At 91.4°F, carbon dioxide gas becomes almost liquid — supercritical. Technically, it is neither a gas nor liquid, but under pressure, it acts like a solvent and can be used to produce hypercritical extracts of plants. When the pressure is released, there are no residues so the plant material is pure, including being free of heavy metals. This method of extraction has been used in the food industry for some years and is gaining momentum in the essential oil world though technically speaking the extractions are more like concentrates than essential oils. They can be used as flavoring and in ointments and herbal formulas. All CO2 extracts are soluble in oil.