Am I measuring the THC per serving in my marijuana brownies correctly?

Hey, Cannabist!
I cook up 15 grams of trim in coconut oil, and my flower tests between 12 percent to 15 percent THC. If I make brownies in a 13 x 9-inch pan and cut them into 10 servings instead of 18 (like the brownie mix says), do I have 15 milligrams THC in each slice or 150 milligrams? Please help, thanks in advance!
— Kitchen Chemist

Hey, Kitchen Chemist!
What’s cooking? I’m glad you’re double-checking the THC per serving in your pot brownies. There’s a big difference between 15 milligrams THC and 150 milligrams THC per serving … and by my math your numbers are off target. I compute your THC per serving to be 180 milligrams or 225 milligrams per serving, depending on the THC potency of your flower. Either way, that’s a super-potent end result.

It’s important to get the marijuana math part straight in any mouthwatering homemade brownie recipe, so let’s walk through the numbers together. To corroborate the calculations, I asked Jessica Catalano, Colorado-based cannabis chef and author of “The Ganja Kitchen Revolution,” to join us. It’s also worth noting that there are other factors in play with the potency of homemade cannabis oil and these are only approximations. For example: Was the trim decarboxylated to activate the THC before it was used to make the coconut oil? (Keep reading for more info.) Also, we’ll presume that the entire amount of coconut oil you infused went into this one particular brownie batch.

First of all, it’s great you have analytical reports for THC potency of the trim. It’s best to have as accurate THC potency numbers as are available to calculate the THC content of anything you cook up with cannabis. When you know the strain of flower or trim but don’t have analytical test reports for the plant material being used, you can gather potency numbers from strain databases and websites. Otherwise, start with a (very) general estimate of 10 percent THC content for the plant material you’re using in the recipe.

Here are the basic calculations:
Step 1: Determine the dry-weight amount of THC for the cannabis used in the recipe.
Step 2 formula: Dry-weight amount of THC (in milligrams) divided by recipe yield = THC milligrams per serving

Let’s start our calculations with an easy conversion to remember: 1 gram of cannabis has 1,000 milligrams dry weight.

Now, calculate the THC potency by taking the total dry weight of marijuana being used in the recipe and multiplying it by the potency percentage.

For example, if 1 gram (1,000 milligrams) of cannabis has 10 percent (.10) THC, then:

1,000 x .10 = 100 milligrams THC

So, 10 percent of 1,000 milligrams would be 100 milligrams THC. Got that?

Let’s return to your brownie batch by converting the total grams of cannabis in the recipe to milligrams of dry weight. In your case, 15 grams converts to 15,000 milligrams.

Next, multiply the total dry weight (in milligrams) of cannabis by the THC potency percentage to get the THC content in the whole batch of brownies. Based on your note about potency variance of 12-15 percent, we’ll look at both the lower and upper figures:

If the trim has 12 percent THC potency, the 15,000 milligrams of cannabis in the brownie recipe contains 1,800 milligrams THC.

15,000 x .12 = 1,800 milligrams THC dry weight

To tally the dosage per individual serving, divide the amount of dry-weight THC (in milligrams) by the total servings for the pan of brownies. If you cut your brownies into 10 generous servings, 1,800 milligrams divided by 10 means each portion has 180 milligrams THC.

1,800 milligrams / 10 = 180 milligrams THC

If the brownies are cut into the original suggested size of 18 portions, 1,800 milligrams THC divided by 18 portions, then each brownie has 100 milligrams THC.

1,800 milligrams / 18 = 100 milligrams THC per serving

Now, let’s calculate the 15 percent THC potency for your brownie recipe.

The dry weight is still 15,000 milligrams of cannabis in the recipe.  If you multiply 15,000 milligrams by 15 percent THC potency, that’s 2,250 milligrams THC in the brownie batch.

15,000 milligrams x .15 = 2,250 milligrams THC

When cutting the single servings, divide the total THC content, 2,250 milligrams, by the number of servings. Sliced into 10 big pieces, each brownie would have 225 milligrams THC per serving. If the pan of brownies is divided into 18 sections, each brownie would have 125 milligrams THC per serving.

That answers your immediate dosing question IF you prepped the cannabis correctly. As Catalano points out via email, “It is absolutely important to note that if the cannabis bud was not fully activated at the right temperature and time, then milligrams of THC are going to fluctuate dramatically.”

Activating cannabis flower or trim with heat transforms the non-intoxicating THCA cannabinoids into psychoactive THC, a process known as decarboxylation — it’s what happens when you light a joint or vaporize flower. The basic idea on preparation for cooking is to apply low heat for a short time to convert the THCA into THC. Catalano recommends heating cannabis to 225 degrees for 25 minutes.

Catalano adds: “If the coconut oil was overcooked, then milligrams of THC are going to fluctuate dramatically.”  The best way to prevent overcooking is to monitor the temperature of the coconut oil when you are infusing it with cannabis and not exceed the smoke point of coconut oil, which is 350 degrees. For more info, check out this previous Ask The Cannabist column, “Cannabutter recipe debate — to use water, or not?

As you can see, there are a lot of variables that factor in, so THC calculations for homemade edibles essentially are a rough estimate.

Before you get back to baking, one final note about dosing. It may be your intention to make high-potency brownies for medical purposes — or it’s your personal preference. However, if you’re sharing your brownies with other adults in a recreational setting, I recommend using less cannabis in the recipe to lower the THC dosage per brownie so that nobody will be surprised by your potent pot brownies. Or cut them into smaller servings: In Colorado, the standard serving size for a commercially made edible is 10 milligrams THC. XO

Ask The Cannabist: Clearly you have questions about marijuana, be it a legal concern, a health curiosity or something more far-reaching. Email your queries to askthecannabist@gmail.com.

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