Winterizing BHO means dissolving your crude butane hash oil in cold ethanol so that waxes, fats, and lipids precipitate out and can be filtered away. The result is a cleaner, more potent concentrate with better flavor. The process takes 24 to 48 hours (mostly hands-off freezer time) and requires only a few pieces of equipment.
Why Winterization Improves Your Extract
Butane extraction pulls cannabinoids and terpenes from plant material, but it also picks up plant waxes, lipids, and fats. These compounds cloud the appearance of your concentrate, mute the flavor, and make it harsher to consume. In vape cartridges especially, residual lipids can cause wicking problems and uneven heating.
Winterization exploits the fact that waxes and fats have higher melting points than cannabinoids and terpenes. When you dissolve crude BHO in ethanol and drop the temperature well below freezing, those lipids lose their solubility and clump together into visible particles. Cannabinoids and terpenes stay dissolved. You then filter out the solids, evaporate the ethanol, and you’re left with a purer oil that’s higher in cannabinoid concentration by weight.
What You Need
- 190-proof ethanol (non-denatured). Everclear is the most common choice. Lower-proof options contain water that interferes with the process.
- Mason jars with lids for mixing and freezing.
- A freezer. A standard kitchen freezer works, but a deep freezer that reaches below -20°C is better. The colder, the more wax precipitates out.
- Coffee filters or lab filter paper. For finer results, unbleached coffee filters work in a pinch, but a Buchner funnel with fritted glass in the 70 to 100 micron range gives a noticeably cleaner filtration.
- A Pyrex dish or silicone mat for evaporating the ethanol.
- A double boiler or hot plate (optional) to speed up evaporation safely.
Step-by-Step Process
1. Dissolve the BHO in Ethanol
Use a ratio of 10 mL of ethanol for every 1 gram of crude extract. Gently warm the ethanol to around 30 to 60°C to help the BHO dissolve completely, then stir until the mixture is uniform with no visible chunks. A mason jar works well for this. You want a fully homogeneous solution before it goes into the freezer.
2. Freeze the Mixture
Seal the jar and place it in the freezer. Leave it for at least 24 hours. Up to 48 hours is common and gives more complete precipitation. During this time, the waxes and fats lose solubility in the cold ethanol and form visible flakes, clouds, or a layer of sediment. The colder your freezer, the more thorough this separation will be.
One important detail: if your freezer stores anything else that could spark (older models with interior lights or auto-defrost elements), be aware that ethanol is flammable and its vapors are heavier than air. A sealed mason jar minimizes risk, but if you’re working at scale, a flammable-safe refrigerator or freezer is the proper equipment. More on safety below.
3. Filter the Solution
Remove the jar from the freezer and filter immediately, while everything is still cold. If the solution warms up, some of those precipitated waxes will redissolve and pass through your filter. Work quickly or pre-chill your filtration equipment.
Pour the mixture through your filter into a clean collection vessel. If you’re using a Buchner funnel with a vacuum flask, the process takes just a few minutes. With gravity filtration through coffee filters, expect it to take considerably longer. You may need to swap filters as they clog with waxy buildup. The liquid that passes through should look noticeably lighter and more translucent than what you started with. The yellowish or white residue trapped in the filter is the plant wax you’re removing.
Some people run the filtered liquid through a second clean filter for extra clarity. If you still see haze, you can return the filtered solution to the freezer for another 12 to 24 hours and filter again.
4. Evaporate the Ethanol
Pour the filtered solution into a wide, shallow Pyrex dish to maximize surface area. Ethanol evaporates at 78°C at normal atmospheric pressure, but you can speed things up at lower temperatures with gentle heat or a vacuum oven. If you’re using a vacuum oven pulling strong vacuum (around -28.5 inches of mercury), the boiling point of ethanol drops to just 12.8°C, which helps preserve heat-sensitive terpenes.
Without a vacuum oven, a warm water bath at around 50 to 60°C works. Let the ethanol evaporate in a well-ventilated area until only the oil remains. You’ll know it’s done when the surface stops bubbling and the extract has a stable, glassy or sappy consistency. A thin film of residual ethanol can linger, so give it extra time or a final gentle purge.
What Winterization Does to Terpenes
This is the trade-off. The ethanol soak and evaporation process inevitably strips some terpenes along with the waxes. Research on cold ethanol extraction found that terpene content varied dramatically with temperature: extractions at -40°C preserved roughly twice the terpene content compared to extractions at -20°C. Room-temperature processing fell somewhere in between, losing about 32% of terpenes relative to the -40°C baseline.
For winterization specifically, the ethanol evaporation step is where the biggest terpene losses happen, since many terpenes are volatile and evaporate alongside the solvent. Working at lower temperatures during evaporation (using vacuum rather than heat) helps preserve more of the flavor profile. If maximum terpene retention is your goal, some producers collect terpene fractions separately and reintroduce them after purging.
Safety Considerations
Ethanol ignites at normal room temperatures, and its vapors are heavier than air. This means fumes settle toward the floor rather than dispersing upward. Oregon OSHA guidelines for cannabis processors require exhaust ventilation within 12 inches of floor level in any room where ethanol is used, with enough airflow to cycle the room’s air volume six times per hour.
At home scale, this translates to simple precautions: work in a well-ventilated area, ideally near an open window with a fan directing airflow out. Never evaporate ethanol near open flames, gas stoves, pilot lights, or sparking appliances. Use an electric hot plate rather than a gas burner. Keep ethanol containers sealed when not actively pouring, and store them away from heat sources.
If you’re storing ethanol in a freezer, it needs to be a flammable-safe unit with no interior ignition sources. Standard household freezers sometimes have interior lights or defrost heaters that could theoretically ignite ethanol vapor from a leaking container. At small batch sizes with a tightly sealed mason jar, the practical risk is very low, but it’s worth understanding why commercial operations use explosion-proof equipment.
Tips for Better Results
Pre-chill your ethanol in the freezer before mixing it with the BHO. Starting cold means less time waiting for waxes to precipitate. Some people keep a dedicated bottle of Everclear in the freezer at all times for this purpose.
If your first filtration pass still leaves a hazy product, a second winterization cycle will catch more. Dissolve the filtered oil back into fresh cold ethanol at the same 10:1 ratio, freeze again for 24 hours, and filter again. Diminishing returns kick in after two rounds, but a double pass can make a noticeable difference in clarity and smoothness.
The waxy filter cake left behind still contains small amounts of cannabinoids. It’s not worth trying to recover them at home scale, but it’s normal for winterization to cost you 5 to 20% of your starting weight in removed material, depending on how lipid-heavy your crude extract was.