What is Distillation and How Does it Work?

What is Distillation and How Does it Work?

Distillation is the art of removing these precious chemicals via high pressure steam or mix of steam and boiling water. To begin distillation, the appropriate amount of plant material is packed into a hopper. The canister is sealed to create atmospheric pressure. The correct amount of water is added for that batch and then heated. Steam is created by either boiling the water in the hopper or injecting steam and forced through the pressurized hopper or vessel containing the plants. The heat of the steam ruptures the molecules in the plant and carries the particles of essential oil and other constituents through a cooling system into another container. When the steam passes through the cooling unit, it reverts back to water, where it separates from the essential oil  because of their different densities. Essential oils are lighter than water and will therefore float on top. Water soluble chemicals will stay mixed with water creating extracts or hydrosols. Following is a brief description of three basic methods.

Water Distillation
For this method, the plant material is submerged in water. The water is then heated to boiling point  During this process, there is direct contact between boiling water and plant material.  All parts of the plant material must be kept moving by the motion of boiling water. This method is used with plant material that can’t be easily be broken down with steam or water and steam distillation such as cinnamon bark.

Water and Steam Distillation
Water and steam distillation methods employ the same basic equipment as water distillers. The fundamental difference is the plant material is set on a perforated grill above the water as opposed to being immersed in the water. This method is more energy efficient as the essential oil is produced at a much faster rate with higher yields. Thermal degradation is reduced as well. Many oils which contain significant aldehydes such as lemongrass are still produced this way.

Direct Steam Distillation

This type of distiller is designed quite differently than water and water steam distillers. There is no water in the hopper with the plant material. Steam is generated in a separate boiler chamber and then injected into the plant material from outside the still. The plant material is placed on a perforated grid above the steam inlet. A real advantage of steam generation is that the amount of steam can be readily controlled. Because steam is generated in a satellite boiler, the plant material can be heated at lower temperatures of 90- 100° C reducing thermal degradation.  A drawback to steam distillation is the much higher capital expenditure on such equipment.  Many mass produced essential oils such as rosemary,  lavender and eucalyptus, are produced this way

Do All Plants Produce Essential Oils?

No they don’t.  In fact of the hundreds of thousands of plant species, only a few thousand may be capable of producing an essential oil.  Therefore, when companies state that essential oils are the “life blood of a plant” this is not true.

Can Any Plant be Distilled?

Theoretically, you can distill any plant material, however, you may not like the results. Distillation is reserved for plants which are capable of producing an essential oil and not easily damaged by heat.  Jasmine is one of the most coveted aromatic oils in the world but it can’t be distilled without serious thermal degradation which destroys the aromatic properties that make it so precious.

Given that it takes thousands of pounds of petals harvested during a few weeks of the year and a few hours of those days to produce even a few ounces of oil through other effective methods of extraction, it make no economical sense to waste any petals on distillation to produce an inferior product.

Are Plants Which Do Not Produce Essential Oil Distilled?

Some plants such as witch hazel or sweetgrass which don’t produce an essential oil are distilled because their water is coveted for aromatic, spiritual and medicinal properties.  Others can be concentrated to create water soluble  extracts such as cucumber or green tea.

Are all Plants Distilled in the Same Amount of Time?

The amount of time for distillation per batch of plant material has a vast range dependent on the quality of oil required and the plant material itself. This is where expertise of specific plants is necessary to produce a quality oil or one to specific industry standards. For example, lavender can be distilled in one to two hours depending on batch size, whereas clove or cinnamon take much longer.

Different distillation times of a particular plant will create different grades.  Ylang Ylang, a prized aromatic oil, has several grades (extra, 1 , 2, 3 and dark).  The grades are indicative of distillation time with “extra”  and 1 being the shortest time, which produces the lowest yield, best aromatic properties and highest price.  The perfume industry purchases most of these grades leaving very little for public consumption.  Grade 3 and dark, produce more oil because of longer distillation time, but is not considered fragrantly appealing so the price is dramatically reduced.  These grades are usually destined for industrial purpose.

There is also no such thing as 2nd or 3rd distillation.  A batch of plant material is distilled once and then discarded.  Most often the plant material is spread back in the fields to provide nutrients and act as ground cover to reduce weeds.

Can an Essential Oil or Liquid Plant Extract be Distilled?   

Yes it can.  This is most often done to further process an oil to remove impurities or reduce high amounts of hazardous chemicals.  Peppermint which may contain 50-80% menthol on initial distillation can be re distilled to reduce levels  under 40% content, making the oil more aromatic and safer to use.  The menthol crystals that are removed are usually sold to pharmaceutical companies.  Bitter orange which is initially expeller pressed, is then distilled to remove water and other impurities.  many citrus oils are extracted via cold pressing but then distilled to remove photo sensitizing chemicals or isolate other aroma chemicals.  This process is called “Folding”