4 Tips for Managing Post-Harvest Humidity in Cannabis From Solstice

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‘Cold and Controlled’ is the motto at Seattle-based Solstice.

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February 8, 2021

Terpene preservation starts before harvest at Solstice to ensure the final product retains its fragrance and flavor.
Photo courtesy of Solstice

At Solstice, preserving terpenes through the post-harvest process begins a day before harvest, when the cannabis cultivator reduces temperatures in its indoor and greenhouse flower rooms just before plucking fresh buds. Outside, the team wears headlamps so they can harvest before sunrise when temperatures are cooler, says Craig Allen, inventory manager at Solstice.

In indoor and greenhouse rooms, managing humidity throughout growing and during the drying and curing stages is key to retaining the flower's flavor and fragrance. Here, Allen shares how the Seattle-based company controls the climate in its drying and curing spaces to protect delicate terpenes.

1. Develop standard operating procedures (SOPs) for preserving terpenes.

Solstice calls its terpene preservation plan the "Cold Train,” Allen says, and it details temperature, humidity and more from the day before harvest through drying and curing to be sure the plant is protected at every step.

“We try to not let anything heat up so we have terpene preservation throughout the entire ‘Cold Train,’” Allen says, adding they keep the temperature below 62°F. “If you’re able to smell the cannabis product, those are terpenes leaving the product itself, so the goal is to keep it cold and controlled and not handle the product very much.”

2. Control both the climate and individual microclimates using monitors.

Keeping the “Cold Train” on schedule depends on precise environmental controls. Solstice has a separate HVAC system in its curing and storage space so it can carefully control temperature and humidity. The company also installs hygrometers throughout the facility—in each corner of the room, within individual bags and totes—so they can monitor overall room environment, relative humidity and individual microclimates, Allen says.

“The ability to control the microclimates within our bags or jars [and] also being able to control the entire environment of the room” is essential, he says. “If the room is too humid for the jars to burp, you’re not able to properly cure the product. … You’re going to want to have the room at lighter humidity so it can wick out ... [of] the product into the environment.”

Monitoring conditions just outside of the curing space is just as important as inside, Allen adds.

“If we leave the door open too long, it’s going to change the room in general,” he says, adding that hygrometers are also placed to measure conditions outside of the curing space. “Knowledge is power; the more monitors [you have] gets you to statistically understand your space.”

3. Vary drying humidity.

It’s important to vary humidity in drying, Allen says. “We are more aggressive about removing humidity from the air at the beginning of the dry process and then really taper off and slow down the dry toward the end,” he says. “You don’t want cannabis to sit in a high humidity environment because you have potential mold problems.”

The team aims for a 10-day dry, Allen says, prolonging the step as long as possible to achieve optimal terpene preservation.

“We adjust the controls so we keep [the dry] low and transitional [temperature and humidity] levels,” he says. “We don’t want anything jarring.”

4. Keep curing humidity consistent.

Once product is dried, Solstice aims for a consistent 55% humidity in its curing space, Allen says.

“We take big influxes of product at different moments, so monitoring that room is key to keep things curing at a proper rate,” Allen says, adding that the extra product can boost humidity quickly. “We’ve really got to crank up the [dehumidifier] and dial in the room environment. This is commercial scale, big-time growing and curing."

Michelle Simakis is editor of Cannabis Business Times.