Treatise on the Decarboxylation of Cannabinoids
Decarboxylation is a process in which carbon dioxide (CO2) leaves a stable molecule and floats off as a gas. Atoms in a molecule can be thought of like billiard balls, with each one having a size, weight, and exact position. As these atoms float away, the substance left behind will become lighter, like a dry towel being lighter than that same towel soaking wet. The idea is that as the CO2 leaves, the weight left behind is reduced.
As we can see in the illustration, the weight of the CO2 is lost as it floats away, leaving less mass and weight of substance than before decarboxylation occurred. Decarboxylation typically occurs when a substance is heated, but it can also be caused by exposure to certain frequencies of light, and catalyzed by certain substances like molecular oxygen in the air.
If the weight of the molecule before and after its decarboxylation is known, then a percent of mass lost in decarboxylation can be calculated. If the CO2 contributes 10% of the weight of a molecule, than 90% of the mass remains after decarboxylation. This would mean that continuously heating 100 g of this substance would eventually yield 90 g of the decarboxylated substance, as the remaining 10 g represent the weight of CO2 which gassed off.
How does decarboxylation effect cannabinoids?
Cannabis only has the ability to produce cannabinoid acids, like THCA and CBDA. THC is only created when the buds are decarboxylated outside the plant. This decarboxylation is usually achieved by the heat of fire when smoked, or from the heat of baking in edibles. Most cannabinoids lose approximately 12.3% of their mass upon decarboxylation. That means that if you had 100g of crystalline isolate of a cannabinoid acid, such as THCA, after decarboxylation you would have 87.7 grams left of THC.
This knowledge is important for people decarboxylating cannabinoids by themselves, particularly producers of cannabis-infused edible products and hash oil producers that wish to sell decarboxylated oil. This is also important for brokers of raw cannabis products such as cured cannabis flower, who must either report the value of the cannabinoid acid directly observed by the testing lab, use the theoretical conversion, or display both.
The labeling issue with raw flower is not as easy as it seems at first glance. Let’s consider a typical example of THC-dominant cannabis. A lab will test the flower and find 26% THCA and 3% THC. 3% THC occurs because a small amount of the cannabinoid acids are decarboxylated by air and sun before harvesting and curing. The smaller amount of THC observed directly by the lab typically indicates that the cultivator has submitted fresh cannabis that has been protected from light and exposure. A higher THC content indicates that the cannabis flower has undergone more exposure and is therefore not as fresh as flower with a low THC content.
Now a broker or dispensary has a choice to advertise certain numbers: 26% and 3% from lab testing, a theoretically calculated number of 25.8% THC, or both sets of numbers. Providing the patient with both sets of numbers gives them the greatest amount of information, while also reducing liability on the cannabis business involved in label making. Sample calculations are provided below:
[Decarboxylation of THCA Only]
26% THCAobserved x 0.877 = 22.8% THCtheoretical
[Total Sum of THC]
22.8% THCtheoretical + 3% THCobserved = 25.8% THCmaximum
(26% THCAobserved x 0.877) + 3% THCobserved = 25.8% THCmaximum
It is important to note that the mass loss is not a conversion rate. Mass loss assumes that all of a substance will decarboxylate and calculates how the mass will change. An accurate answer must account for how much of the cannabinoid will decarboxylate. Studies indicate that 30-70% of cannabinoids undergo decarboxylation under standard smoking conditions. This is why our calculations at Digamma are only a theoretical maximum, and are not a result with the same standing as those directly observed in the plant. This is also why it can be very important to label your theoretical calculations as such, and provide all original values provided by lab results, as a means of reducing liability upon your business.
Author's Note: Common naming systems used in California, Colorado, Massachusetts, Nevada, Oregon, and Washington for the maximum calculated THC are “total THC” “potential THC” and “maximum THC”, though one naming scheme has not emerged as the industry standard yet.
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About the Author
Marco Troiani is one of the founding members of Digamma Consulting and the laboratory manager. He was also the laboratory manager of DB Labs from its founding 2015-2016. His responsibilities included developing detection methods for terpenes and solvents (GC-MS), metals (ICP-MS), pesticides (GC-MS-MS), and Total Yeast and Mold, Total Aerobic Bacteria, Total Coliform Bacteria, and Salmonella spp. in cannabis and associated products.