Essential Oil Distillation
History - Distilling has been around for thousands of years, particularly in the production of alcoholic beverages. However, the process used for distilling essential oils includes water vapor and is therefore called Steam Distillation. The development of this process has been attributed to an 11th century Persian doctor named Avicenna who pioneered and documented many medicinal concepts still in use today including aromatherapy. Over the centuries the process and equipment have been refined and modernized, but the basic concept is still the same.
Process - There are three variations on the steam distillation process: 1) Hydrodistillation; 2) Wet Steam; and 3) Dry Steam. All of these function in the same basic way. The heat of the steam breaks down the plant fibers enough to expose the essential oil molecules, which are then carried by the water vapor up and out of the container. The steam/oil mixture is then cooled, condensing the water vapor back into a liquid, which drips into another container. Since the oil and water are different densities they will separate, with the oil usually being lighter than the water and rising to the top. Once separated, the oil can be extracted from the remaining water, which is called hydrosol.
Hydrodistallation is the simplest of the processes and is accomplished when the plant material is placed in the water, which is then boiled. While this method is required for some particularly woody plants, distilling oils from a plant such as lavender works best using the steam methods mentioned below.
Wet Steam distillation is a process where the plant material is suspended above the boiling water in the container by means of a screen or grid. This has the advantage of having the steam pass over more of the plant material, typically providing a higher yield of oil from a given amount of plant material than the hydrodistillation method.
The Dry Steam method has the boiling water in a separate container, and the steam is introduced below the plant material. The advantage of this method is that the plant material can be more easily changed without having to deal with the water in the same container.
Equipment - The three main components of distillation equipment consist of the retort, or still, the condensor, and the separator, with pipes to connect them. As you can imagine, the size, complexity, materials, and design of a still will vary greatly. There are small, primarily ornamental systems, table-top units for the hobbyist, medium sized systems for the small scale producer, all the way up large mass production systems. Some have mounted stills on large trailers that can be pulled into the fields (such as lavender) to avoid excessive handling of the plant material.
The original retort was probably a clay or copper pot. Modern units may be made from glass if part of a small system, and most of the larger containers are constructed of stainless steel. They may be fitted with a lid that is clamped down to withstand the steam pressure. On the larger systems the lid will be hinged in order to more easily recharge with plant material. Small units may be placed on a stove-top to heat, but most will have their own source of heat - typically a gas or propane burner. The medium or large retort will usually be insulated to conserve the heat and energy.
The condensor may be as simple as a length of pipe or coiled tubing, anything to provide surface area for the heat to escape the steam and allow it to condense back into liquid. Some means of cooling the condensor may be employed to aid in this process. The condensor pipe could pass through water or ice, or the condensor could be an actual component that contains a heat exchanger through which cooling water passes, absorbing the heat from the steam. This is similar to the method used by a refrigerator to remove heat from the inside.
The separator is simply a container that has a pipe attached near the top (or bottom). As the liquid rises in the container and the oil floats to the top (or sinks to the bottom), the pure oil can be drained off leaving the diluted oil/water mixture called hydrosol behind.
In the case of lavender, the oil is removed from the top and the hydrosol is used for non-therapeutic purposes. It will still contain a pleasant aroma and can be used to provide scent, such as adding some to the laundry to take advantage of that wonderful smell.
Video - Watch the two part video at the links below to see a still and hear the distillation process described.
Lavender Distillation Video Part 1
Video Part 2
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