Effect of Harvest date on the yield and quality of the essential
oil of peppermint. Can. Journ. Plant Science 73, Court W A, Roy R C and Pocs R (1993)

Improvements in Field Distillation of Peppermint Oil, Station Bulletin 525, Hughes A D (1952)

Peppermint oil yield and composition from mini and industrial
distilleries, Journ. of Herbs, Spices and Medicinal Plants, Mitchell A R and Crowe F J (1996)

Agronomic factors affecting the yields and essential ol content of peppermint. Int. Symp. on Medicinal
and aromatic Plants, Piccaglia R, Dellacecca V. Marotti M, Giovanelli E, Palevitch (ed) and Putievsky (ed) (1993)

Essential Oils Processes and Formulations Hand Book. Delhi, Engineers India Research Institute, 2003, xiv, 274 p., figs., tables, (pbk). ISBN 81-86732-39-X. (https://www.vedamsbooks.com/no32281.htm)

Book Reviews Index - Distillation, Extraction, Steam, Water, CO2, EOs, Extracts, Absolutes, Concretes, Tintures

Distillation Operation

Still design and construction has been approached from as many angles as there are practitioners, and although most follow a few basic rules, the hardware involved, the match between components and the logistics of operation are usually specific to the site concerned.

Articles and Reports>

Steam Distillation

Different processing methods are required to extract essential oils from different plants. Most oils are extracted using steam distillation, during which the plant material is permeated with steam. As the plant tissues break down, the essential oils and water vapor are released, then collected and cooled. The volatile essential oil condenses, separates and is easily isolated.

In this process the steam is prepared in a separate chamber and piped into the tank. This is more expensive than the other methods. This is especially good for plant materials with high boiling point oils. In this method the temperature and pressure can be increased for certain oils.

The rate of distillation and yield of oil are high and the quality of the oil is good.

Articles and Reports>

Water Distillation

This is the simplest and usually cheapest distillation method. The plant material is immersed in water and boiled. The steam and oil vapour is condensed and the oil is separated from the water. This method is suitable for flower blossoms and finely powdered plant material.

The distillation temperature should be about 100°C. Care needs to be taken to prevent the plant material being damaged by contacting the overheated still walls. The pressure in the still should be atmospheric. The distillation time depends on the plant material being processed. Prolonged distillation produces only a small amount of extra oil, but does add unwanted high boiling compounds and oxidation products.

Articles and Reports>

Solvent Distillation

Essential oils can be extracted using solvents. Hydro-distillation is not suitable for various products like delicately odoured oils. There are three main ways that this can be performed.

Solvent extraction is used when the odorous properties of delicate flower and plant material would be altered or destroyed by steam or water distillation or when a plant, for instance rose absolute and jasmine contains very little oil, making steam or water distillation impractical.

Solvent extraction produces a concrete which in turn is refined into an absolute. To produce a concrete, the plant material is gradually saturated with a hydrocarbon solvent. The solvent dissolves the plants constituents including essential oils, fatty acids and waxes. After the solvent is distilled off the remaining constituents make up the concrete. The essential oil is extracted from the other constituents with alcohol. The fatty acids and waxes are not alcohol soluble so they're left behind. A secondary distillation then removes the alcohol, leaving the absolute oil behind.

Articles and Reports>

Supercritical CO2 Extraction (SCFE)

Supercritical carbon dioxide extraction uses carbon dioxide under extremely high pressure to extract essential oils, fragance products, herbal extracts and spice extracts. The organic material is placed in a stainless steel tank and, as carbon dioxide is injected into the tank, pressure inside the tank builds. Under high pressure, the carbon dioxide turns into a liquid and acts as a bonding agent to extract the essential oils from the plants. When the pressure is decreased, the carbon dioxide returns to a gaseous state. Because Carbon Dioxide is relatively inert, contamination free process.

Many carbon dioxide extractions have fresher, cleaner, and crisper aromas than steam-distilled essential oils, and they smell more similar to the living plants. Scientific studies show that carbon dioxide extraction produces essential oils that are very potent and have great therapeutic benefits. This extraction method uses lower temperatures than steam distillation, making it more gentle on the plants. It produces higher yields and makes some materials, especially gums and resins, easier to handle. Many essential oils that cannot be extracted by steam distillation are obtainable with carbon dioxide extraction. In the future, many botanicals that are not now available may possibly be obtained through carbon dioxide extraction.

Source: A Complete Guide to Understanding and Using Aromatherapy for Vibrant Health & Beauty, 1995 -Roberta Wilson- ISBN 0-89529-627-6

Supercritical Fluid Extraction can be used with the following natural products..