BHO extraction is a method of making cannabis concentrates by using liquid butane as a solvent to strip cannabinoids and terpenes from plant material. The result is a potent oil that typically contains around 75% THC, with extraction yields averaging about 12% of the starting plant material’s weight. It’s one of the most common techniques in the cannabis concentrate industry, producing products sold as shatter, wax, budder, and live resin.
How Butane Extracts Cannabinoids
The active compounds in cannabis live in tiny, mushroom-shaped glands called trichomes that coat the surface of flowers and leaves. The oils inside these trichomes are hydrophobic, meaning they don’t dissolve in water but dissolve readily in non-polar solvents like butane. When liquid butane passes through raw cannabis material, it strips these trichome oils away from the solid plant matter, carrying the dissolved cannabinoids and terpenes with it through a filter.
This selectivity is what makes butane effective. It pulls out the compounds people want (THC, CBD, terpenes responsible for flavor and aroma) while leaving behind most of the chlorophyll, cellulose, and other plant solids. The filtered solution of butane and dissolved cannabis oils then needs to have the butane removed, leaving behind the concentrated extract.
Open Blasting vs. Closed-Loop Systems
There are two fundamentally different setups for running a butane extraction, and the gap between them is enormous in terms of safety.
Open blasting uses an unsealed tube packed with cannabis. Liquid butane is pushed through one end, and the solution drips out the other into an open container. The butane then evaporates into the surrounding air. Because butane gas is heavier than air and extremely flammable, this method has caused countless explosions and fires. It’s illegal in regulated markets for good reason.
Closed-loop systems keep the entire process sealed from the outside environment. Butane never contacts open air. It flows from a pressurized tank through the plant material, collects in a sealed vessel, and is then recovered and recycled back into the system. This eliminates the explosion risk from escaping gas, reduces solvent waste since the butane is reused, and allows the process to run at higher pressures and temperatures for faster, more efficient extraction.
Commercial Safety Requirements
Licensed extraction facilities operate inside specially engineered rooms classified as C1D1 (Class 1, Division 1) environments. These rooms are designed around one principle: never allow a spark in a space where flammable vapors could accumulate.
The ventilation system maintains a minimum airflow speed of 100 linear feet per minute across the workspace, pulling any escaped solvent vapors away before they can concentrate. Fans, outlets, and all electrical components are explosion-proof. Gas sensors mounted low to the ground (butane sinks) continuously monitor the air and trigger automatic fan purges if solvent levels reach even 10% to 25% of the concentration needed to ignite. The entire electrical system uses metal conduit, and a control box ensures the ventilation is always running when the room is in use.
Purging Residual Solvent
After extraction, the crude oil still contains dissolved butane that needs to be removed. This happens in a vacuum oven, where reduced atmospheric pressure lowers butane’s boiling point so it can be driven off at gentle temperatures that won’t damage the extract’s terpenes or cannabinoids.
Most extractors purge at temperatures between 85°F and 120°F under deep vacuum, typically around negative 29.5 inches of mercury. The process isn’t quick. A thorough purge generally takes 72 to 96 hours, with the slab of extract flipped periodically so trapped gas pockets can escape from both sides. During the early stages, the oil “muffins,” puffing up as large bubbles of butane escape. Temperatures are kept low initially (around 78°F to 95°F) to control this reaction, then gradually raised by a degree or two every several hours until bubble activity stops.
Rushing this step is how residual solvent ends up in finished products. In Washington State, for example, legal concentrates must test below 5,000 parts per million of residual butane to pass quality control. While that threshold sounds generous, well-purged extracts from experienced producers typically come in far below it.
Winterization and Refining
Crude BHO contains more than just cannabinoids and terpenes. Plant waxes, lipids, and fats also dissolve in butane and end up in the extract. Removing them through a process called winterization produces a cleaner, more potent product.
The process works by dissolving the crude extract in warm ethanol (about 130°F to 140°F) at a ratio of roughly 10 milliliters of ethanol per gram of extract. Once fully dissolved, the solution is placed in a freezer for at least 24 hours. As it chills, the waxes and fats become insoluble in the cold ethanol and precipitate out as solid particles. The mixture is then poured through a vacuum filtration system with progressively finer filter papers to catch those solids. Finally, the ethanol itself is evaporated off, either at its normal boiling point of 175°F or at much lower temperatures under vacuum, leaving behind a purified extract.
Why BHO Over Other Methods
The main advantage of butane extraction is terpene preservation. Compared to supercritical CO2 extraction, which uses high pressures that can degrade delicate terpene molecules, butane operates under milder conditions that keep more of the original flavor and aroma profile intact. This makes it easier to produce “full-spectrum” concentrates that reflect the character of the source plant, rather than a generic, stripped-down extract.
CO2 extraction has the advantage of being inherently safer since carbon dioxide isn’t flammable, and it avoids the residual solvent concerns that come with hydrocarbon methods. But it’s slower, requires more expensive equipment, and often sacrifices some of the aromatic complexity that consumers and patients value. Butane and CO2 extraction produce cannabinoid recoveries in roughly the same range, so the choice often comes down to whether a producer prioritizes terpene quality or the reduced regulatory burden of a non-flammable solvent.
Common BHO Product Types
- Shatter: A translucent, glass-like sheet that snaps when bent. Achieved by purging at lower temperatures with minimal agitation.
- Wax and budder: Opaque, softer textures created by whipping or agitating the extract during or after purging, which introduces air and disrupts the molecular structure.
- Live resin: Made from cannabis that was flash-frozen immediately after harvest rather than dried and cured. Freezing preserves volatile terpenes that would otherwise evaporate during drying, resulting in an extract with a stronger, more complex aroma.
- Sauce: A two-phase concentrate where THC crystallizes into solid chunks surrounded by a terpene-rich liquid layer. Produced by allowing the extract to slowly separate under controlled conditions.
The starting material, purging temperature, agitation, and post-processing steps all determine which of these textures the final product takes. The underlying extraction chemistry is the same across all of them.