- Simplest and oldest process available for obtaining essential oils from plants.
- Hydro distillation differs from steam distillation mainly in that the plant material is almost entirely covered with water in the still which is placed on a furnace.
- Care should be taken during distillation of powdered herbs, as they tend to settle on the bottom of the still and get thermally degraded.
- Also, for plant material that tends to form mucilage and increase the viscosity of the water, the chances of charring are greater.
- As the plant material near the bottom of the still comes in direct contact with the fire from the furnace, it may char and thus impart an objectionable odor to the essential oil.
- The prolonged action of hot water can cause hydrolysis of some constituents of the essential oil, such as esters.
- Heat control is difficult, which may lead to variable rates of distillation.
- The process is slow and distillation times are much longer than those of steam distillation.
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