There are several ways to extract essential oils out of plants. When exploring essential oils, it is a good idea to know how they are produced, and what the advantages and disadvantages of each method are.

1. Steam Distillation
   Steam distillation is the most common and in many cases the most effective method of obtaining an essential oil. Steam is passed through ground plant parts in a still vessel, which releases the oils and turns them into vapor. The vapor is then passed through a condenser and cooled back into liquid. The oil from the liquid separates from water and is then collected in a receptacle called a separator.
   

2. Solvent Extraction
   Solvent extraction is used for thick resins and plants too delicate for the distillation process. Plant material is mixed with a solvent such as ethanol to isolate the essential oils. The resulting waxy mixture is known as concrete. Concrete is then mixed with alcohol to produce aromatic vapors, which are then condensed and collected. The resulting concentrated liquid is known as an Absolute.
   
   Solvent extraction is considered the least ideal of the methods, since residual portions of the solvent and other plant compounds can appear in the final product.
   
   When choosing between two aromatherapy brands, stick with the oil that is obtained through steam distillation or is not absolute. Some oils, like vanilla, are mainly absolutes.
   

3. CO2 Extraction
   CO2 extraction is similar to steam distillation, except carbon dioxide is used instead of steam. When CO2 is pressurized, it becomes liquid while still remaining a gas. This is known as a “supercritical” state. The use of forced supercritical CO2 eliminates any risk of heat damage because of the lowered temperatures.
   

4. Maceration
   Plant material is ground into a powder and placed in a vessel. A solvent is added and the mixture sits for one week. The liquid is then strained and the plant matter is pressed to extract the remaining liquid. Afterwards, the liquid is clarified and the essential oil is obtained.
   
   One advantage of maceration is that more of the plant’s essence is retained, due to the larger remaining molecules from the physical nature of the process.
   

5. Cold-Press Expression
   This method is mainly used for citrus peels. First, the fruit is pierced so that the essential oils sack can leak their liquids. Then the fruit is pressed to obtain the remaining liquids. A centrifuge then separates the essential oils, juices, and remaining plant matter. Since the oil will rise higher in the centrifuge, it is easily siphoned off.
   

6. Water Distillation
   Water distillation is similar to steam distillation, but boiling water is used instead of forced steam. This protects delicate plants such as flowers and prevents clumping. The water vapor caused by boiling is condensed and separated into the essential oil. The remaining boiled water is known as floral water. Rosewater liquid is a type of floral water.
   

7. Enfleurage
   Enfleurage is an archaic method of obtaining essential oils and is rarely used today. Flowers are combined with animal fat and are pressed between two pieces of glass. Flowers are added or replaced until the fat contains the desired aroma. The fat is washed in alcohol which dissolves the essential oils. The alcoholic mixture is then heated, burning the alcohol off and leaving the oils behind. The left over fat is used to make soap.

For a more comprehensive guide to extraction methods, click here.