Concrete, Resinoid, Absolute
Sometimes these three terms get a bit confusing, so we decided to try and make it simpler. We need to say a word here about solvent extraction in order to understand concrete and absolutes. Solvent extraction involves the use of oil soluble solvents, such as hexane, di-menthylenechloride, and acetone. During solvent extraction the substances extracted during the solvent extraction method are placed in a distillation vessel and gentle heat is applied. This heat is just enough to recover the solvent still in the mixture (the solvent is re-used), and no volatile constituents of the oil are driven off.
What is left after the solvent has been removed after solvent extraction is a near solid wax-like substance called a ‘concrete’. Should resinous botanical material have been used to extract, the result would be called a ‘resinoid‘ instead of a ‘concrete’. An example of resinous material would be frankincense and myrrh.
Absolutes are technically not “essential oils’ but are “essences.” An absolute is made by taking a concrete and melting it by warming with some alcohol and then stirring it. They are obtained from the grain alcohol extraction of a concrete, which is the solid waxy residue that is derived from the extraction of plant materials. The essential oil, some waxes, fixed oils and fats then dissolve in the alcohol. The alcohol mixture is then distilled in a vacuum to remove the alcohol, and the remaining substance is an ‘absolute’. An absolute is the most concentrated form of fragrance (and the most costly), and is mostly used in the perfume industry. Flower petals are usually used to get absolutes. This method of extraction is used primarily for botanical’s where the fragrance and therapeutic parts of the plant can only be unlocked using solvents. Jasmine and neroli are extracted this way.