CBD hash and residual solvents: what the COA must show
Hash made by dry sieving or ice-water washing involves no solvent, so there is nothing to purge and nothing to test for. A concentrate extracted with butane, propane or ethanol can keep traces of one, and its certificate of analysis should carry a "residual solvents" section with a figure for each solvent. No French text sets a limit specific to hemp, so the reference point is borrowed from pharmaceuticals.
Key takeaways
- Sieves, ice water, heat and pressure use no solvent, so they cannot leave a trace of one.
- Butane, propane and ethanol call for a purge, then a measurement to confirm it.
- That measurement relies on gas chromatography with headspace injection.
- The ICH Q3C guideline sets 2 ppm for benzene and 5,000 ppm for ethanol; butane and propane are absent from it.
- "Not detected" only means something when its limit of quantification is printed beside it.
Two families of processes, only one uses a solvent
The word "hash" covers products made in very different ways. The solvent question is therefore settled before any analysis, by reading how the batch was made.
| Process | What separates the resin | Solvent | Solvent section on the COA |
|---|---|---|---|
| Dry sift, static | Stacked sieves, electrostatic charge | None | Not applicable |
| Ice-o-lator, bubble, frozen | Ice water and filter bags | None | Not applicable |
| Rosin | Heat and pressure | None | Not applicable |
| Wax, crumble, shatter | Dissolution, then vacuum purge | Butane, propane | Expected |
| Ethanol extract | Dissolution, then evaporation | Ethanol | Expected |
The first three rows describe a physical separation, in which the trichome heads come away from the plant material without anything being dissolved; rosin simply adds heat and pressure. The last two rows describe a dissolution: the solvent carries away cannabinoids and terpenes and is then evaporated. A residue is left when that evaporation stops short.
Butane also makes production dangerous. According to a study published in 2015 in the Journal of Medical Toxicology, a Colorado burn centre admitted 29 patients burned during butane extractions between January 2008 and August 2014. Our guides to CBD wax and crumble describe this family and how it is purged.
What a residual solvent test measures
A residual solvent is the part of the extraction solvent still present in the finished product after the purge. It is invisible and your nose cannot reliably pick it up, so it has to be measured.
The standard method is gas chromatography with headspace injection. The sample is sealed in a vial and heated, the volatile compounds pass into the gas above it, and that gas is injected. The column separates the compounds, and a detector quantifies them. A review published in 2019 in the Journal of the American Society for Mass Spectrometry notes that many US states require this test, usually with a flame ionisation detector. Among the extraction solvents to look for, it lists hexane, ethanol, butane and propane. Mass spectrometry costs more but also identifies each compound, which helps when two peaks overlap.
The limit of quantification matters as much as the result. "Not detected" only means "below the threshold this method can measure". If the threshold is missing, the statement tells you nothing.
Reference limits: ICH Q3C, and nothing specific to hemp
No French or EU text sets a residual solvent limit for hemp extracts. Regulation (EU) 2023/915 on contaminants does set THC levels for food, 3.0 mg/kg for hemp seeds and 7.5 mg/kg for hemp seed oil, as the Belgian Federal Public Service for Health sums up. Extraction solvents fall outside its scope, and a resin is not a food in any case.
The available benchmark comes from medicines. The ICH Q3C guideline sorts solvents into three classes. Class 1 solvents are to be avoided, as known or strongly suspected human carcinogens and environmental hazards. Class 2 solvents are to be limited. Class 3 solvents have a low toxic potential, with an accepted exposure of 50 mg per day or more, equal to 5,000 ppm. The European Medicines Agency states that revision R9 has applied in the EU since 29 April 2024.
| Solvent | ICH class | ICH Q3C limit | California action level |
|---|---|---|---|
| Benzene | 1 | 2 ppm | 1 µg/g |
| Hexane | 2 | 290 ppm | 290 µg/g |
| Methanol | 2 | 3,000 ppm | 3,000 µg/g |
| Ethanol, acetone, heptane, pentane, 2-propanol | 3 | 5,000 ppm | 5,000 µg/g |
| Butane, propane | Not in the tables | None | 5,000 µg/g |
The last row matters most. Butane and propane, both common solvents for concentrates, appear in no ICH table. California's cannabis rules, which publish their own action levels, set them at 5,000 µg/g, or 5,000 ppm. That figure has no legal force in France. It does show the expected order of magnitude when a foreign certificate prints a column of limits.
Reading the section on a certificate: four checks
For a solvent-based concentrate, checking the section takes a few seconds.
- Match the batch. The number on the certificate has to be the one on the packaging, or the document is tied to nothing.
- Look for a list of solvents. A useful certificate names each solvent it tested, and a "compliant" or "PASS" mark with no list leaves you nothing to check.
- Find the limit of quantification, which comes with each result in ppm or µg/g.
- Check the laboratory's scope. The ISO/IEC 17025 standard sets competence requirements for testing laboratories, and Cofrac grants accreditation in France. Each accreditation covers specific tests, and one that includes cannabinoids may leave solvents out. Our method to check a laboratory's scope explains how.
There remains the case of a missing section. On rosin or washed hash, its absence is normal, since no solvent was used. On a wax or a crumble, it means data are missing. The comparison of concentrate certificates lists what each family should provide.
The catalogue's resins: what the product pages say
When checked on 23 September 2026, the CBD resins and hash category listed 15 products. Their pages describe separation in ice water or by sieving, followed by pressing, and state "no solvent". None of them mentions extraction with butane, propane or ethanol, so the solvent section does not apply.
These pages show a reference cannabinoid profile; as of 18 October 2026, no laboratory certificate had been published for them. The profile for Rosift CBG/CBD, batch PG-26-3A2B, shows 20.2% CBG, 4.6% CBD, 0.5% CBC and 0.4% CBN. Our laboratory page explains how to read the rest of an analysis file, pesticides and heavy metals included.
The process leaves the legal framework as it is. The decree of 30 December 2021 caps at 0.30% the Δ⁹-THC content of authorised varieties, hemp extracts and the products containing them, as our article on the legal THC level details. MILDECA, the French interministerial drug agency, notes that a CBD product may not make any therapeutic claim, under penalty of criminal sanctions. These products are sold to adults only and are not meant to be eaten.
Frequently asked questions
Not if it was separated mechanically. Dry sieving, ice-water washing and the rosin press use no solvent, so no butane can be left behind. A butane concentrate is purged under vacuum, and only the residual solvent test on its batch shows whether the purge went far enough.
Start with the process stated on the product page: ice water, sieves, heat and pressure. If the product is presented as extracted with butane, propane or ethanol, go on to the certificate. Its section should name each solvent and give both its limit of quantification and the measured result.
None specific to hemp extracts. The reference cited most often is the ICH Q3C guideline: 2 ppm for benzene, 290 ppm for hexane and 5,000 ppm for class 3 solvents such as ethanol. Butane and propane are not in it, and California caps them at 5,000 µg/g.
Only when the limit of quantification appears next to it. "Not detected" means "below the method's threshold", and a threshold of 10 ppm tells a different story from one of 500 ppm.
Written by the Phytogrammes team
Each journal article draws on cited primary sources: ANSM, EFSA, EUR-Lex and peer-reviewed publications. Product profiles are distinguished from documented laboratory results. Our approach.
Article published on . CBD is not a medicine.