How to Fresh-Freeze Cannabis

Question: Hi, I keep reading articles and social media posts about freezing freshly harvested buds to preserve freshness, minimize mold and mildew contamination, and lower production costs.

I recently took a few dozen branches from freshly harvested plants and placed them into a walk-in freezer. When I checked on them a few days later, they had basically turned into a frozen mass covered in ice on the surface.

Can you please explain why and how to freeze, and how this can lower my cost of production? I would certainly like to lower costs, but I'm also very curious about how I can utilize this process as a means of storing my excess cannabis and minimizing its degradation. Also, what is frozen cannabis best utilized for?

Answer: It’s true enough that more and more growers are freezing cannabis flower destined for specific types of extracts. Live resin and live rosin extracts, in particular, are made using fresh-frozen cannabis. Both heat and oxygen are primarily responsible for terpene loss and THC degradation. This method minimizes exposure and preserves the most terpenes possible.

Cannabis buds yield a plethora of terpenes, which are volatile, resulting in a large percentage of these terpenes evaporating during harvesting, drying, and/or curing (see The Volatile Oil Composition of Fresh and Air-Dried Buds of Cannabis sativa” by Samir A. Ross and Mahmoud A. ElSohly). Freezing the freshly harvested buds immediately after harvest solidifies the chemical contents in the trichome heads, thus minimizing losses from evaporation. In a proper sub-zero environment, fresh-frozen cannabis will maintain freshness and quality for over a year.

Another advantage of fresh-freezing cannabis is that the amount of time between harvest to processing is minimized. The resulting extracts have a much longer shelf life than cannabis buds. Freezing cannabis also helps solidify unwanted compounds such as wax and fats, which are then easier to filter or remove from a hydrocarbon extraction.

A rapid transition from harvest to frozen can also minimize the growth and proliferation of bacteria and molds that can contaminate the buds during hang-drying and curing. By not drying and curing the cannabis, growers can minimize the duration of the post-harvest phase and can avoid having to purchase and operate expensive environmental control equipment to maintain dry and cure rooms.

(Editor’s note: Fresh-freezing is a completely different process from freeze-drying, which is used for consumable flower products. For more on freeze-drying, see this video interview with Buckeye Relief’s team.)

How to Fresh-Freeze Cannabis

The key to fresh-freezing cannabis is to limit the buds' exposure to room temperatures after harvest. Additionally, if unsealed containers are placed in a conventional non-sub-zero freezer, ice crystals can form on the outer surface of buds. This ice can inhibit the extraction process, resulting in a minimized yield of extract, as well as potency, aroma, and flavor.

Here are the steps to follow to properly fresh-freeze your cannabis:

1. Remove all fan leaves and secondary leaves without trichomes.
2. Remove branches and trim/buck off the buds.
   1. Do a second pass to remove all leaves without trichomes.
3. Immediately place the harvested buds into insulated coolers with dry ice (never allow the buds to make contact with the dry ice) to precool the buds.
4. Trim the buds.
   1. It is best to work with buds in cold temperatures.
5. Place trimmed buds into sealable moisture-resistant bags or containers, and place the containers into another cooler with dry ice.
   1. Many growers prefer to precool the buds utilizing dry ice so that they will be below 65°F (18°C) prior to placing them into the blast freezer or freeze tunnel. These rapid freeze processes minimize the formation of ice crystals.
   2. Under perfect conditions, you want the buds to be in the 32°F to -4°F range (zero to -20°C) on the surface of the buds, and preferably within that same range inside the larger buds before rapid freezing.
6. Lightly vacuum seal the containers that contain the trimmed buds.
   1. Do so gently; do not clump it all together. Layer the buds so there is a loose to medium consistency, and so they are fairly flat to better facilitate the blast freezer. This minimizes freezing time while ensuring even freezing throughout the contents. Vacuum sealing also minimizes oxidation and ensures outside moisture does not migrate to the buds and form surface ice.
7. Place vacuum-sealed containers into a third cooler with dry ice.
   1. It is imperative that the frozen cannabis is never allowed to thaw before it is utilized for extraction.
8. When the third cooler is full, place the containers into the blast freezer or freeze tunnel to be frozen.
9. After blast freezing, place the frozen buds into a sub-zero freezer capable of achieving at least 0°F (-18°C), but preferably, buds should be stored at -4°F to -22°F (-20°C to -30°C). Some growers prefer as low as -40°F to -112°F (-40°C to -80°C).

Fresh-frozen cannabis is a benefit to both consumers and growers because freezing the cannabis minimizes labor costs and reduces the time between harvest, extraction, and processing. A grower can simply harvest, trim, and freeze a harvest, rather than harvest, trim, dry, and cure. When fresh-freezing, the frozen buds are ready for extraction or delivery to the extraction facility only 24 hours after harvest. This results in a lower cost of production of the starting material, and ultimately a lower price for the resulting extract, allowing for a lower price to customers.

Things to Avoid When Fresh-Freezing Cannabis

Frozen trichomes are hard and brittle. Excessive or rough handling of frozen cannabis can damage and dislodge trichomes, thus diminishing potency and flavor. Do not drop or shake frozen cannabis bags.

Look for leaks or holes in containers. Any leaks can result in trichome loss or freezer burn if not under vacuum. Freezer burn causes cellular damage, resulting in terpene compromise, cannabinoid degradation, and discoloration.

Never allow buds to thaw before use; only remove them from the freezer as needed for use in extraction. Letting them thaw allows terpenes to evaporate, and it’s better for the extraction process if the buds are frozen, not thawed.

You must be mindful that the reason for freezing is to best preserve the desired compounds. As such, timing is very important: If you do not arrest terpene loss by immediately solidifying the trichome head by utilizing insulated coolers and dry ice at all trim stations, pre-blast freezer steps, and when utilizing a freeze tunnel, all these steps are meaningless. As the cannabis sits, it wilts and loses the qualities you are attempting to preserve.

Kenneth Morrow is an award-winning grower and breeder. He is the owner of Trichome Technologies, a research and development company. He is also a consultant and author of the book "Marijuana Horticulture Fundamentals" and a founding advisory board member of Cannabis Business Times, where he has been a columnist since 2015. Find him on Instagram @trichometechnologies or reach him via email at: [email protected].