The Importance of Water Activity
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In simplest terms, Water Activity (aw) describes how much moisture is available in a product to support the growth of microbes.
The confusing part is that this is entirely different from the % moisture, which tells you the actual moisture content in the item.
If you're new to this concept, you've no doubt found yourself wondering, "Why not just use the simple term "moisture content" that everybody can understand because it's self explanatory and SIMPLE?"
Water Activity, abbreviated as lower case aw, is NOT a simple concept, but if you intend to sell cannabis, or for that matter ANY food product, you absolutely must understand why it is important.
Ok, so what's the big deal about available moisture?
Here's a simple explanation:
Water Activity and Relative Humidity appear to be pretty much the same thing but they use a slightly different scale of measurement because they actually measure different aspects of the same thing.
RH measures how much moisture the air can HOLD.
Water Activity measures how much moisture a product can RELEASE.
Now let's throw in some specific details about microbes to see how important Water Activity is to your cannabis farm.
In the article: EFFECT OF WATER ACTIVITY ON MOLD GROWTH AND MYCOTOXIN PRODUCTION by: D. Richard-Molard, L. Lesage and B. Cahagnier, we can find some really specific details about how Water Activity affects specific groups and species of microbes.
The following are a few excerpts from the article, re-composed by me for clarity.
Out of about 5000 genera of fungi now recognized, only eleven contain species that can live and reproduce below 0.85 aw. These are called xerophilic or xerotolerant species, meaning they can live in very dry environments. There are a very few extreme xerophile species that are adapted to grow and reproduce to down in the 0,62 - 0,65 aw range.
Xerotolerant molds, which belong mainly to genera Aspergillis, Eurotium and Penicillium, are also characterized by a very high ability to sporulate. Thus they have a great ability to disseminate which probably explains the high frequency of contamination in the agricultural and food industries and more particularly in products with medium or low moisture content, in the range of 0,90 - 0,60 aw.
Long believed to be harmless, molds, or at least some of them, are now known to produce molecules highly toxic for man and other animals. Fortunately, few of the "real" xerophiles are toxigenic and there are few reports of mycotoxin production below 0,85 aw.
Xerotolerant molds occur everywhere. The primary inoculum for most of them is found on decaying plant material and agricultural products of plant origin are always, but generally scantily, contaminated in the field. Due to this constant contamination, food spoilage by molds depends mainly on environmental factors, the water activity being doubtless the most important to be considered.
Foodstuffs with water activities above 0,90 - 0,93 are generally more subject to rapid bacterial spoilage than to fungal spoilage (see below). This is not because fungi cannot grow at so high aw, but because in such conditions bacteria are highly competitive, growing faster than yeasts and molds.
As you can see in this graph, bacterial growth requires a very high moisture content, (27% or more) so bacterial infection is not going to be a common problem in cannabis drying rooms, barring accidental or negligent circumstances.
However, yeast are still able to grow or to slowly develop fermentative activities below 0.8aw in products with high sugar or salt contents such as jams, dried fruits, honey, dry sausages and hams. As a general rule, yeasts prefer liquid or semi-liquid media probably due to their relative "immobility" and tolerance to anaerobic conditions. Cannabis is neither high in sugar or salt, nor liquid, so yeast is highly unlikely to cause any issues in the average cannabis drying and curing process.
With Molds, the attitude of consumers depends to a large extent on the visual aspect and obvious mold development is the main factor in refusing finished products even if they do not contain toxic metabolites. To prevent the visual appearance of molds, the understanding of mechanisms governing the growth and sporulation of molds is of the utmost importance in the food industry.
In addition, it must be emphasized that the available detoxification methods are still unsatisfactory for technical or economical reasons which most often leads to disposal of infected crops, so prevention becomes the primary focus.
While some Fungi may be able to live at 0.62 and higher, aw levels above 0.7 are required for molds to reproduce, so for practical purposes, maintaining aw above 0.7 will limit sporulation which severely diminishes the ability of fungus species to complete their life cycle.
Some of these toxic fungal metabolites, such as aflatoxin BI, are carcinogenic, the others producing various disease syndromes, so that every effort mus-t be made to prevent food contamination by mycotoxins. Mycotoxigenic fungi are principally found in three genera : Fusarium, Aspergillus and Penicillium.
Some of the limiting aw values for mycotoxin production are listed here.
The lowest aw levels permitting aflatoxin BI biosynthesis are near to 0,80 but limiting values of 0,83 - 0,85 were frequently reported.
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Penicillic acid is also only produced at 0,80 aw and above.
As a general rule, it is considered that the limits of toxin production are higher than those for growth.
It seems that for processed foods and cannabis, mycotoxin poisoning presents a limited risk for several reasons:
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Can smoking cannabis lead to fungal growth infections in your body?
(Note: this is different from the potential of poisoning from fungal toxins. This is talking about infection where a fungus is actually growing in or on your body.)
According to this survey by the CDC, the difference between fungal infections found in cannabis smokers -vs- non cannabis smokers was 0.03 vs 0.01. Of course the big header right below the title was... "A new study suggests that cannabis use could lead to potentially life-threatening fungal and mold infections, especially for people who are immunocompromised." (In this case, immunocompromised meant AIDS)
Despite the statistical insignificance of the difference between .03 and .01, they went on to say this...
"...persons who used cannabis appeared to be sicker than persons who did not use cannabis and were therefore presumably at higher risk for fungal infections in general."
Just a second... let me get out my meter... yep, just what I thought.
What does all this mean for Cannabis Farmers??
In general, you DO absolutely need to monitor Water Activity as you dry and cure your crop.
However according to these sources, the risks from mold toxins are extremely low (like off the chart) once you get below 0.8 aw.
The risk from an actual bodily infection of any mold due to smoking cannabis, is astronomically low.
Aside from the health benefits, why should you monitor Water Activity?
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Solid!
Head grower
2 年This is a big concern, good read.Thanks for sharing this article