect of how water behaves within cannabis flower—and that difference has major implications for microbial growth, potency retention, and product shelf life.
Understanding the difference between moisture content and water activity enables cultivators, processors, and retailers to produce cannabis that remains safe, stable, and compliant during drying, curing, packaging, and storage.
What Moisture Content Tells You About Cannabis
Moisture content measures the total amount of water held inside cannabis material, expressed as a percentage of the product’s weight. If moisture levels are too high, cannabis becomes vulnerable to mold, yeast, and bacterial growth. Excess moisture also degrades terpenes and cannabinoids, shortening shelf life and reducing product value. Conversely, cannabis that is too dry becomes brittle, harsh to smoke, and more prone to loss of potency through terpene evaporation.
Industry-standard moisture content for cured cannabis typically falls between 10% and 15%. Maintaining this range requires controlled drying rooms, calibrated dehumidifiers, and proper long-term storage conditions to prevent fluctuations that could compromise quality.
What Water Activity Measures in Cannabis
Water activity (aw) measures how much of the water in cannabis is “available” to support microbial growth. Expressed as a value from 0.00 to 1.00, water activity is directly linked to mold risk. Even if moisture content seems acceptable, high water activity can still indicate unsafe conditions if the water is not tightly bound within the plant tissue.
For cannabis flower, the ideal water activity range is 0.55 to 0.65. Within this range, cannabis remains stable—moist enough to preserve terpenes and cannabinoids, yet dry enough to prevent mold. Samples above 0.65 aw have elevated risk of microbial contamination, while samples below 0.55 aw may become overly dry, brittle, and prone to potency degradation.
How Moisture Content and Water Activity Are Measured
Moisture content is typically measured using a moisture analyzer, which determines the total water held within the sample. These instruments may use infrared heating, halogen lamps, or other technologies to accurately quantify moisture loss during controlled drying.
Water activity, in contrast, is measured using a dedicated water activity meter. These instruments assess vapor pressure or relative humidity in a sealed chamber, converting that reading into an aw value. Water activity testing gives processors a direct indication of microbial safety and is essential for ensuring product stability in packaging and distribution.
Why Understanding Both Metrics Improves Product Safety
A cannabis sample can have high moisture content but low water activity—or vice versa—depending on how the water is bound within the plant structure. Because of this, relying on only one measurement can create blind spots in quality control. Using both values together ensures:
- Safer long-term storage
- Reduced risk of mold and bacteria
- Improved terpene and cannabinoid preservation
- More consistent product quality
- Better compliance with state testing regulations
Recommended Tools for Accurate Cannabis Moisture & Water Activity Testing
ARES Scientific supplies high-accuracy instruments and support tools that help cannabis facilities achieve consistent and compliant results, including:
- Ohaus Moisture Analyzers
- Benchtop Lab Instruments
- Metro WavDri Cannabis Drying Trays
- Ohaus Precision Scales
- Glassware & Equipment Washers from Miele
Contact ARES Scientific today for assistance selecting cannabis testing and processing equipment for your facility.
Frequently Asked Questions (FAQ)
What is the difference between moisture content and water activity in cannabis?
Moisture content measures the total amount of water in cannabis, while water activity measures how available that water is for microbial growth. Moisture shows quantity; water activity shows microbial risk.
Why is water activity important for cannabis safety?
Water activity directly determines whether mold, yeast, or bacteria can grow. Keeping cannabis between 0.55–0.65 aw minimizes microbial risk while preserving flavor and potency.
What is the ideal moisture content for cannabis flower?
Most cannabis is best stored between 10% and 15% moisture content to maintain aroma, prevent brittleness, and avoid microbial contamination.
How do I measure water activity in cannabis?
Use a water activity meter, which reads vapor pressure or relative humidity inside a sealed chamber and converts it to a precise aw value.
Can cannabis have low moisture but high water activity?
Yes. If the remaining water is loosely bound and readily available for microbial growth, water activity may still be high even if overall moisture is low.
