Solvent Extraction

While water is technically a solvent, other solvents are often used for herbal and botanical extraction. Commonly used solvents can include methanol, ethanol, hexane, and petroleum ether. A solvent is selected for suitability with the desired solute, and is added to plant material that has been finely milled to optimize penetration and extraction.

Solvent processing requires scientific expertise and technical process control, from the material fineness to solvent selection to time and temperature controls. It’s a useful method for more delicate plant materials whose essences aren’t readily extracted by steam.

Some solvents can leave a residue, and residue levels are strictly regulated. Lab analysis capabilities such as gas chromatography-mass spectrometry are crucial for determining the composition and quality of the final product.

The solvent, selected for its affinity with the desired plant compounds, flows through the prepared biomass to penetrate the plant structures and release the essential oils. The resulting mixture of solvent, plant oils, and botanical solids is typically filtered and vacuum distilled to remove as much solvent as possible, especially when petroleum-based hydrocarbons are used. A small percentage of chemical solvent residue can remain in the final product.

Vanilla extract is an example of a commonly used solvent extraction. The essential oils from the plant remain in alcohol, which was used to extract the desirable aromatic compounds from the structures of the vanilla bean pods.