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Part 3: Distillation Methods—Distillation
There are many methods available for collecting essential oils, but some general principles apply to all methods. First, plant materials generally produce the best yield if distilled whole. To avoid loss of any essential oil, the plant material should not be cut, chopped, or altered in any other way before the distillation procedure begins. Some plants cannot be packed into the distillation machinery in their whole form. For example, sandalwood essential oil is derived from the dense heartwood of the sandalwood tree. This is one exception in which proper distillation of the oil would be impossible without first grinding the wood into small chips that more easily fit into the distillation still.
To protect the integrity of the essential oil’s delicate chemical profile, all distillation methods require careful attention to time, temperature, and pressure. Each of the aromatic compounds that make up an essential oil has a different sensitivity to heat. Some molecules will remain completely unaffected by high temperatures while others are very delicate and can be destroyed if the temperature of the system gets too high. Meticulous control of the distillation conditions is vital to successful essential oil production.
Distillation is a process that involves separating a substance into its constituent parts based on their boiling points or volatility. This means that when exposed to high temperatures, constituents in a liquid mixture will change to their gaseous phase. Each individual constituent boils at a different temperature, so depending on the temperature of the system, some constituents will be in their gaseous phase while others will remain as a liquid. If the temperature is carefully controlled, this process allows different constituents to be isolated from one another. It is important to know that distillation involves only a physical separation of compounds without any sort of chemical reaction, thus protecting the intricate chemical profile of the essential oil.
There are many types of distillation. We will begin by describing the most basic method, simple distillation, to help you develop a fundamental understanding of how the process works. Keep in mind that simple distillation is not an acceptable method for collecting high quality essential oils. A more complex and controlled method called steam distillation is required.
Simple distillation requires a special apparatus commonly called a distillation still. The still has three basic parts: a heating chamber, a condensing tube, and a collection still. First, the liquid being distilled is placed in the heating chamber. Heat is applied until the liquid begins to boil and vaporize. The vapor rises into the condensing tube, where a cold liquid, usually water, runs along the outside of the tube to quickly reduce the temperature of the vapor. As the temperature declines, the vapor reduces back into a liquid state and accumulates in the collecting still. The resulting liquid contains an isolated product of the constituents from the original liquid that vaporize at the temperature of the heat source.
Simple distillation has many disadvantages. Because it takes place in an “open system” (or a system using atmospheric pressure), the liquid must reach very high temperatures before vaporization will occur. Since many volatile aromatic compounds are heat sensitive, damage to the structure and quality of the product may occur. Additionally, it is difficult to get a pure yield because residues of other constituents may vaporize at temperatures outside of their normal boiling point and contaminate the product.
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