H2o

adequate for the material to move freely in boiling water, thus avoiding localized overheating and subsequent charring of the material. The water is boiled under direct fire or by steam jacket or closed steam coil. It may be necessary to add more water as the distillation proceeds to prevent any dry material from being exposed to direct heating. The vapor is condensed and oil separated from water, taking advantage of their mutual immiscibility and difference in specific gravity. This method is normally used where the raw materials tend to agglutinate and form large compact lumps through which steam cannot penetrate. Water distillation suffers from the following drawbacks (Guenther, 1972):

• Water distillation is a slow operation. It requires more number of stills, more space, and more fuel, and is the least economical of the three techniques.

• It is difficult to exhaust the material completely. High boiling and somewhat water-soluble components cannot be completely recovered from the large quantity of water. The distilled oil, therefore, will be deficient in these components.

• Certain components, such as esters and aldehydes, are likely to deteriorate under the prolonged contact with boiling water.

• The exhausted plant material forms a slurry with water that is difficult to handle and dispose.

• If the deoiled material is required for further processing, additional dewatering and drying steps would be necessary.

• Boiling water may dissolve some of the nonvolatile active components in the plant material, which are lost during dewatering. The oleoresin from the deoiled material could, therefore, be of inferior quality.

However, the simplicity of the method makes it suitable for small-scale distillation of essential oils.

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