All of the Rose Rosa damascena I have used up until this point has been an absolute, as this has been the most affordable way for me to enjoy the aroma and benefits of Rose. Just when I thought I was blown away and satisfied enough with the absolute, I was notified about a bulk direct sale with a Turkish producer of Rose Otto Rosa damascena and had to bite when I saw the discount. It arrived yesterday and worth every cent…if only to smell the aromatic differences.
Although both are from the same family of Rose, the essential oil that has been hydro steam distilled is known as Rose Otto while the Rose extracted via the solvent method is known as Rose Absolute.
So what is the difference between these two methods?
Solvent extraction is usually used for plants whose essential oils would be compromised by steam distillation either because they can’t handle too much heat (flower petals where the essential oil is stored such as in Rose or Jasmine can be too delicate), the plant contains a lot of resin or the part of the plant has a low concentration of essential oil.
The basic idea of solvent extraction is this: the plant material is mixed with a solvent (usually acetone, benzene or hexane) which pulls out the essential oil. This is known as an extract and it is placed in a still with gentle heat that removes the solvent, but not the essential oil. When the extract is cooled it solidifies into a wax. The wax is removed with alcohol, into which the essential oil dissolves. The alcohol/oil mixture is chilled and the alcohol is removed via a vacuum extraction with the final residue left over being an absolute.
Solvent extracted oils have a wonderfully full aroma but the downside is that waxes and other non-volatile materials can be extracted along with the essential oils. The result is a much thicker oil that can actually solidify in room temperature. There is debate as to whether oils extracted in this way are true essential oils or not, therefore the term absolute is used.
In steam distillation the plant material is placed in a copper still with water. Heat is applied at the bottom and as the still is heated, the plant sacs containing essential oils open. The oils vaporize and are carried up via steam into a condenser where the steam and oil are separated, take on their respective forms (steam to water) and collect into the receiver. Since oil and water don’t mix, the essential oils form a layer on the top of the condensed water and are collected and filtered. Hydro steam distillation is a variation on this method in that the plant material is placed in water and heat is applied from the top instead of the base. Condensation of the oil/steam happens inside the still below the plant being processed. The benefit to this is less steam (therefore less heat), a shorter processing time and higher yield of pure, unadulterated essential oil.
Below are pictures of the hydro steam distillation process. Source: Appalachian Vally Natural Products (click to enlarge).