Water Content In Cannabis Testing

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How does water content affect your test results?

One of the things that can affect the test results of cannabis is the water content of the flower. When we test for THC and other cannabinoids, we express the results in the form of a percent. Let's say that a flower tests at 18% THC. That means that if you have 100g of flower you should have 18g of THC. That is, of course, assuming that all buds have exactly the same THC content, which they don’t. We will discuss variability in another article. For now, we are assuming that THC content is consistent throughout the batch. 

The equation we use is this:


What does this have to do with water content? Well, water content is the thing that can change the most. Let's say you have a bag of buds. The amount of leaves, stems, THC, CBG etc.. is fixed for the most part. But, if you were to dry out that bag it would weigh less. Or the opposite, if you add moisture back into the bag it will weigh more. You haven't changed the amount of plant material or cannabinoids but you have changed the weight just by changing the moisture content. 


So let's think about that for a minute. That means that if the actual THC content stays the same and you increase the weight - you decrease the percentage THC. It also means that by drying out your buds - you increase your percentage of THC. Understanding this relationship is important for everyone in this industry. Growers, extractors, processors, labs, retailers and consumers can all be affected by this. 

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The ideal situation would be if all cannabis was sold, processed and tested at the same moisture content. However, this is clearly not the case. There are companies, like Boveda, that make products to control the moisture in the curing and storing process. Yet, even these companies offer products with varying levels of humidity for people to choose from. There is no industry standard. To further complicate the situation, some labs desiccate (remove all water) their material to attempt to control their results while others do not. This is not ideal either. Heating the flower to dry it out can cause cannabinoids to degrade or change. Also, cannabis is not typically sold or consumed completely dry so the lab results wont reflect the actual product on the shelf.

Many labs are moving to testing “as received.” This will give the results that best reflect the product that reaches a consumer. Companies submitting samples are encouraged to submit samples cured and dried to the moisture content that they intend to sell the product at. This will ensure that you get the most accurate test results. 


Moisture Content Vs. Relative Humidity

Moisture content and relative humidity are related but are totally different things. Lets explore the difference.

Moisture content is the amount of water that is trapped inside the plant material. The simplest way to determine the moisture content would be to weigh a portion of buds, then dry them out completely and weigh them again. The difference is the weight of the water that was trapped inside. You then divide the weight of the water by the wet weight. There are also meters that can measure moisture content to varying degrees of accuracy. When alive, cannabis has a moisture content of about 80% it will begin to crumble at a moisture content around 9%. Ideal storage is considered 10% - 15% moisture. 

Relative humidity is essentially a measure of the moisture content of the air. There is a complex relationship between relative humidity and moisture content. I won’t get into the equation. When the cannabis comes in contact with air for a period of time, it reaches an equilibrium. If the relative humidity goes up the moisture content will go up and conversely, if the relative humidity goes down the moisture content of the buds will go down. The amounts are different though. 

What does this mean for me?


Make sure you prepare your product the same way for all of your samples. Control humidity in curing and drying containers. Use a hygrometer to maintain the relative humidity of your drying room. Store your product to ensure consistent moisture content. This can be done by using moisture exchange packets like Boveda or by simply using airtight containers after you have ensured your target moisture content. Always make sure it is stored below 15% moisture content to discourage the growth of microorganisms. 


You are typically concerned with the actual amount of THC or other cannabinoids in the product you buy. Many extractors buy based on grams or Kilograms of THC. This means that you need to control for moisture content when you are buying quantities for extraction. It is best to have the product tested yourself at the moisture content you are buying it. That way you can ensure that the sample was not excessively dried prior to testing


Just like extractors, you need to make sure that the label you put on your product is what the consumer is receiving. Make sure you trust your supplier or, better yet, have it tested yourself. You should make sure you sell it at the same moisture content it was tested at. 


Buying from a reputable supplier is very important. The best suppliers will test every batch and label it accordingly. Many suppliers will also have it tested for contaminants such as mold, heavy metals, and pesticides. In Maine, this will be a requirement for all products sold under the adult use program. Many caregivers are doing this already.

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