How Water Activity Prevents Microbial Growth
There
are specific measures for what we call water activity; another way of saying
water activity is internal relative humidity. All those little air pockets
inside of the cannabis flower will have a certain relative humidity, which is
going to be the same as the water activity in the cannabis plant material
itself. There are certain levels of water activity where microbes can grow, for
example, the bacteria that we’re worried about grow above the 0.85 water
activity level. There are yeasts and moulds that grow in the area between 0.65
and 0.85 water activity, where 0.65 is the accepted limit for mould growth in
cannabis.
Most
of your moulds are not going to grow below 0.70 water activity, but some can
grow down to 0.65 and there are a few others that can grow down to 0.60 water
activity, but those are much less common and not really a concern in cannabis. Values
below 0.65 water activity is considered the safe limit for cannabis flower.
There are specific levels for water activity below which microbes cannot grow.
It doesn’t matter how much water is in the cannabis or in any given product,
but it’s a specific level of water activity that determines whether or not
microbes can grow.
Water Activity and Government Compliance
Because
this issue with microbial growth is based on water activity, there are specific
government compliance parameters for a variety of different products that need
to be kept shelf stable. Cannabis is one of those, and there are standards set
up in order to help people maintain compliance. One of the standards for
cannabis is the ASTM D8196 for determining water activity in cannabis flower.
The Water Activity Sweet Spot
for Cannabis
That space
between 0.55 and 0.62 water activity tends to be the sweet spot where those
moisture levels are just right. Anything above 0.65 you’re going to have
potential for microbial growth, so, we really want to be below 0.65. A little
bit lower than 0.65 is always helpful because you want to make sure that you’re
not going to have issues, give yourself a little bit of leeway, but you also
don’t want to be too dry.
If
you get too low in water activity level, it causes oxidation of the trichomes,
and you have a reaction that leads to loss of terpenes and cannabinoids. If
you’re too high in water activity, then the challenge is that you’re going to
have fungus growth, yeast growth, or other microbe growth, so maintaining that
water activity is really important.
Water Activity: Fast and Accurate to ±0.003
Something to look at when you’re looking at water activity is that water activity is temperature dependent; as a general rule, higher temperatures lead to higher water activity. For any given product, the change in water activity based on temperature is going to be consistent for specific products. Also, in cannabis, you’ll see that higher temperatures lead to increased rates of decarboxylation. That means we want to maintain a level of water activity or relative humidity in your cannabis flower, even when it ships for distribution and sale. So, if your product does experience higher temperatures, you may see higher water activities that may put you over the acceptable water activity limit, where you might see some microbial growth.
Being
able to protect that humidity level when product leaves your facility and
before it’s consumed is important, and you’ll want to be aware and give
yourself a little bit of extra leeway. Being closer to the 0.60 or 0.62 water
activity level is probably better than being right at 0.65 water activity in
case there are temperature fluctuations that the product experiences after it’s
packaged.
If
you’re looking at 60% relative humidity, that’s the same as saying 0.60 water
activity. Relative humidity is expressed in a percent. Water activity doesn’t
really have a unit, but we call it water activity or aw. So, it’s
the water activity that determines whether or not mold fungus or microbes can
grow, and its water activity that determines quality, meaning chemical and
physical reaction rates.
At BloomLabs, we can get an accurate measurement to ± 0.003 aw and a precision of 0.002 aw, which is a very, very specific measurement! You can contact us at bloomlabs.ca to receive more information about our cannabis testing!
To sum up, we want to dry the product to the right water activity level to hit the sweet spot so that we’re not over drying, causing quality loss and less sales profit, but also, we don’t want to under dry to enable mould and microbial growth!
Posted
By: Jay Radadiya