Education Guides

Water Activity Cannabis Testing Guide

Cannabis water activity processors have a tight moisture target to hit when drying. Too dry, and you destroy trichomes and profits. Too wet, and you get mold, sick customers, and a damaged reputation.

How do you get the precision you need to hit the sweet spot? And how do you package to make sure you stay there?

Water activity/RH works in tandem with moisture content to transform the way you monitor and control moisture during drying, packaging and storage. Result: a level of control over your process that allows you to consistently hit the sweet spot that maximizes profit and guarantees safety and quality. In short, in this water activity content cannabis testing guide . . .

You’ll learn:

  • what water activity is and why it’s an essential measurement for cannabis processors
  • what you need to know about how water activity predicts microbial growth
  • how to use specific water activity limits to maximize quality and minimize destruction of terpenes
  • why you should control water activity in the drying process to maximize profitability, control potency, and guarantee safety
  • how to prevent over-drying and excessive weight loss in the drying, curing, packaging, and storage phases

Brian Rice, Director of R&D at Boveda, and John Russell, METER Food Application Support Specialist, will co-present. The webinar will be followed by a 10 minute live Q&A with the presenters.


John Russell is an Application Support Specialist with 25 years of food safety experience, 13 of those spent helping food and pharmaceutical manufacturers use water activity to improve safety and quality in their products. In the past 5 years, he has worked extensively with cannabis processors to use both water activity and moisture content measurements to optimize moisture control in their drying and curing processes.

Full transcript

Brad Newbold, Moderator: Hello everyone, and welcome to water activity and cannabis webinar. Today’s presentation will be 30 minutes followed by 10 minutes of QA.

If you have a question during the webinar, type it into the questions pane, and you can submit a question anytime. And we’ll keep track of these to answer during the Q&A. To answer our most commonly asked question in advance, yes, we will be sending out links to the on demand webinar and the slides to everyone who attended today’s webinar. Those will be available a day or two following the webinar.

Today’s webinar will be co-presented by Brian Rice and John Russell. Brian is joining us from Boveda, global leader in two-way in package humidity control for cannabis products, musical instruments, and cigars. Brian is the head of R&D at Boveda with more than 20 years of experience in packaging and new product innovation and is also a leading expert in water activity. He and his team have extensively studied the changes that occur in cannabinoids when stored at various levels of humidity and moisture. And he’s going to share some of that expertise with us today.

John is a longtime Application Support Specialist here at METER group in the AQUALAB division with 13 years of experience helping food and pharmaceutical manufacturers measure water activity to improve safety and quality in their products. In the past five years, he’s worked extensively with cannabis processors to use both water activity and moisture content measurements to optimize moisture control in their drying and curing processes. We appreciate both of them joining us here today to share their expertise. And now I’m going to hand the microphone to Brian Rice who will start today’s presentation.

Relative humidity and Boveda packs for cannabis

Brian Rice: All right. Again, my name is Brian Rice, Director of R&D, Boveda, and we’ll talk to you later about maximizing cultivation profits post-harvest using humidity control.

Four points I’m going to try to drive home today:

First we’re going to understand how evaporation post-harvest affects cannabis.

Second, gain a little understanding of water activity as the recognized ASTM measurement for determining cannabis safety.

Third, learn what is the target moisture level for cannabis flower and understand how it directly impacts cannabinoids.

And then fourth, let’s try to understand how those water activity levels relate to the sweet spot which ultimately drives quality and economic gains.

So who is Boveda? We are a privately held company founded in 1997, headquarters in Minneapolis, Minnesota, and we manufacture and produce two-way humidity control pouches that primarily serve the markets for premium cigars, music, and cannabis.

Let’s dive a little further down into Boveda’s technology. Essentially, it’s a very simplistic pouch. We use biodegradable craft paper. We take that paper and extrude a vapor phase osmosis membrane that’s bonded to the paper. We then take that film and form it into a pouch and fill it with food-grade salts mixed with water and a little bit of gum to thicken it up. All three of those come together to combine and make our patented formula and pouch.

Two-way humidity control

So let’s talk about what is a two-way humidity controller. Essentially what a two-way humidity control will do is add in or remove water vapor as needed to maintain a product at an ideal RH. The water vapor can pass very quickly through the Boveda film to respond to the outside environment; essentially it can bring the contents and internal environment of that container to equilibrium, to whatever RH is printed on our packs. It’s kind of like dialing in the thermostat. It’s a predetermined RH. It gives off water and takes water vapor in as needed to bring it to equilibrium.

What Boveda is not is a one-way humidity controller. Essentially, it’s not a desiccant that is constantly pulling in water to create that dry environment. And it’s not a humidifier (just the opposite) which pushes that water vapor into the environment to create a wet space. So as you combine those two together you’ve got the Boveda.

Alright, so now we know a little bit about what Bovida is and what a two-way control is.

How can you prevent evaporation of terpenes?

The three things I want to touch on next is how can you prevent evaporation of terpenes?

One is that the terpenes maintain the trichome health, and then also a monolayer water that is produced to help preserve and maintain all your terpenes.

A second is how do we control the moisture weight and why it’s critical to maintain its moisture and its economic impact.

And then third, overarching cannabis quality and making sure that your brand reputation is held by preventing mold and potential over dry buds and maintaining fresh and safe cannabis.

So in order to understand how to prevent terpenes from evaporation, we need to understand where terpenes actually reside, and the majority of the terpenes reside in the trichomes. And not only within the trichomes, they reside in the trichome heads. So in the upper left hand corner, you’ll see that the terpenes actually reside in glands that are in the trichome heads along within that trichome head is also some cannabinoids, as well as the outside layer—on this trichome head is a slightly waxy surface layer. So now that we understand where terpenes reside within a trichome, let’s look at what happens to trichomes without humidity control. So this is a snapshot or picture of a zoomed up version of some trichomes on a specific strain. You can see on this picture that the trichome stock is actually thinned out a little bit which isn’t bad and also that the trichome head itself is actually intact. You can see it has maintained its shape, and some are translucent and some are getting cloudy. This looks like a pretty ripe and good trichome in bud.

Now this is a snapshot of that same strain. We’re now looking at one month without humidity control. The heads of the trichome, that bulb shape, is now starting to shrink, similar to what a grape does transitioning into a raisin. And now the stocks have started to dry up even further and started to twist and get a little mangled. This is leading down towards a very dry cannabis sample that probably will not be perceived as visually appealing to any of your customers.

And this is two months, the same buds, same trichome on the same buds. Now the trichome head is not very appealing. And essentially, this is something that could happen within your buds as humidity control is not put in place and allow these trichomes to fall off into the container, therefore creating the kief that’s going to be sitting on the bottom. And I would assume at this point after two months and without humidity control, your bud is starting to turn into dust.

So what’s happening at this stage? We know that water evaporates out of the trichome heads and along with that water, you’re going to get to the flavonoids and possibly some other cannabinoids are going to be exhausted out of the trichome head. It’s very similar to if you have an open container or you have a bud and you open it up that smell that you’re going to get initially of a high terpene smell. That is terpenes that have been evaporated out of that trichome head, never to return back in.

So, overarching how do we prevent evaporation of the terpenes? We do know that dry trichomes are brittle, fragile, and potentially have lost a lot of their potency. ASTM standards are saying that we need to keep this cannabis between 55 and 62 to maintain not only good healthy and hardy hydrated trichomes, but they’ll remain flexible and preserve the cannabinoids all the way through from packing all the way to your consumers. So yep, bad. That’s a bad trichome.

How can you protect cannabis terpenes in storage?

Alright, so now that we understand evaporation and how terpenes can evaporate through that trichome head, how do we protect this a little further? And what happens when your bud is being stored with a humidity control and as your buds start to come into equilibrium with its outside environment, what’s starting to happen is a monolayer of thin water is being formed around the trichome head. Essentially what it’s doing is trapping and making sure that those terpenes and cannabinoids and the water within a trichome still stays within that trichome head. And they’re only to be released once the consumer gets them and grinds it up and then releases that wonderful bouquet.

What I like to tell people is essentially that monolayer is a shield or a helmet that you’re placing over that trichome head until it’s actually consumed by the consumers.

What’s the most interesting is once this monolayer is formed, that smell that you’re most accustomed to getting when you open up a container won’t be there. I can tell you the absence of that terpene smell is good. That means that humidity control has been put in place, that monolayer of water has stopped any evaporation and it is preserved and ready for consumers to open and grind your bud. And we’ve done some significant studies that show there is zero terpene loss when this monolayer is formed and you’re also, by the way, going to keep these trichomes hydrated, healthy, and prevent oxidation moving forward.

Insufficient cannabis packaging means lost revenue

However, evaporation is still a problem. This is a study we did back in 2018. We measured multiple different cannabis dispensaries across five different states and in all different types of styles of packaging, ranging from glass to paper to film. And reality is almost 90% of these fall below that 55%. So 90% of the samples that we tested in 2018, fell below that 0.55. This is dry. We’ve actually even seen some down there at 0.44. Those are the ones that you’re probably going to see a lot of keeping your containers and things are starting to turn into dust.

So let’s look at how evaporation can happen. Things that get out of control and it gets to consumers. You know, you spend all this energy in a production and the harvest. But what about post-harvest? Humidity control can help in every one of these points. In this simple example, you’ve got about eight different touchpoints post-harvest once it’s in a package that evaporation can happen.

So what evaporates between when a bud is harvested on the farm to when it reaches a local dispensary? When water weight is lost, there’s a loss of revenue to you. Dehydrating bud equals loss of terpenes and cannabinoids. And overdry buds, you’re going to compromise your trichome health and probably the overall quality. So let’s look at several examples.

Here we’ve got 1000 pounds of cannabis at standing price in this example of about $5 price per gram. And it starts at 50% humidity. Now let’s look at what happens without any humidity control in a package at a 5% drop in RH is roughly around $15,000 loss just to water evaporation. Think of that—just a little bit of water, 5% of that water leaving is roughly about $15,000. And your trichome has been compromised. All the terpenes have been evaporated. The appearance is horrible. It’s just some really horrible weed coming out of this without humidity control. And by the way, you’re going to get slammed on social media.

This is just a couple of snippets that we’ve pulled—people who are going back to the black market. It’s a hit and miss on quality, the weight is not exactly what’s printed on the package. And by the way, it’s not a US problem. It’s a problem that our neighbors to the north of us, Canada, has this humidity problem, evaporation is the problem.

So as a cultivator you’re not down $15,000 just for that 5% loss. Dispensaries are unhappy because they’ve got really crappy weed. And by the way, the consumers aren’t going to buy it. It’s a lose, lose, lose without humidity control.

Controlling RH maximizes profits

So let’s look at it. You can be saved. Now let’s look at that same example. Your weed starts at 50%, same thing thousand pounds in about $5 per gram. And now let’s just look at if we increase this to 62% using humidity control, just that 12% increase in RH is about $48,000 gain in revenue. And by the way, you’re still keeping your cannabis safe. It’s below a threshold where mold won’t grow. Your trichomes have now formed a monolayer to prevent any terpenes from evaporating and any cannabinoids from being lost. So as a cultivator you’ve increased your ROI just by using humidity control. Your dispensaries are happy. They’re stocking and storing high-quality bud. And your consumers are happy—they’re going to keep going back to the dispensaries and buying. It’s a win, win, win situation.

So overarching, controlling RH maximizes your profits by

  1. you’re going to maintain healthy and hardy, hydrated trichomes.
  2. That monolayer is going to be formed keeping cannabis safe and hydrated between the 55 and 62.
  3. That monolayer of water on the trichomes locks in those terpenes and cannabinoids until the time those consumers purchase it and grind it up.
  4. You’re going to preserve the package weight, prevent mold, and avoid any costly recalls that could happen when it gets into that supply chain that you cannot control.

That’s it. Thank you. And I’m going to turn it back over to John.

Measuring water activity increases cannabis quality and profit

John Russell: Thanks, Brian. You did a really good job of highlighting why it’s so important to maintain the relative humidity in your cannabis and not over dry during drying and at post harvest in all the stages of post harvest.

So I’m going to go a little bit more deeply into what it is that we’re doing when we’re maintaining the relative humidity in the cannabis and drying using water activity as a measurement. So the things that we’re going to cover are microbial growth in cannabis and common molds that you see in cannabis. Also, we’ll talk about how water moves, water activity as a mode of action, water activity standard methods, and also moisture content challenges—why it’s difficult to measure moisture content in cannabis. We’re also going to learn about cannabis isotherms which show us the relationship between water activity (or RH) and moisture content and also how temperature is a factor in that. And then controlling relative humidity in the drying process.

Water activity prevents over dry cannabis and microbial growth

So why do processors over dry? I think that it’s pretty common that people know that you don’t want to have bud that is too wet. So if you dry enough you can avoid the microbial and the mold issues that can pop up. However, if you don’t understand what relative humidity is in cannabis, then it’s difficult to know how dry you need to have the cannabis.

So let’s talk a little bit about microbial growth.

There are specific measures for what we call water activity. Another way of saying water activity is internal relative humidity. So inside the cannabis flower, all those little air pockets inside of the cannabis flower will have a certain relative humidity. That’s going to be the same as the water activity in the cannabis plant material itself. There are certain levels of water activity where given microbes can grow. Now notice on this chart that the bacteria that we’re worried about are above the 0.85 water activity level. Again, that’s the same as saying 85% relative humidity. There are molds and yeasts that are going to grow in that area between 0.65 and 0.85 water activity. And 0.65 is the accepted limit for mold growth in cannabis.

Most of your molds are not going to grow below 0.70 water activity, some can grow down 0.65, and there are a few others that can grow down 0.60 water activity, and those are much less common and not really a concern in cannabis. So below 0.65 water activity is considered the safe limit for cannabis flower. Dr. William Scott in the 1950s did some studies and showed us that there are specific levels for water activity below which microbes cannot grow. So the science has been done, and we know those specific levels like I showed on the chart previously, but it’s water activity and not water content. 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.

So what are some common molds in cannabis? Aspergillus, Botrytis, Penicillium, Cladosporium, Mucor, and Rhizopus. Now Rhizopus especially concerns me because I have a Rhizopus allergy. And I do get weekly shots in order to prevent reactions to Rhizopus. So that’s one that’s really important to me. And why do we want to avoid mold on cannabis? Well, it’s true that when molds grow on your food, if you eat them, there are some mycotoxins that might affect you healthwise, but overall molds aren’t going to get you sick when you ingest them.

However, it’s a little different when you inhale mold spores. So for healthy individuals, if you inhale mold spores and you get a fungal infection in your lungs, it could be much like a chest cold. It’s not a big deal. But what if you’re immunocompromised? Actually a fungal infection to cancer patients, HIV patients, or the elderly can be life threatening, it can be very, very serious. So it’s really important, especially since some of these patients are using cannabis for treatment.

How does water activity prevent molds and microbial growth?

So why is it that low water activity prevents microbial growth? So it has to do with how water moves. So water moves from high pressure to low pressure. Relative humidity and water activity are another way of saying vapor pressure. So inside any given microbe cell, there’s a certain amount of water activity and then there is the cell membrane and the cell membrane maintains a certain turgor pressure.

Now, water moves from high pressure to low pressure. In this slide here you’ll see that in the top left, the microbe cell inside has a water activity of 0.95. That’s another way of saying 95% equilibrium relative humidity. So inside that microbe cell is 0.95. If the environment where that cell is existing has a water activity of say 0.98, then water will move from high water activity to low water activity until it comes to equilibrium.

So water will actually move through the cell membrane as it tries to reach equilibrium. And that cell will then have what it needs so that it can split and create two cells and then you have microbial proliferation. However, if the environment outside of that microbe cell is lower than 0.95, like in this example is 0.90, then water will move out of the cell and it causes turgor pressure loss.

So what does the cell do? The cell wants to maintain that turgor pressure, and so it tries to adapt. So the microbe tries to adapt by altering its membrane makeup, or by reducing its water activity to maintain turgor pressure. It will transport in small solutes to reduce its water activity. And what happens when it does that? If it’s unable to reach that equilibrium with its surroundings, then that cell goes dormant.

Now it’s important to realize that when a microbe cell goes dormant, it doesn’t mean that it dies. So if you are in your grow rooms or growing cannabis and bacteria or mold growth occurs, and the mold growth and microbe count in general is too high, lowering the water activity isn’t going to fix that. It’s not going to kill those bacteria. What it’s going to do is keep them from proliferating. It’s going to keep them from growing. So you do want to be concerned with the potential for introducing microbes into the grow rooms. But if the microbe count is at relatively low levels and passing levels, then you lower the water activity in the dry room to where they can’t grow, and you’ll be able to maintain those levels.

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 with compliance. So one of the standards is for cannabis. And that is the ASTM D8196 for determining water activity in cannabis flower. Now notice that there are also methods for pharmaceuticals, foods, and cosmetics too, and this is a list of some of those methods.

The water activity sweet spot for cannabis

So there is a water activity sweet spot and Brian talked about this. That space between 0.55 and 0.62 water activity tends to be the sweet spot where those moisture levels are just right. This graph here shows you water activity compared to moisture content. This is something we call a moisture sorption isotherm. In this moisture sorption isotherm we can compare the moisture content to the water activity, and in that spot above 0.65 you’re going to have potential for microbial growth. So we really want to be below 0.65. And a little bit lower is always helpful because you want to make sure that you’re not going to have issues, you give yourself a little bit of leeway. But you also don’t want to be too dry. Brian mentioned how you can affect the quality of your cannabis if you go too dry and also the profitability and that’s pretty important.

So you notice that we were showing on that slide on that moisture sorption isotherm that there are specific levels for moisture content you can look at as well. And you can see the relationship between moisture content and water activity. So why not just test moisture content? Well, there are specific challenges associated with moisture content testing. And in cannabis, it’s especially difficult to test moisture content accurately and precisely.

Measuring moisture content is not accurate

For one thing, there’s no standard to test against. Most of the moisture content testing for cannabis is done via a loss-on dry method. In that method, you weigh a sample before drying and then you add heat to dry a sample until it’s totally dry. And then you weigh it again. One problem is that you make the assumption in the loss-on drying method that all of the weight that is lost is due to evaporation of water. And because we know how much water weighs, we can then determine how much of that sample was water.

However, how do you really know that something is completely dry? And the answer is you don’t. And there’s no standard to test against to show that the measurements that you’re getting are true measurements, so there’s no way of knowing that your measurements are accurate. And so because of this, there are many different methods that you’ll see for loss-on drying. And also other methods for testing moisture content, like you may have heard of Karl Fischer. But each of these methods gives you different answers. You might see an oven dry method at 105 degrees for two hours, for example, well, that’s going to give you a different results than if you’re doing a loss-on drying in an oven at 75 degrees for a longer period of time.

So really, it’s difficult to know what the true answer is for moisture content. Also, you don’t know if water is the only thing that volatilizes. This is especially important in cannabis because when you add heat to cannabis, you do cause loss of terpenes and flavonoids and volatiles. The weight that is lost is not just water. So using that loss-on dry method, especially if you are using a moisture balance, adding high heat for a quick measurement (meaning five or ten minutes), a lot of the weight that will be lost is actually due to volatiles in addition to water.

You also see a lack of precision with moisture content measurements. So even with good calibration on a moisture balance, the best you can get with most any product is plus or minus half a percent moisture content. And in cannabis you’ll often see plus or minus 1% moisture content. So there’s a lot of trouble getting a precise measurement as well. So when we look at this cannabis isotherm again, and this time we’re looking at water activity versus moisture content, you can see that that slope is relatively shallow, meaning small changes in moisture content show us large changes in water activity.

Water activity: fast and accurate to +/-0.003

Now with a water activity meter, we can get an accuracy of +/-0.003 aw and you can get a precision of 0.002 aw. So you have a very, very specific measurement. Now with moisture content, if you’re getting +/- half a percent or +/- 1%, then you are not getting a very good idea of what’s happening with the moisture in your product.

Another thing 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. Now for any given product, the change in water activity based on temperature is going to be consistent for specific products. And also in cannabis, you’ll see that higher temperatures lead to increased rates of decarboxylation. So what does this mean? This means we want to maintain a level of water activity or relative humidity in your cannabis flower, even when it ships. So if it does experience higher temperatures, you may see higher water activities that may put you over the limit where you might have more microbial growth.

So being able to protect that humidity level when it leaves your facility and before it’s consumed is important, and also you’ll want to be aware and give yourself a little bit of extra leeway. So being closer to the 0.60 or 0.62 is probably better than being right at 0.65 water activity in case there is temperature abuse that the product experiences after it’s packaged.

Controlling water activity in the cannabis drying process

Okay, so why do we want to control relative humidity in the drying process? A lot of this has to do with what water activity is and what relative humidity is. We’re going back to how water moves (the mode of action for water). Water moves from high relative humidity to low relative humidity until it comes to equilibrium. Another way of saying high water activity to low water activity. So remember, 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.

So this is important and we can go back to what’s happening on the trichome at specific water activity levels. If you get too low in that 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 like bacterial growth if you’re high enough, so maintaining that water activity is really important.

In the dry room, it’s important to maintain that humidity at a level where you don’t over dry because water will move until it comes to equilibrium. If you have the humidity in your room at 40% or 30% you have the potential of drying your cannabis down to 0.40 water activity or 0.30 water activity. The other issue with having over-dry environmental conditions in your dry rooms is that if you dry too quickly, the exterior of the bud can form a crust. We call it case hardening, in which case that can become a moisture barrier. If that happens, the internal moisture is inhibited from moving through the bud and out into the environment. So you might have hotspots of high water activity in the bud. You’re going to have much less conformity in your room in the drying process. And you’re going to see a lot more variation in the buds in the drying process if you’re drying in too low humidity.

So being able to dry down to the right water activity levels and in conditions that bring it to the right water activity levels without over drying is really important. So how do you know when the moisture is right? Unfortunately, moisture content is not adequate. Why? Because it just doesn’t have the precision or accuracy. Water activity is a much more specific measurement. So it’s like measuring to the nearest millimeter rather than measuring to the nearest inch. You know that you’re right on target. If you measure to the nearest inch you might be a little high, you might be a little low, and you wouldn’t know. So that lack of precision becomes a problem for moisture content. And each moisture content method gives you different answers. You don’t know if your measurement is really at the place where it’s going to have the right water activity. So if you measure water activity, to determine that your product is dry enough without being over dry, you can hit the sweet spot every time. Okay, so just to sum up, we want to dry to the right water activity level to hit the sweet spot so that we’re not over drying, causing quality loss and also less profit, but also we don’t want to under dry to enable mold and microbial growth.

Cannabis Q & A

Brad Newbold, moderator: Thanks very much. Okay. Thank you, Brian, and John. And let’s take a few listener questions here. Now, again, there’s still time to ask questions by typing into the questions pane. And we’ll try to get to as many as we can before we finish. So, John, first question for you here. They’re asking what’s the best tool to measure relative humidity?

John Russell: Okay, so if you’re looking at measuring relative humidity in a dry room, then there’s a variety of options available to measure relative humidity. If you’re looking at measuring what is the relative humidity inside the cannabis bud then we call that water activity. One of the best ways to measure water activity in the cannabis flower is a chilled mirror dew point sensor. The chilled mirror dew point sensor is a direct measurement of water activity or internal relative humidity and it gives you very high accuracy. It’s accurate to depending on the meter you have to 0.005 or 0.003. And really good precision. It works very well for cannabis flowers. That’s what I tend to recommend. And there are a few different options for chilled mirror dewpoint sensors in the METER AQUALAB line.

Brad: Awesome. So yeah, if you want to know more information, we’ll give you some links at the end here. Brian, here’s another one. If I under dry my bud will a Boveda pack increase the weight?

Brian Rice: Yes, absolutely. And that’s where that water activity measurement is so critical. If you under dry and you know where your start point would be either adding a Boveda pack for specifically the cannabis ones at 58% or the 62%. It will effectively bring up your Cannabis to that equilibrium to hit that 62 or 58% mark. So whatever that difference is, you will definitely gain that weight back. If it’s over dry, it may take a little bit of time depending upon, obviously how much the volume and the weight of the cannabis that’s stored and how dry it is. But it will work and bring it back up. Absolutely.

Brad: Awesome. Okay, let’s see. John, let’s go back to you. How would you measure water activity in a cannabis product that is in the finished product packaging?

John: Okay, so, generally what we would do is remove a piece out of the finished product packaging. So water activity we do need to take out of the package in order to measure it. So very easy measurements to take. You just put a small sample into a sample cup and set it into a water activity meter and start reading and for most products, you have a read in less than five minutes. So that’s, that’s what you do is you would take random selections of your products and then measure them for water activity.

Brad: Okay, and about what size of a sample would be required for that then

John: About seven and a half milliliters for for most products, so not too big of a sample.

Brad: Okay. All right. We’ve got a couple of questions. John. They wanted some clarification on what you mentioned with the water activity instruments. You mentioned a chilled mirror dew point sensor. Can you go into a little bit more detail about those types of instruments?

John: Yes, absolutely. And if anybody would like specific details, feel free to send contact information to me and I can give much more detailed information. But just to sum it up, what we’re doing when we’re testing water activity is we’re taking samples and setting them into a sample cup and placing it into a small chamber. That small chamber has a sensor in it. And there are a few different kinds of sensors that you can get that will measure the relative humidity inside that chamber after it comes to equilibrium.

In that small chamber, the humidity in the air above a sample is going to come to equilibrium with the sample itself. And so then if we can measure the relative humidity, then we know what the water activity inside the sample is. So a chilled mirror two point sensor. You chill it inside that small chamber where the sample sits. You chill a mirror and until dew forms on the mirror, and at the moment the dew forms on the mirror, take a temperature reading of the mirror and the sample and you can calculate the water activity in that sample.

METER has a chilled mirror dew point sensor called the AQUALAB 4TE. It’s the fastest method available for testing water activity. It’s also the most accurate method that we have available. And has a very consistent calibration, so you get a lot more consistency using a chilled mirror method than you do other methods. Other methods might include capacitance sensor or a tunable diode laser sensor, you see a lot more variety you also see changes in calibration over time with changes in humidity and you need to do more to ensure that you’re going to maintain that calibration. And also, capacitance sensors take much longer to come to equilibrium because it’s not a direct measurement of the air where a chilled mirror dewpoint sensor is a direct measurement of the air.

Brad: Okay, and where can they find those kinds of instruments for purchase?

John: Well, at METER group, we have a variety of options for water activity meters, and so I would recommend that you visit Aqualab instrumentation at the METER group website. And I’d be happy to help direct anyone to that location if it’s helpful.

Brad: A follow up for Brian on the increasing weight question, Brian. If you used a Boveda pack to increase the weight, then would this help increase the quality loss that occurred with over drying or increased potency?

Brian: Yes, that’s a very good question. You know, I think if it is over dry, obviously those terpenes that were there when it is cured properly have been lost. So, I think, unfortunately, a lot of the terpenes will be lost. So if you can prevent and stop them from evaporating even further and and getting to that monolayer is ideal. You know, if we think about you were mentioned the THC, probably the potency, bringing that back, it all depends upon the strain. We haven’t done any significant studies to show whether or not we can revive and bring those back. But, you know, it is something that needs to be explored. You know, it’s all dependent upon the plant and how well it’s growing and the genetics, so. So unfortunately, we can bring back the weight, but the potency of it may have already been lost.

Brad: Okay, let’s see, we’re running a little bit short. And we’ll take one more question. And again, if we didn’t get to your questions, and there’s a bunch that came in, and we appreciate that, we do have them recorded, and we will be able to answer them, either John or Brian or one of our team will be able to get back to you via the email that you registered with. So one last Question, John. And then Brian, if you have any extra thoughts as well, John, measuring water activity, is there a difference between measuring the whole bud versus ground material? And then what about the situation you described with the case hardened bud?

John: sure, that is a really, really good question. So, a lot of times it’s appealing to measure whole bud because water activity is a non destructive test, and so if you can measure the whole bud, you can keep it intact. There are challenges when measuring whole bud especially in the dry room where the interior of the bud is going to be. It’s going to dry at a slower rate than the exterior. And so especially if you’ve dried too quickly and you have case hardening, then when you’re testing water activity, you may not realize that you are not in equilibrium in the chamber. So that can be a challenge, I do recommend breaking up the bud.

And you can break it up either with a little hand grinder or breaking it up even with gloved fingers or a scissors to expose the interior, then you know that you’re coming to equilibrium in a water activity meter, and we’re going to get the correct result. Now, when you go from the dry room into a curing process, if you’re doing burping or you’re doing curing in a bucket or a bag that sealed, those buds are going to come to more equilibrium in the interior and the exterior during that time period of curing, are going to become more uniform. And so then you’re going to have an easier time testing whole bud at that step. Still, it’s recommended that you would break open the bud and expose the interior so that you know you’re getting the true water activity and not just the water activity of the exterior.

Brian: Yeah, I’d have to agree with you too John and a lot of the the testing that we’ve performed not only just with cannabis, but with hemp, you’re going to get the true water activity meter reading in your meter when it’s ground up, and that is typically how, you know the labs test for the COA, they’ll take those buds and you know, and this is a term that they’ll use is homogenize a sample and whether homogenizing it, you’re grinding it up to expose all that the water has been that has become into equilibrium. So I agree with you a hundred percent.

Brad: Okay. Thank you, Brian. Thank you, John, again, and thanks to all of you who’ve attended, we’ve had a great attendance rates. We hope you enjoyed this discussion. And we hope to have more in the future as well. So please visit and for more information on METER Group water activity instruments and Boveda packs and come find us at MJ Biz Con. And within the next couple days, we’ll be sending you an email with links to this recording as well as to the slides. And if you’re interested in webinars on shelf life or other things of that sort, please be sure to let us know in the post webinar poll that will pop up after you close out. And again, thank you, and stay tuned for future METER food webinars. Thanks and have a great day.

If you over dry cannabis and CBN is created, when you rehydrate is the CBN still present?

When moisture levels are in the sweet spot (0.55 aw to 0.62 aw) the protective monolayer of water is intact. When over drying, enough water has evaporated so the monolayer is disturbed, leaving the cannabis flower and trichomes susceptible to reactions with the air. Decarboxylation occurs with added energy from heat or light, or with added time. Without an intact water monolayer, reaction rates with the air increase – even at ambient temperatures albeit much slower than at elevated temperatures. If CBD or THC are created during decarboxylation, they will over time release into the surrounding environment. Adding moisture after the fact, won’t recover what has been lost, and it won’t completely restore trichome health, but if the monolayer of water is reintroduced it can help prevent or slow the rate of reactions with oxygen in the air. Ideally, cannabis or hemp flower is dried to the sweet spot for moisture – between 0.55 aw and 0.62 aw – then stored in humidity conditions that keep it at that sweet spot, or packaged well enough to prevent moisture exchange with the surrounding environment.

Measuring water activity – is there a difference between measuring a whole bud versus ground material? What about a situation as described with a case-hardened bud?

It’s advisable to measure bud which has been hand ground, broken up, or cut to expose the interior. When testing the whole bud, especially when case hardening occurs, you are likely to have inaccurate results because the sample won’t come to full equilibrium in the chamber. After being stored in a closed container for a period of time, you will see more uniformity between the interior and exterior of the bud, but to be safe, exposing the interior during testing is best. Electric grinders can add heat from friction, causing moisture loss, and isn’t recommended.

What is best equipment for measuring water activity in finished products such as baked goods, bar soap, or deodorant sticks?

If your products contain alcohol, propylene glycol, essential oils, or other aromatic volatile ingredients, the AQUALAB TDL will be able to test all of your products with high accuracy. The TDL uses a laser to which has been fine tuned so that it only detects water vapor and no volatiles will interfere.

If your products don’t contain the aforementioned volatiles, the chilled mirror dew point sensor in the AQUALAB 3 and AQUALAB 4TE is the fastest, and most accurate water activity meter available.

Do you need to grind the sample before placing it in the sample cup? or you could put the whole flower?

It’s advisable to measure bud which has been hand ground, broken up, or cut to expose the interior. When testing the whole bud, especially when case hardening occurs, you will likely have difficulty bringing the sample to full equilibrium in the chamber. After being stored in a closed container for a period of time, you will see more uniformity between the interior and exterior of the bud, and so after curing you might be ok testing whole bud. To be safe, exposing the interior of the bud during testing is best. Equilibrium will be achieved more quickly with smaller particles – so grinding with a hand grinder works very well.

If I over dry my bud, will a Boveda pack increase the weight?

Yes. The time and amount of Boveda needed is dependent upon the volume of over dry weed.

follow up for Brian on the increasing weight question- If you used a Boveda pack to increase weight, would this help increase the quality lost that occurred with over drying or increase potency?

Boveda will help protect and preserve cannabinoids from further evaporation when added to bud. No studies have been performed that show an increase in those cannabinoids when Boveda has been added.

What size sample is required for water activity of bud?

AQUALAB samples cups are 15 ml, and for cannabis flower, I recommend filling the cup about half full. It doesn’t need to be exact, but about 7 to 8 ml works well.

How many water activity samples should I take? For example 1000 kg batch.

This is a great question, and this is something you’ll need to experiment with. When taking random samples, how much variation are you seeing? How consistent is temperature and humidity where the cannabis flower is being stored. Depending on your circumstances, you can decide the number of measurements needed to adequately represent your batch.

Should I by chopping or milling a sample before measuring water activity in the laboratory? (Ambient relative humidity) Or just break up a bud with hands as you mentioned. Thank you.

We tend to recommend not using electric grinders because adding heat through friction can lead to water loss, thus changing the water activity of the ground sample. I’ve seen good agreement between breaking a bud into small pieces with gloved hands, and cutting with a knife or scissors. My favorite method for sample preparation, and the one which gives the fastest read times, is to use a small hand grinder. Ambient humidity does affect the outcome if the ground sample is exposed to ambient air for very long, so it’s best to prepare the sample just before testing in the AQUALAB. Or protect it by placing a lid over the sample if the sample is prepared in advance. If keeping a sample for more than an hour, it’s best to also seal the lidded sample with parafilm.

What is the best tool to measure moisture?

Because of the volatile content in cannabis flower, it’s very difficult to measure water content accurately. Water activity, on the other hand, is an easy non-destructive measurement. Because heat isn’t being added, volatiles like terpenes and flavonoids won’t evaporate during the testing process. Water activity is also a much more specific measurement, like measuring to the nearest millimeter rather than measuring to the nearest inch.

Models AQUALAB 3 or AQUALAB 4TE give the fastest and most accurate water activity measurements of all water activity meters. When a moisture model showing the relationship between water activity and moisture content has been added to an AQUALAB, both the water activity and the corresponding water content will be displayed. Based on my experience working with scientists at cannabis labs, the AQUALAB 3 and AQUALAB 4TE are the best.

Best tool to measure RH?

If measuring RH in a dry room, grow room, or curing room, it’s best to use a vapor pressure sensor. One that is rugged enough to be in and around the plants and at plant level. You’ll also want to have multiple sensors in each room in order to determine the vapor pressure deficit, temperature, and RH near and around the cannabis flower, and to find any inconsistency because of airflow issues. The ATMOS 14 is one example

Chilmere DuPont sensors?

The chilled mirror dew point sensor in the AQUALAB 3 or AQUALAB 4TE has the fastest and most accurate readings of all water activity meters. They also have the most stable calibration. If wanting to test the internal or equilibrium relative humidity – inside the bud – that’s the same as testing the water activity of the bud, and is different from testing the ambient RH in a room.

Will water activity affect the results of laboratory testing such as HPLC cannabinoid testing?

There are many factors which might affect the HPLC results. I’ve seen cannabinoid potency testing completed a couple of different ways. One method includes completely drying a sample till there’s no moisture left – then testing it in the HPLC for cannabinoid concentrations. But that concentration measurement is taken after all of the water has been removed and so a calculation must be made, based on water content, to determine cannabinoid concentration of the flower before it was dried.

There are many things that can go wrong in this process – the two major concerns are:

Has the sample being worked with in the lab lost moisture during shipping and sample handling, and if so will the calculation made using a moisture content value that really represents the rest of the batch.
Is the lab getting accurate and reliable moisture content results.
Many labs have switched to testing flower as received, rather than first drying it. I believe this is a better method for getting true values for potency.

If the question being asked is – will changing water activity change cannabinoid concentrations, the answer is yes. But it’s a little bit complicated. Inadequate storage conditions, over-dry flower, or under-dry flower, can lead to faster rates of potency loss over time. Water activity is the best way to maintain ideal moisture levels, and thus slow reaction rates (potency loss). Also, if cannabinoid concentrations are reported by %weight – changing moisture/aw levels will change the overall weight of the flower – thus changing the reported cannabinoid concentration.

How would you measure water activity in a Cannabis product that is in the finished product packaging?

It’s best to test product before it goes into packaging rather than after. And it’s best to have packaging which will adequately protect cannabis from ambient humidity. There are packaging equations, and we have software which automates the calculations, to determine if the packaging will protect the product throughout the desired shelf life, based on packaging permeability statistics provided by packaging manufacturers.

Once packaged, the package will need to be opened for a sample to be removed and tested, and then the package resealed or the contents repackaged.

What type of monitoring system for water activity would you recommend for the drying room ?

For testing water activity to ensure flower dries to ideal levels, I recommend an AQUALAB water activity meter equipped with a chilled mirror dew point sensor. They are robust, have faster measurements than other water activity meters, and are highly accurate.

It also helps to use ruggedized vapor pressure sensors, like the ATMOS 14, to monitor vapor pressure deficit, temperature, and humidity near and around the flower while it dries (as opposed to on the wall or hanging from the ceiling). Using multiple strategically placed sensors in the dry room will enable you to find inconsistencies and adjust airflow as needed, while also ensuring ideal overall humidity and temperature.

We are required to report potency and other analyses on a dry basis. We will need to know what the moisture content of the sample is. Will the METER analyzer give us this moisture concentration?

There are challenges when it comes to reporting concentrations on a dry basis – and then calculating potency using a moisture content measurement. There are a couple of reasons why.

If samples weren’t protected from ambient humidities during transport and prior to testing, they may not represent the batch as a whole.
It’s very difficult to measure moisture content in cannabis and hemp flower because of volatile content. Thus – the inaccuracy and lack of precision in moisture content testing can be a real problem.
Because of this, many labs have switched to testing potency in the flower sample as received. It might be worth starting a conversation with regulators in your state regarding this.

Having said that – yes, we can use a moisture model developed by the moisture sorption isotherm I presented in the presentation to determine water activity based off of a water activity readings. We can load a mathematical representation of the model into a water activity meter, and then with each water activity reading, the moisture content value will also be displayed.

When validating a testing method for water activity. Aside from running known standards, what are other tests performed to verify the reading of the water activity of the cannabis plant?

The first step is to validate that the water activity meter is working correctly – using certified water activity standards at various levels of water activity. This is generally done using salt solutions with known water activity to demonstrate that the meter test the salt standards within specifications. This is often referred to as the IQ/OQ. Some will follow the AOAC method for mixing saturated salt solutions (which are less accurate than unsaturated salt solutions but can be mixed yourself.) Saturated salt solutions are in a state between solid and solution (you will see many solid particles and liquids), and in this state the water activity is maintained – even without precisely measured components. If using saturated salts, you’ll need to add the potential inaccuracy of the salt to the inaccuracy of the meter you are using.

The 2nd step is to follow the guidelines of a formally published standard for testing cannabis flower – the ASTM D8196, for example – to ensure your sample handling and SOP are correct for your applications.

You can also send samples to an independent test lab. If doing this, it’s extremely important that you know the test lab is using proper procedures for sample handling, and that the sample is adequately packaged to avoid moisture exchange with the air. Auditing the test lab is a good idea. Even so, you will see some variation from one flower to the next – even when packaged together, so you will need to decide how much variation is acceptable.

As with every industry – like with cannabis, if a product is susceptible to changing water activity levels, it can’t be used as a standard itself. So, you can’t use cannabis flower, for example, as a standard. If you’d like to do additional comparisons using cannabis itself, for added reassurance, you can compare the same cannabis sample against other water activity meters, though, and with different types of sensors. If each of those meters and sensors read the salt standards correctly, you can test the cannabis flower (properly prepared and handled) in the different meters. Are the readings in agreement with each other within the accuracy of the meters? With dried cannabis flower, we see agreement across the different sensors, within the accuracy of the sensors being used. It’s important to note that with any water activity meter, cannabis will leave a sticky film over time and the chamber/sensor will need to be cleaned using IPA to avoid the effects of contaminants.

How would freezing cannabis affect water activity?

This is a really great question, and a difficult one because there are so many factors. Freezing any product will greatly lower the water activity – while it is frozen. Assuming the cannabis was in a vacuum sealed airtight package, and there has been no moisture movement during the freezing process or while in the frozen state, when brought back to room temperature, the water activity would presumably be the same as before freezing. This isn’t really practical, though, as freezing will cause water to move over time as the water crystal structures change – recrystallization. If this happens – after thawing you’ll likely have pockets of very high water activity where the ice has melted. The structure of the plant material also changes after freezing, and in cannabis it increases the rate of potency loss. How it’s packaged, the rate of freezing, the amount of time in the freezer, etc. all become factors.

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