What Is Ice Nucleation in Fresh Frozen Cannabis?

Todde Philips   

🇺🇸 Retired veteran, father, rock-climbing expert & rosin connoisseur

Like humans, living cannabis plants are composed mostly of water. At around 80% of their total weight, water accounts for the bulk of a cannabis plant’s biomass. After harvest, water slowly evaporates during the drying and curing process. But cannabis doesn’t have to be air dried in preparation for hash production.

Fresh frozen cannabis has become the predominant source material for creating bubble hash and hash rosin. Freezing cannabis immediately after harvest allows us to capture and preserve the high terpene content that’s present in the living plant, which translates into explosive flavor profiles for the consumer to enjoy. 

Water in its liquid form facilitates a variety of functions within the living plant. But what happens when we freeze the water immediately after harvesting? Freezing fresh cannabis material causes ice nucleation to occur inside the plant, a natural consequence of the phase change of water.



What Is Ice Nucleation?

Ice nucleation refers to the formation of ice crystals in fresh frozen cannabis material. It’s a natural process that can’t be prevented, but potentially negative effects on the hash washing process can be managed. 

Ice nucleation occurs when water inside of fresh frozen cannabis forms small ice crystals along plant cell membranes. Because ice has a higher volume than water, once water inside the plant freezes it expands. These ice crystals rupture the cell membranes and effectively damage plant tissue from the inside out. Think of the results like an explosion of chlorophyll within the plant. 


Once the inner workings of the plant’s circulation system is damaged, chlorophyll can easily spread throughout the plant biomass, once it’s thawed. However, as long as the material remains frozen, the chlorophyll will remain in place.  



Only when the ice crystals melt is the chlorophyll free to leak out of the plant material. This means that if the material is allowed to completely thaw out while washing it for hash, the chlorophyll can easily contaminate the water. 

To summarize, ice nucleation releases chlorophyll from its confinement within the plant tissue, while the thawing of those crystals allows the chlorophyll to mobilize. Once mobilized, it will inevitably bleed out into the hash water. Unlike small pieces of plant matter or even trichome stalks, the chlorophyll in this form is difficult to thoroughly filter out of the water. 

How To Minimize Chlorophyll Contamination



Ice nucleation in fresh frozen cannabis is inevitable, but an overabundance of chlorophyll contamination isn’t. As the material warms, the chlorophyll will more readily be released, so the key is to keep the material as cold as possible and avoid letting it thaw. 


Ways to keep the water super cold and the fresh frozen material in a nearly-frozen state include using insulation around your work bucket or agitator, working in a cold room, and adding the right amount of ice (without overcrowding). 

Ice is critical to keeping the cannabis and water at the ideal temperatures, but it can also reduce the power of the water’s vortex while mixing. The right amount of ice will keep everything cold while still enabling the free-flow and vortex effect of water in the mixer. 

Working efficiently and moving quickly is key. The goal is to sieve the resin from the water in as little time as possible. 

Another way to minimize the effects of ice nucleation is washing hash in a room with temperatures below 50 degrees Fahrenheit. This cold room temperature helps to keep the water cold and slows down the rate at which the fresh frozen cannabis will thaw. 

Water chillers are another piece of equipment that can help keep the fresh frozen cannabis frozen for longer. As long as the material stays frozen, the chlorophyll from ice nucleation remains locked inside. 

All that said, it’s still possible to release excessive chlorophyll if the wash is too aggressive, lasts too long, or the same batch of material is overworked with too many washes. 


The same principles that guide any ice extraction will serve you well in minimizing the effects of ice nucleation. Keep the water as cold as possible without (overcrowding the mixer with ice), work quickly in a cold room, and use an insulator around the mixer or washing machine. 

Ice nucleation can’t be avoided, but it doesn’t have to ruin your washes. Now that you know the downside of allowing fresh frozen material to thaw, you can work that much harder to keep everything cold. 




What is ice nucleation?
Ice nucleation refers to the formation of ice crystals in fresh frozen cannabis material. These ice crystals rupture the cell membranes and effectively damage plant tissue from the inside out. 

Can you prevent ice nucleation from occurring?
Ice nucleation will always occur within fresh frozen cannabis material. If you don't want to combat the effects of ice nucleation, using air dried cannabis for hash production is another option. 

How can you keep fresh frozen material from bleeding chlorophyll into your hash?
In short, by keeping everything cold! The water should be as close to freezing as possible. Work in a cold room. And wash and sieve the fresh frozen material as quickly as possible. 

How can you remove chlorophyll when washing hash?
If ice nucleation is the source of the chlorophyll contamination, it's very difficult to remove it with the ice water extraction process. Rinsing the hash thoroughly before collecting it from the wash bag screens is the best approach, but won't remove all chlorophyll. 

How cold should the water be when washing hash?
The water should be kept in the low 30-degree Fahrenheit range when washing hash. 



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