Stage 4. Primary extraction of the dried and milled Cannabis plant material.
The dried and milled plant material will be extracted with the solvent of choice (e.g. ethanol) to generate a liquid extract of the Cannabis plant. This crude extract will contain the cannabinoids, the terpenes and the waxes (along with chlorophyll and other
chemicals). Alternative solvents include other gaseous solvents (e.g. propane, butane, CO2, etc.) or liquid solvents (e.g. Ethanol, Methanol, Hexane, etc.). Solvent-extracted material needs to be concentrated by the evaporation of the solvent from the extract. With gaseous solvents, this occurs automatically as the product is returned to atmospheric pressure. With liquid solvent extracts, the solvent needs to be carefully evaporated in order to concentrate the extract. Careful processing conditions (e.g. minimal heating) needs to be employed if the cannabinoids are to be retained in their acid forms. The choice of the primary extraction solvent requires consideration of the extraction efficacy (getting a large proportion of the cannabinoids out of the plant material), selectivity of extraction (getting the cannabinoids out of the plant material without unwanted components like chlorophyll), etc. Many extraction solvents produce an extract that contains a significant amount of chlorophyll that will need to be removed as the product is further purified.
Extract the dried medicinal cannabis material (ratio of solvent volume to plant mass should be 20:1v/w or more) to yield 10-15% of the original weight as an extracted concentrate. Cannabis concentrates are viscous and sticky substances that can be produced by extraction with a variety of solvents (e.g. propane, butane, hexane, petroleum ether, naphtha), alcohols (e.g. ethanol, isopropanol) and subcritical or supercritical CO2.
Â Stage 5. Removal of chlorophyll from the Cannabis extract.
The presence of chlorophyll complicates the isolation and purification of other more
important groups of phytochemicals from the Cannabis extract. The concentrated extract can be mixed with a solvent (e.g. ethanol) and applied to a resin (e.g. charcoal, alumina, silica) that binds some of the chlorophyll from the crude extract while leaving most of the cannabinoids, terpenes, waxes and other chemicals unbound.
Stage 6. Removal of plant waxes from the Cannabis extract (Winterisation).
The decolourised extract in ethanol will be cooled to –20oC for 2-3 days in a sealed container. The waxes will solidify and can be removed with filtration of the cold ethanol solution.Â Winterization can remove unwanted plant waxes.Â This step involvesÂ dissolving the concentrated extract in 5-10 volumes of ethanol, freezing this solution at >-20oC for 24-48 hours, filtering out the unwanted precipitate (solidified waxes), and removing the ethanol from the filtrate by evaporation.