Residual Solvents: As cannabis extracts are becoming more common, these extracts are making their way into foods, candies, vapor pens, and who knows what else tomorrow. These extracts are typically made using a solvent and extreme cold temperatures. As the extract returns to ambient temperature the solvents should boil off; however, this is not always the case and there can be residual solvents found in the extract.
If the extraction process is done correctly you will end up with a 99.9% pure extract. The most common solvents are methane, ethane, propane, butane, and pentane. All of these solvents and others are harmful if consumed in any amount. Less than 500 ppm of residual solvent per one gram of extract has been deemed safe for human consumption by the state of Washington.