The oil bears the name of the plant from which it is derived; for example, rose oil or peppermint oil. Such oils were called essential because they were thought to represent the very essence of odour and flavour.
Essential oil is a natural product extracted from a single plant species. Not all plants produce essential oils, and in the plants that do, the essential oil may be found in the roots, stems, leaves, flowers, or fruits. Essential oils do not feel oily; they are called "oils" because they contain the oil-soluble chemicals in the plant (usually 100 to 200 chemicals per essential oil). This complex chemistry gives essential oils their therapeutic properties.
Let's look at where essential oils come from and how they get in the little bottles you purchase. Did you know that it takes approximately 1 ton or 2,000 pounds of rose petals to get 1 pound of essential oil? That's a lot of plant material, wouldn't you agree? Have you ever purchased or looked at the price of rose essential oil? Prices vary because of many factors. However, paying $200 for 5 ml or one teaspoon of rose essential oil is not uncommon.
Since there are often various plants, we always need to know which plant we are referring to. It is particularly important when using essential oils for therapeutic purposes since there are more than one species of the same plant. One example of this is lavender. True lavender that we might use for calming is Lavandula angustifolia. Another lavender species with very different chemical properties and not known for calming is Lavandula latifolia. For simplicity's sake, you'll see common and botanical names used throughout this course. The botanical name will always be used when referring to specific therapeutic properties. And once the botanical name is identified, you'll most often see the common name. Before we examine how we obtain essential oils, let's look at some plants to see where the essential oils come from. The amount of essential oils produced by different plants is quite variable. Many plants' essential oils are readily extracted, while others are too fragile to withstand this process. Still, others don't produce enough essential oil to be cost-effective for steam distillation.
Some plants are dried and then distilled, while others are distilled while fresh. You don't need to know the specifics of each plant at this point. I want you to know that you can readily find this information in numerous essential oil reference books. I want to point out a few that you might be familiar with, and you already know that rose essential oil is from flower petals. Lavender, Lavandula angustifolia, is from the flowering tops and stocks. Frankincense, Boswellia carterii, is from the resin; think of it like a sap. Anise is from the seed Pimpinella anisum. Basil is from the leaf. Ginger from the rhizome, grapefruit from the rind. Hmm, Cedar Wood, any idea? That's right, the wood.
Steam distillation and expression are the primary ways we obtain essential oils. Most essential oils are obtained by steam distillation, so I'll start there. The harvested plant material is placed in a large vessel. So notice the second vessel, a heat source produces steam passed through the vessel holding the plant material. This steam ruptures and loosens the essential oils from the plants and allows the precious volatile molecules to rise to the top of that vessel with the steam. Volatile means readily vaporising or dissipating. The steam and volatile essential oil molecules pass through a cold condenser. As the condenser cools the steam back into the water, it moves with the essential oils to the final vessel. Here, the essential oils rise to the top. So picture how oil and water separate.
The essential oils are now easily extracted from the remaining floral water; as you can see, they're on top of the floral water. It's worth noting that the remaining floral water also has therapeutic properties. You may be familiar with some of these, such as rose water or orange water. These floral waters are also known as aromatic water hydrosols or hydrolats. Essential oils and citrus fruits are held in the rinds and are typically extracted in a process unique to them, known as an expression or cold pressing. Although these fruit rind essential oils can be steam distilled, it's much more common to extract them with the expression method. Please think of how lemon or orange squirt from the rind when you peel it or when you zest it.
That's the essential oil. Commercially produced essential oils are obtained through a mechanical process or puncturing of the rinds. This rind material is then centrifuged and separated from the essential oil. No heat is used, so no chemical changes occur, as in steam distillation with a heat source. So the essential oil will smell identical to the plant; this isn't the same as when essential oils are obtained with the heat source. So, when scenting a grapefruit or lemon essential oil bottle, notice the fruit's aroma.
Most importantly, essential oils are typically made through steam distillation or extraction. Various parts of the plant hold essential oils, and you should describe essential oils by their botanical name to ensure you are referencing or using the right plant essential oil.
Try zesting a lemon, or crushing a herbal leaf, such as basil, or a flowering top, such as lavender, with your fingers to release the essential oil aroma.
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Studied Aromatherapy: Clinical Use of Essential Oils. Offer by The University of Minnesota.
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