Cannabis extraction takes the resin out of the plant and leaves the rest behind. The resin holds the cannabinoids, such as THC and CBD, and the terpenes, the compounds that give each strain its smell. Every extraction method belongs to one of two families. Solvent methods dissolve the resin in a liquid or a pressurised gas, then remove that solvent. Solventless methods separate the resin physically, with cold water, screens, or heat and pressure.
The family you choose decides three things: what ends up in the concentrate, what you must clean out afterwards, and which hazards you must control. This article compares the main methods, explains the fire and residue risks, shows how to calculate yield, and sets out what Thai law allows.
What extraction is separating
Cannabinoids are not spread evenly through the plant. AGES, Austria’s federal food safety agency, describes them as stored mainly in special glandular hairs in the flowering part of the plant. Smaller amounts sit in the leaves and stems. These glandular hairs are called trichomes: the tiny resin heads you see as frost on a ripe bud.
Extraction is therefore a concentration step. The goal is to move as much resin as possible into a small mass. What you leave behind is plant fibre and, depending on the product, chlorophyll (the green pigment), plant waxes and water-soluble material.
No method does this perfectly. A review of medicinal cannabis processing in the Journal of Cannabis Research compared the methods like this:
- Dry sieving and ice water extraction collect whole trichome heads.
- Hydrocarbon methods (butane, propane) leave water and pigments such as chlorophyll behind.
- Ethanol also pulls out flavonoids, a group of plant pigments.
- CO2 can be tuned to extract different compounds, depending on pressure and temperature.
The same review lists the solvents in use: ethanol, butane, propane, hexane, CO2 and even olive oil.
What you can do: before choosing a method, write down the end product you want. Full-spectrum oil, a high-THC concentrate for testing, and hash for a traditional recipe each point to a different method.
Solvent methods
A solvent dissolves the compounds you want. Solvents are often described as polar or non-polar. Polar solvents, like water and ethanol, also dissolve water-loving material such as chlorophyll. Non-polar solvents, like butane and CO2, dissolve oily material such as resin and leave most water-loving material behind.
CO2
Carbon dioxide becomes a supercritical fluid above roughly 31 °C and 74 bar. In that state it is neither a normal gas nor a normal liquid. It flows into plant material like a gas but dissolves resin like a liquid. It behaves as a non-polar solvent. Changing the pressure and temperature changes which compounds dissolve, so one machine can target different fractions.
The review notes that CO2 does not burn and is easy to remove. When the pressure drops, it turns back into gas and leaves the extract. That is why CO2 extracts do not raise the residual solvent question the way liquid solvents do. The cost is the equipment: everything runs inside high-pressure vessels rated for that pressure.
Ethanol
Ethanol (drinking alcohol, in pure form) is polar enough to dissolve cannabinoids. Because it is polar, it also pulls out chlorophyll and waxes, especially at room temperature. That gives a dark, grassy extract. Chilling the ethanol before use reduces this.
After extraction the ethanol must be evaporated and recovered. Ethanol vapour burns easily. So ventilation and control of sparks and flames are part of the method itself, not an optional extra.
Hydrocarbons: butane and propane
Butane and propane are gases at normal room conditions. Under pressure or cold they become liquids. The liquid is passed through plant material, dissolves the resin, and is then evaporated off.
Butane boils at about −1 °C. That makes it easy to drive off the extract. The same property makes it dangerous: at any normal room temperature it turns to vapour. A review of butane hash oil production described the risk directly. Amateur extraction, often called “blasting”, can leave flammable vapour collecting in closed rooms. A spark or a static shock then ignites it.
What you can do: if you only want to understand or buy solvent extracts, check which solvent was used and ask for a residual solvent test. Do not attempt solvent extraction yourself. The safety section below explains why.
Solventless methods
Solventless concentrates are made without adding any solvent.
- Dry sift: dried flower is shaken over fine screens. The trichome heads fall through and the plant matter stays on top. The result is often called kief. The Journal of Cannabis Research review cites dry-sieved kief at roughly 35–50% THC. See Dry Ice, Dry Sift and Charas.
- Ice water separation: plant material is stirred in ice-cold water. The cold makes trichome heads brittle, and the stirring breaks them off. The heads are then collected in mesh bags and dried. See ice water extraction and bubble hash.
- Rosin: heat and pressure squeeze the resin out of flower or hash, usually between two heated plates. See rosin.
Ice water hash and rosin have their own detailed topics, so they are only summarised here. The review also notes two limits. These long-established methods are thinly covered in scientific studies, and they are hard to scale up to large volumes.
Translator’s note: ice water hash comes out wet and must dry fully before storage. In the Thai rainy season, room air often stays very humid, so wet hash dries slowly and can grow mould. Dry it in an air-conditioned room or with a dehumidifier, and do not start a wash if a power cut could stop your drying equipment overnight.
What you can do: if you are new to concentrates, start with dry sift on a small amount of trimmings. It needs only screens, carries low risk, and shows you how much resin your material actually holds.
How the methods compare
| Method | Family | What it tends to carry over | Main hazard to control | Typical clean-up |
|---|---|---|---|---|
| CO2 | Solvent | Adjustable with pressure and temperature | High-pressure equipment | Often winterized in ethanol afterwards |
| Ethanol | Solvent | Broad; chlorophyll and waxes unless chilled | Flammable vapour | Evaporation, residual solvent testing |
| Butane / propane | Solvent | Non-polar resin, little water or chlorophyll | Explosive vapour | Purging, residual solvent testing |
| Ice water | Solventless | Whole trichome heads | Low; wet material must be handled cleanly | Drying |
| Dry sift | Solventless | Trichome heads plus some fine plant matter | Low | Repeat sieving |
| Rosin | Solventless | Resin melted from flower or hash | Hot plates | Filtering |
Three clean-up terms in the table need a short explanation:
- Winterization: the extract is dissolved in ethanol and kept very cold. Waxes and fats harden and separate, and are then filtered out.
- Purging: the extract is gently warmed, often under vacuum, so leftover butane or propane evaporates out of it.
- Residual solvent testing: a laboratory measures how much solvent is still in the finished product.
The table does not rank the methods. A medical manufacturer, a lab running potency tests and a hash maker each need a different end product, so each will choose differently.
Turning crude extract into distillate
Many solvent extracts are a first-stage “crude” oil. Some producers refine it further into distillate, a clear oil that is mostly one cannabinoid with most terpenes and other compounds removed. Distillation heats the oil under strong vacuum, so cannabinoids evaporate at a lower temperature than normal, and then condenses them again.
Two kinds of equipment are common:
- Short-path distillation: the vapour travels a very short distance from the heated flask to a cooled condenser. It suits small batches, but the oil stays hot for longer.
- Wiped-film distillation: a rotating wiper spreads the oil as a thin film on a heated wall, so each part is heated only briefly. It suits continuous, larger-scale work.
Both run at high temperature under vacuum, and the result is usually a concentrate well above the 0.2% THC line discussed in the Thai section below. In Thailand this is licensed industrial work, not something to try at a farm.
Calculating extraction yield
Yield tells you how much concentrate you got from your starting material. It lets you compare methods, batches and input material on the same basis.
The basic formula:
Yield (%) = weight of finished extract ÷ weight of starting material × 100
A worked example with round numbers, for illustration only: you sieve 200 g of dried trim and collect 10 g of kief. Your yield is 10 ÷ 200 × 100 = 5%.
Weight yield alone can mislead. A dark, waxy ethanol extract can weigh more than a clean one while holding the same amount of THC. So also calculate how much of the cannabinoid you actually recovered, using lab results for both the input and the extract:
Cannabinoid recovery (%) = (extract weight × extract THC %) ÷ (input weight × input THC %) × 100
Continuing the example: the trim tests at 10% THC, so 200 g holds 20 g of THC. The kief tests at 40% THC, so 10 g holds 4 g of THC. Recovery is 4 ÷ 20 × 100 = 20%.
What you can do: weigh the input and output of every batch and record them with the date, material and method. After a few batches you will know which material is worth processing and which method suits it.
Safety: fire and residual solvent
Two hazards dominate solvent work.
Fire and explosion
Butane vapour collects in low spots and ignites, as described above. Ethanol is less dramatic but still a real fire risk. OSHA, the US workplace safety agency, lists two figures for ethanol:
- Flash point: 55 °F (about 13 °C). This is the lowest temperature at which a liquid gives off enough vapour to catch fire from a spark or flame.
- Lower explosive limit (LEL): 3.3% in air. This is the lowest concentration of vapour in air that can ignite. Below it the mix is too thin to burn; at or above it, one spark is enough.
Neither solvent belongs near an open flame, a hot plate, or electrical fittings not rated for flammable areas. That is why commercial solvent extraction takes place in rated rooms with gas detectors and extraction fans. It is also why this article does not describe home procedures.
Commercial hydrocarbon extraction uses closed-loop systems. In a closed loop the solvent stays inside sealed, pressure-rated vessels. It is pumped through the plant material, separated from the extract, and recovered for reuse, instead of being released into the room. Open “blasting” does the opposite: it releases the vapour into the air around the operator, which is how the fires described in the butane review start.
Translator’s note: in Thailand, room and shed temperatures usually sit around 30–35 °C. That is far above ethanol’s 13 °C flash point, so open ethanol gives off flammable vapour all year round, not just on hot days. Butane, which boils at about −1 °C, is always a vapour at Thai temperatures. A power cut also stops extraction fans and gas detectors at exactly the moment vapour may be building up. Any licensed facility should have backup power for ventilation and detection, and should store solvent away from the work area.
What stays in the product
The second hazard is solvent left in the finished extract. The reference used in the pharmaceutical industry is the ICH Q3C guideline on residual solvents. It measures solvent residue in ppm (parts per million). 10,000 ppm equals 1%.
- Ethanol is in Class 3, solvents with low toxic potential. Up to 5000 ppm (0.5%) is accepted without further justification.
- Hexane is in Class 2, with a much tighter limit of 290 ppm.
Cannabis-specific rules differ from country to country. The principle is the same everywhere: you cannot treat a solvent extract as safe until a lab test shows the solvent has been removed to an accepted level.
Translator’s note: at least one Thai laboratory, at NSTDA, lists residual solvent testing among its cannabis and hemp services. Before you buy or make any solvent extract, ask the testing lab whether it runs this test and against which limits. If no lab can test it, treat the product as unverified. See How to Read a Cannabis Certificate of Analysis for what a lab report should show.
Common mistakes
- Treating “solventless” as “tested”. No added solvent does not mean the potency is verified or that the product is free of contaminants such as mould or pesticide residue. A solventless concentrate still needs a lab result.
- Assuming CO2 extract needs no further processing. CO2 crude is often redissolved in ethanol and winterized to remove waxes. One published hemp protocol held the ethanol solution at −20 °C for 24 to 48 hours before filtering.
- Comparing extract and flower percentages directly. Kief at 35–50% THC, and solvent concentrates at higher figures, belong to a different category from flower. Dose, label and store them as concentrates, not as strong flower. See Reading a Concentrate Label.
- Reading a low boiling point as a safety margin. A low boiling point makes a solvent easy to remove. It also makes it easy to ignite.
Translator’s note: the −20 °C step needs a freezer that holds that temperature for one to two days. In areas with frequent power cuts, a cut during winterization lets waxes melt back into the solution, and the step must be repeated.
Thai law on extracts
In Thailand the cannabis plant was removed from the narcotics list in 2022. Extracts containing more than 0.2% THC by weight, however, remain Category 5 narcotics. See Controlled Herb vs Category 5 Narcotic for how the 0.2% line works.
The Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569 took effect on 26 April 2026. Licences for extracts above 0.2% THC are granted only to three kinds of holder:
- Thai juristic persons that are not “foreign” under the Foreign Business Act B.E. 2542 (1999);
- state agencies;
- the Thai Red Cross Society.
The regulation also limits production, import, export, sale or possession of such extracts to specific purposes, such as official narcotics control, medical use, medical or scientific research, and industrial use.
Separately, cannabis flower itself is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568, in force since 26 June 2025. Unlicensed processing of a controlled herb is an offence under Section 46 of the Thai Traditional Medicine Protection Act B.E. 2542 (1999). Section 78 sets the penalty at up to 1 year in prison, a fine of up to 20,000 baht, or both. For the full picture of what changed in April 2026, see Thailand’s Two Ministerial Regulations of B.E. 2569.
What you can do: if you are considering extraction work in Thailand, first read the current text of the B.E. 2569 extracts regulation. Then confirm with the licensing authority which licence covers your planned product, before you buy equipment or process any material.
Discussion
Have a question about a method, a lab result or yield figures from your own batches? Post it below this topic. Please keep to the forum rules: no sales offers and no step-by-step instructions for home solvent extraction.
References
- AGES (Austrian Agency for Health and Food Safety): information on cannabinoids and where they are stored in the cannabis plant.
- Lazarjani et al. (2021), “Processing and extraction methods of medicinal cannabis: a narrative review”, Journal of Cannabis Research 3:32.
- Review of butane hash oil production and its hazards.
- OSHA (US Occupational Safety and Health Administration): ethanol flash point and lower explosive limit.
- ICH Q3C guideline: Impurities — Residual Solvents.
- Published hemp extraction protocol describing winterization at −20 °C for 24–48 hours.
- Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569 (Thailand).
- Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568 (Thailand).