Homegrown with Jim Berry: Drying and Curing Cannabis

Think of a sponge. If you were to fully saturate it with water, that sponge would weigh more and have a very high moisture content, maybe 95%. Now wring out that sponge. It’s the same sponge and the same volume, but now it weighs much less, as it holds much less water. It has a much lower moisture content—maybe 40%. If you were to throw that sponge in a warm oven and let all of the water evaporate, it would have 0% moisture content.

Most quality flower will fall between 10% and 12% water. But the moisture content of flower is kind of a useless metric—water activity is of much more concern. Water activity is representative of how available internal water is for other activities.

Refer back to the sponge: think of water activity as “how hard you have to squeeze that sponge to release the water.” A completely saturated sponge requires a little squeeze to release water. Once it has been thoroughly wrung out, the sponge is still wet, but it is very difficult to squeeze more water from it. That water is essentially bound to the sponge.

It is the availability of unbound water that is so critical to optimal success. The goal is to get the water activity low enough, quickly enough, that there is no available water for microbes to live and reproduce. If you don’t dry your flower enough, or if you dry it too slowly, you are giving fungi the opportunity to thrive inside your flower.

I don’t want to alarm you, but you’re probably breathing in a few active mold spores while you read this. They are ubiquitous. However, if those spores are allowed to take hold and thrive, within a couple of days, all of your hard work could be turned into a moldy mess that’s not safe to smoke.

Fortunately, science and the food industry have long since determined that threshold of water activity: 0.6 active water, or in practical terms, 60% relative humidity. At or below this threshold, microbes are unable to propagate. The flower is now shelf-stable.

Coincidentally, it’s also at about that water activity that you’ll be able to keep the joint lit. (And the ash should be white).

Am I Drying or Curing Cannabis?

Most of what we have considered drying and curing is really just about stabilizing and maintaining proper water activity. This is where most SOPs start to slip, because the goal is not only to get the flower to the proper water activity, but to keep it there. This is when most of the actual “curing” happens.

We are just beginning to realize all of the secondary metabolites present in cannabis, their role in both the plant’s biological process and our consumption experience. We’ve identified cannabinoids, terpenes, flavonoids, thiols, esters, and sugars, just to name a few.

Long after the flower has been harvested and dried, there are still enzymatic activities happening that will mature the flower. And what element do those enzymes rely on in order to do the job? Water.

If you overdry your flower, those enzymatic processes slow or completely halt. It’s why weed that was dried too much or too fast is often harsh and flavorless.

Most of the good stuff that we seek is encapsulated inside the trichome head. The thickness of the wall of that head is only two cells deep. When the room is too dry and the vapor pressure is too high, more of those heads will burst. Among the good stuff inside those heads are terpenes and thiols, both known as volatile organic compounds. When the heads burst, those compounds evaporate right into the room.

As I’ve said for years, “If you’re smelling terps, you’re losing terps.” The same goes for thiols, or volatile sulfur compounds (VOCs), those responsible for a lot of gas, diesel, skunk, and garlic.

What is the best way to retain those VOCs when drying cannabis? Low and slow. You want to select a cool, dark place with a little air circulation. Temperatures in the 60s are good. Pick a space where you can control the RH (relative humidity) with a humidifier and a dehumidifier. Choose set points on that equipment that keep your RH as close to 60% as possible, without having the two working against each other.

The sensors on most consumer equipment are not very accurate, and the two certainly won’t be in tune. You may have to play with the settings on each until the space stays within as tight a range as possible. The wider the swing in your humidity throughout the cycle, the more vapor pressure fluctuations the space will have, and ultimately, the more trichomes you will lose to ruptured heads.

It is also important to keep that space clean. Especially early in the drying process, there is plenty of water activity available for opportunistic spores flying around the room to settle into your flower and ruin it.

Next: the Containers

With diligence and a little good fortune, in about 10-12 days, the flower will be ready to be picked from the stalks and put into small air-tight containers. If the small stems bend a little before they snap, your flower is probably pretty close to dry.

At this point, your flower may be dry enough on the outside, but still have excess moisture trapped in the middle. Fill your containers about 70% full, allowing a 30% air gap at the top. Take a couple of minutes each day to “burp” your containers. Opening each container daily will allow for a little humidity and gas exchange. You are working to get each container stabilized at 0.6 water activity, or 60% RH. I recommend picking up a small hygrometer/thermometer that will fit in your container to measure the humidity.

Once your flower is properly dried and water stable, the actual curing happens. Carbohydrates are breaking down into sugars, chlorophyll is breaking down, esters are being formed, just to name a few activities. We are just beginning to understand all of the processes still happening in the flower at this point.

Each cure is completely dependent on strain and personal preference. Some flower may smoke remarkably well right after the drying process, and some may sit for six months before it’s just the way you like it. It’s really between you and your genetics. The most important factor is maintaining the proper water activity the whole time.