Residual Solvents
Also known as: Residual solvent testing, Solvent residue
Residual solvents are traces of the liquids or gases used to pull cannabinoids out of hemp, such as ethanol, butane, propane, and hexane, that remain in the finished extract and are measured on a certificate of analysis (COA) in micrograms per gram.
Extraction needs a solvent. Ethanol is used to extract and to winterize. Butane and propane are used in hydrocarbon extraction. Hexane turns up in some industrial processes. None of these are meant to end up in your bottle, but a poorly purged batch can carry some through. Labs test for them with headspace gas chromatography, and the panel can screen dozens of compounds in one run. One national hemp panel we looked at (ACS Laboratory, checked October 2026) lists 55 analytes.
Limits depend on who is setting them, and there is no single federal number for hemp products. As one example, California's rule for cannabis products (Cal. Code Regs. Tit. 4, § 15718, checked October 2026) sets action levels of 5,000 µg/g for butane, propane, and ethanol, 290 µg/g for hexane, and 1.0 µg/g for a short list of Category I solvents such as benzene and chloroform. That is a state cannabis rule, not a hemp CBD standard, so use it as a yardstick for what a serious lab report looks like, not as our legal limit.
CO2 extraction changes the picture. Pressurized carbon dioxide is not a liquid solvent that has to be evaporated off, so a CO2-only batch has far less to purge. It does not make the panel pointless: many CO2 extracts are later winterized in ethanol, and some are refined further. That is why the panel exists, and why we say read the report rather than the label. Look for the residual solvents section, check the result against the limit it lists, and be wary of a COA that skips the section entirely.
Related terms
- CO2 ExtractionCO2 extraction uses pressurized carbon dioxide, held in a supercritical state between liquid and gas, to pull cannabinoids and terpenes out of hemp without a chemical solvent.
- WinterizationWinterization is a purification step that removes plant fats, waxes, and lipids from a crude hemp extract by dissolving it in ethanol and chilling it until the waxes drop out.
- COA (Certificate of Analysis)A COA is a document from an accredited third-party lab certifying what is — and isn't — in a CBD product.
- Third-Party TestingThird-party testing means a CBD product was analyzed by an independent, accredited lab — not by the manufacturer themselves.
- ISO 17025ISO 17025 is the international quality standard for testing and calibration laboratories. CBD COAs should come from labs accredited under this standard.