There are different ways to extract essential oils, including distillation, expression, enfleurage, carbon dioxide and the use of solvents. The most common extraction methods are steam distillation and cold expression. 

Steam Distillation

The most used extraction techniques are steam distillation and hydrodistillation. In steam distillation, water is heated, and high-pressured steam passes through the plant material. This allows the essential oil to evaporate, which is collected through a coil. Cold water is then used to cool it off and condense the steam. This process separates the water and the essential oil. The essential oil floats on top of the water; a byproduct which is referred to as hydrosol. This process should be carried out quickly so that the hot steam doesn’t affect the heat-sensitive essential oils. Some essential oils must be redistilled to remove impurities and oils like Ylang Ylang need to be distilled multiple times in order to capture different grades of their essence. For hydrodistillation, the plant material is completely covered with water and made to boil. This can be done at lower temperatures and pressures. Water is added to protect the essential oil from overheating and hydrodistillation is often applied to delicate plants like Neroli and Rose. As hydrodistillation is a slow process, it is used for oils that are not damaged due to extended contact with hot water. The shelf-life of distilled essential oils is 2 to 5 years. 

Cold Expression

Cold expression is the technique employed to extract essential oils from citrus fruits, which are contained in the spores of the rind. The fruit's rinds are dumped into a rotating drum with rows of spikes that strip the fruit of its peel. The mixture of essential oil and any other cell content is then washed by water and run through a centrifugal separator; a process that is carried out very rapidly. The shelf-life of expressed oils is 6 to 9 months.