Moisture content and water activity
Two numbers that decide whether a product moulds: total moisture, and how much of that water is available to microorganisms. They are not the same measurement and a product can pass one while failing the other.
- Pricing
- Quote on request
- Turnaround
- 3–5 business days
- Family
- Analyte panel
Contact us to confirm the sample matrix, analytical scope and price before shipping.
- Calibrated aw meter
- Moisture balance
- Karl Fischer titrator
Purchased new through authorised channels, performance-qualified by certified engineers, and the instrument ID prints on every certificate. View the bench.
What the panel measures
| Test | Method | Instrument | Reports as |
|---|---|---|---|
| Water activity, aw | MethodCapacitance hygrometer at 25 °C | InstrumentCalibrated aw meter | Reports asaw to 0.01, temperature stated |
| Moisture, loss on drying | MethodGravimetric at 105 °C to constant mass | InstrumentMoisture balance | Reports as% w/w |
| Moisture, Karl Fischer | MethodVolumetric titration | InstrumentKarl Fischer titrator | Reports as% w/w, for low-moisture and hygroscopic material |
| Equilibrium check | MethodRepeat aw after equilibration | InstrumentCalibrated aw meter | Reports asDrift reported if unstable |
| Risk interpretation | MethodAgainst microbial growth thresholds | InstrumentDerived from the assay | Reports asMould, yeast and bacterial risk stated |
Sample requirements and shipping
| Item | Requirement |
|---|---|
| Flower or dried botanical | Requirement5 g in a sealed, near-full container |
| Powder or capsule | Requirement10 g or 20 capsules, sealed |
| Edible or baked product | Requirement3 units, unopened |
| Condition | RequirementSeal it immediately after taking the sample. A bag left open for a day reads the room, not the product. |
Confirm the scope and quote before shipping. Shipping instructions follow the agreed testing order. We accept no walk-in drop-off, and we hold no DEA registration, so no Schedule I to V material.
Why the method matters
Water activity, not moisture content, governs microbial growth. A product at 10% moisture can sit at 0.55 aw and be stable, or at 0.68 aw and grow mould, depending on what the water is bound to. Reporting both is the only way to make sense of a borderline lot.
Karl Fischer is the right method below about 2% moisture, where loss on drying cannot separate water from other volatiles. We pick the method by matrix and print which one ran.
What comes back
A public certificate
Every result, the method, the instrument ID, the LOD and LOQ and the signature, verifiable by accession number with no login.
The filmed route
Your package opened on camera, a photograph of each container, and the footage retained for three years. Released to you on request.
A retained sample
Held 90 days, so any result can be rechecked by us or by an accredited laboratory of your choosing.
Questions about moisture content and water activity
Which number does my buyer want?
Cannabis and hemp buyers usually specify water activity, commonly 0.55 to 0.65 aw for flower. Supplement and food buyers more often specify moisture. Ask; we run both on the same sample for less than two separate submissions.
How fast is this?
3–5 business days, faster than most of our panels because there is no chromatography involved.
Does packaging affect the result?
Yes, strongly. Ship in a sealed, near-full container. A half-empty bag equilibrates with its own headspace and the number moves.
Can you run this alongside shelf-life work?
Yes, and it is the usual starting point. Water activity at day zero predicts most of what a stability study will find.
Confirm testing scope
Order in the builder, pay, and a prepaid label is emailed to you. The certificate publishes to the database the moment it is signed.