Guide 06
Why your jar is drier than its report
A lab report describes a sample on the day it was tested. Two readings on it say something about how dry the flower was, and they don’t measure the same thing. Here’s how to read them, and why the jar in your hand may not match.
In short
- Moisture is how much of the sample’s weight is water. Water activity is how much of that water is free. The two can disagree.
- An industry standard sets 0.55 to 0.65 water activity for dried flower. Above 0.65, mold and other microbes become a risk. Below 0.50, the standard’s publisher says, terpenes dry out and taste and smell weaken.
- Some reports print only Pass, and some put the numbers on a later page.
- A report is a snapshot of test day. In a storage study, terpenes fell under every condition tried.
- NOSE shows water activity against that range, moisture as a plain number, and the harvest or report day with how long ago, when it can read one.
Two numbers for water
Moisture content is the share of the sample’s weight that is water: 11% means 11 grams of water in every 100 grams of flower. Water activity (aw) is a 0-to-1 measure of how much of that water is free, rather than held in the plant itself. ASTM International, which publishes the standard below, calls water activity the better measure for flower because it reads that free water (ASTM, Standardization News).
The two are related, but not by a fixed rule, so two reports can disagree:
| Report | Moisture | Water activity | Against 0.55–0.65 |
|---|---|---|---|
| Report X | 12.8% | 0.53 | Below |
| Report Y | 10.4% | 0.61 | Inside |
Made-up values, to show that one number doesn’t tell you the other.
Report X holds more water by weight, yet its water activity is lower, below the range. Going by moisture you’d call X the moister of the two; going by water activity, it’s the drier one. That’s why NOSE judges water activity and shows moisture without a verdict: we found no published moisture range for flower to judge it against.
The range, and its two edges
ASTM D8197, an industry standard for storing dried flower, sets water activity between 0.55 and 0.65. Its active edition is D8197-22 (ASTM D8197-22). Each edge has a reason:
- Above 0.65, ASTM’s explainer says, flower is at risk of mold and other microbes growing (ASTM, Standardization News).
- Below 0.55, the standard’s own summary says, flower breaks apart more easily in handling and storage (ASTM D8197-22).
On aroma, the explainer says that below 0.50 the terpenes in flower dry out, and its taste and smell weaken. That figure is 0.50, not the range’s 0.55. Neither source says what happens to aroma between the two, so NOSE doesn’t say either. It reports where a number falls against 0.55 to 0.65, with both edges counted as inside.
When there’s no number
Not every report prints one. Some print only Pass for moisture and water activity, which tells you the sample met a limit, not where it sat. Some put the readings on a later page than the terpenes, so read to the end before deciding they aren’t there.
When NOSE finds no number, the card says “no number on this report.” It says the same for a report that prints only Pass as for one that prints nothing, because the two look the same to it.
A report is a snapshot
A report describes the sample on test day, and many print two dates: when the plant was harvested and when the sample was tested. Terpenes keep evaporating and breaking down after that. In a storage study that kept dried flower for up to a year at four temperatures, terpenoid levels fell under every condition tried, on average by more than half within four months (Milay et al., 2020). That’s an average across compounds and conditions, not half lost under each one.
A quieter jar isn’t necessarily a different one. In a study of dried flower irradiated with gamma rays to kill microbes, some terpenes fell while the profile stayed qualitatively the same (Hazekamp, 2016); its author works for the company that supplied the flower. But how much quieter your own jar has become since its test, or whether its balance has moved, no report can say.
What NOSE shows
When NOSE reads a flower report, its card shows:
- Water activity: the number and where it falls, for example “0.53 — below ASTM D8197's 0.55–0.65 range for dried flower.” Those words link back to this page.
- Moisture: the number with a percent sign, and no verdict.
- The harvest day, or else the report’s date, and how many days ago that was, with a note that a report describes the jar on test day. NOSE doesn’t read the test day itself yet, and many reports give neither day in a form it can read, so many cards show no date at all.
None of these changes the match score. The score compares the terpene mix alone (see intensity versus character).
Sources
The standard and studies this guide draws on.
- ASTM International. D8197-22, Standard Specification for Maintaining Acceptable Water Activity (aw) Range (0.55 to 0.65) for Dry Cannabis Flower Intended for Human/Animal Use. store.astm.org/d8197-22.html
- ASTM International, Standardization News. Two Cannabis Standards You Should Know About. sn.astm.org/node/2445/printable/print
- Milay L, Berman P, Shapira A, Guberman O, Meiri D (2020). Metabolic profiling of Cannabis secondary metabolites for evaluation of optimal postharvest storage conditions. Frontiers in Plant Science 11:583605. doi.org/10.3389/fpls.2020.583605
- Hazekamp A (2016). Evaluating the effects of gamma-irradiation for decontamination of medicinal cannabis. Frontiers in Pharmacology 7:108. doi.org/10.3389/fphar.2016.00108