Most flowers contain too little volatile oil to extract with high heat or steam. Their chemical components are too delicate and easily denatured. Instead, a solvent such as hexane or supercritical carbon dioxide is used to extract the oils. Extracts from hexane and other hydrophobic solvents are called concretes, which are a mixture of essential oil, waxes, resins, and other lipophilic (oil-soluble) plant material.
The use of solvents gives a higher yield and also keeps the more water-soluble components intact, which would otherwise be lost in distillation. Extracts from hexane and other
hydrophobic solvent are called concretes, which are a mixture of essential oil, waxes, resins, and other lipophilic (oil soluble) plant material.
Below is an example of the basic equipment that is needed for the extraction of essential oils with a volatile solvent, coupled with a vacuum still for recovery of the solvent after extraction.
Although highly fragrant, concretes contain large quantities of non-fragrant waxes and resins. Often, another solvent, such as ethyl alcohol, which is more polar in nature, is used to extract the fragrant oil from the concrete. The alcohol is removed by evaporation, leaving behind the absolute. Absolutes are a slightly less expensive essential oil extraction method than enfleurage.