Just guessing is totally fine – it's only about a first impression.
Botrytis and mildew do indeed need living tissue. But there is a second group that needs the opposite: decomposers. For them the work only begins once the plant is cut. So the harvest isn't a finish line, it's a change of opponent.
The fungi that turn up after harvest are a different category from everything so far in this course. The textbook puts it so clearly you can hardly improve on it: storage organisms are saprophytes, not pathogens – they can only invade dead plant material after harvest.
Four genera dominate: Aspergillus, Penicillium, Rhizopus and Mucor. They are the same organisms that mould bread and decompose compost. They attack nothing. They tidy up.
Everything else follows from that: whoever tidies up needs no living target – only material and water. So nothing that helped against Botrytis helps here. No site, no airflow, no variety choice. There is only one lever left, and it's called water.
One more honesty: saprophyte is the rule, not a law of nature. Penicillium on living flowers has been described. But the rule holds.
Almost everywhere you read percentages: ten per cent moisture, twelve, thirteen. It sounds precise and it's the wrong variable.
What matters is not how much water is in the material but how much of it is available. Part of the water is bound to sugars and cell structures and is available to no fungus. This available fraction is called water activity, aw for short, running from 0 to 1.
The industry standard for dried flower sets a band of 0.55 to 0.65.
And now the point that surprised us during the check: the same standard expressly rejects moisture content as a control variable. It writes that total water measurements do not necessarily reflect the water available for microbial growth and are therefore an inaccurate means of controlling it.
So there is no fixed conversion from aw into per cent – it depends on variety, sugar content and the structure of the flower. The conversions in circulation appear in no standard. Which is why none appears here.
The target band is 0.55 to 0.65. The upper limit makes sense – above it mould grows. But why is there a lower limit? Drier ought to be safer.
Because the lower limit has nothing to do with hygiene.
The standard states literally what it's for: to prevent physical damage through breakage in routine handling and storage. Over-dry flower crumbles.
So the band isn't a hygiene band at all. It's half microbiology, half product protection – and only one of its two limits protects you from mould. The other protects the goods from you.
That's more than a curiosity. Anyone believing 0.55 to be a microbiological floor might think going below it is risky. It isn't. It just gets crumbly.
And the standard gives no evidence at all for the 0.55 – unlike for the upper limit. It's established practice, not a measured breaking point.
Below about 0.7 most fungi stop growing. The word "most" matters – there are specialists that cope considerably drier, in the lab down below 0.6.
And something else belongs here: Aspergillus and Penicillium survive at water activities between 0.62 and 0.70. They grow poorly there, but they don't die.
The standard says this about itself with refreshing clarity: controlling water activity is not a kill step, it serves to prevent growth and proliferation.
For you that means: properly dried material isn't sterile. It's paused. If it later gets damp again – a poorly sealing jar, a cold cellar with condensation, a container closed too early – then what follows isn't a new infestation but the continuation of a paused one.
The target band isn't a one-off achievement during drying. It's a state that storage has to maintain.
Freshly cut material has a water activity near 1. The target band is at 0.6. In between lies the range where decomposers work best – and the material has to pass through it.
Drying isn't a protective measure with side effects. It is the danger zone itself.
That creates a conflict worth knowing about. Drying slowly and cool is good for aroma and terpenes – the hashish course says so. But it also means staying in the zone longer.
That's no argument against slow drying. It's an argument for doing it in a controlled way: with air movement, without dense packing, and with an eye on the wettest spots – the thick stems and the interior of the largest buds.
A note on honesty: this reasoning is a mechanistic inference, not a measurement. That the zone is crossed is undisputed. How steeply the risk rises with time spent in it, nobody has quantified for cannabis.
Water activity is measured with a lab device, and nobody has one at home. But there's a shortcut based on pure physics.
Seal material in an airtight container and wait, and an equilibrium establishes itself between material and air. The humidity in the jar rises or falls until it matches the material's water activity. After that nothing changes.
And this settled value is the water activity – multiplied by a hundred. An equilibrium humidity of 62 per cent in the jar corresponds to a water activity of 0.62.
A small hygrometer in the storage jar thus makes this lesson's invisible control variable visible – for a few euros and without a lab.
Two things belong with it: the jar has to be genuinely airtight, and you have to wait until the value stops moving. Read it after ten minutes and you're measuring the air from before.
It's the only route to proof in this course that you can simply set up on a shelf.
A fungus that can form a toxin only does so under specific conditions – the moisture and temperature requirements for toxin formation are narrower than those for growth. On top of that, a considerable share of the relevant strains doesn't produce toxin at all, because the responsible gene cluster is defective. Even detecting the gene isn't enough – present doesn't mean active.
And the reverse holds too: no fungus detected doesn't mean toxin-free. Toxins are chemically stable and outlast the fungus that made them.
In some countries material is irradiated to reduce germ counts. What that achieves is well studied – and different from expectations in two directions.
It lowers germ counts by orders of magnitude, but not reliably to zero. Viable fungi were detected in commercially irradiated material; the authors expressly write that complete sterilisation was not achieved. "Irradiated" means reduced, not sterile.
And it destroys no toxins. A poison present before irradiation is still there afterwards. The treatment kills the producer, not the product.
There's also a quirk worth knowing when reading lab reports: after irradiation the DNA of the killed fungi remains detectable. A DNA-based test can therefore come back positive while nothing is alive any more. Literally in the literature: the genetic material of killed organisms remains in the irradiated product.
A positive test doesn't mean alive. A negative test doesn't mean toxin-free. These are different questions asked of the same sample.
Where cannabis is sold under regulation, a mycotoxin test is usually mandatory. That sounds reassuring, and it is – until you look at what gets tested.
For five toxins. Essentially the same five worldwide.
Four aflatoxins and ochratoxin A. That's it. There are over twenty relevant mould toxins, and the panels cover these five.
What happens when someone searches more broadly was shown by a study of seized material: in about 16 per cent of samples toxins were found – overwhelmingly ones no panel checks. Mostly Fusarium toxins, that is, poisons from the same pathogen group that sat on the roots in lesson 2.
The test only looks where the law looks.
That's no scandal and no reason to panic – the five regulated ones are the best studied and most dangerous. But it's the core of this whole course in one sentence: a negative result answers exactly the question that was asked. No more.
And it's a clean example of how "tested" and "safe" can come apart without anyone lying.
On mould toxins two statements circulate that are both almost right. Almost.
"There is no aflatoxin on cannabis." The origin is solid: in the only experiments that produced it, the material had to be autoclaved, watered and inoculated – under normal storage conditions nothing was found. But there have been positive reports since. All come from rapid tests, and where mass spectrometry was used to verify, results stayed negative; in one case the confirmation method's detection limit was even above the reported values.
So the correct phrase is "practically never", not "never".
"Legal material is clean, black-market material is contaminated." Sounds plausible. But the review the figures come from states itself that there are no comparative studies. And in an examination of 118 seized samples, exactly one ochratoxin value and not a single aflatoxin were found.
The seemingly dramatic contrast arises because one number counts detection limits and the other limit exceedances. Those are two different questions, and comparing them yields not a difference but an artefact.
A figure from a large analysis of insurance data is often quoted: cannabis users have a 3.5-fold increased risk of invasive fungal infections.
The figure is correct. And without the following three sentences it is misleading.
First, in absolute terms: it's about five additional cases per 10,000 people per year – 0.08 against 0.03 per cent. A factor of 3.5 on a very small number remains a small number. This absolute figure belongs next to every mention of the factor.
Second, and here we corrected ourselves: it does not affect only the immunocompromised. Among those affected in the analysis, 57 per cent were not immunocompromised. Immune deficiency raises the risk considerably but is not a precondition. We had phrased this differently at first and had to withdraw it.
Third: it's a correlation from billing data of a single year. The authors themselves write that they could not determine the source of infection and infer no causality.
That's the whole truth: a real, small, unevenly distributed risk – and the best lever against it is the drying this lesson is about.
Tap the left side first, then the matching item on the right.
All four pairs share a structure: one figure sounds like an answer but answers a different question from the one you asked. That's not pedantry – it's the difference between a finding and its meaning.
Tap the steps in the correct order.
The fourth step is the one almost everyone skips. A finding is not an answer but an answer to a particular question – whether it was yours is for you to decide. That's exactly what this course was: not knowing more diseases, but knowing better what not-knowing means.
🎯 Hands-on mission
Put a small hygrometer in a sealed storage jar and note the value in your grow diary every day for a week. The first day tells you little – it gets interesting once the value stops moving. Then you've measured the variable this entire lesson was about.
To the grow diary →✓
That's all three rooms. What remains is the question you started with – and three ways to answer it.
Something still unclear?
✓ Thanks – your question reached us. We will reply by email.
