Hydrodistillation of aromatic plant materials in Clevenger apparatus gives essential oils. In this method, the material is completely immersed in water, which is boiled by applying heat by direct fire, steam jacket, closed steam jacket, closed steam coil or open steam coil. Hydrodistillation is performed under atmospheric pressure at the boiling temperature about 100 °C, The main characteristic of this process is that there is direct contact between boiling water and plant material. When the still is heated by direct fire, adequate precautions are necessary to prevent the charge from overheating. When a steam jacket or closed steam coil is used, there is less danger of overheating; with open steam coils this danger is avoided. But with open steam, care must be taken to prevent accumulation of condensed water within the still. Therefore, the still should be well insulated. The plant material in the still must be agitated as the water boils, otherwise agglomerations of dense material will settle on the bottom and become thermally degraded. Using the clevenger extractor, mainly mono and sesquiterpenes are extracted, diterpenes are less volatile and hence not very likely but traces may be obtained in the mixture.

I can't take my answer from your answer, I know what is the celevenger...

While extracting essential oil by hydrodistillation using Clevenger apparatus, the water boils at 100°C that cause to ascend the vapour mixture (steam and extractible oil) and yield essential oil, but prolonged heating at high temperature may cause changes or decomposition in thermolabile compounds. To prevent this, as soon as the water starts boiling temperature of heating mantle should be brought down to 60oC. Strict control over the temperature is essential. This implies for all soft tissue plant materials including those mentioned by you.

Thank you for your attention Doctor Tripathi, your answer is so useful.

Sincerely yours.

ok so let me get this straight, as soon as the water starts to boil (at 100oC) I should directly lower down the temperature to 60oC, right?

One more thing, I have discovered that the smell of the oil is filled with the smell of cooked plant which is a very bad smell, given the fact that I am working with dry lavender flowers. My question is, for how long should I run the procedure of hydrodistillation ? is 3h enough ?

let me get this straight, as soon as the water starts to boil (at 100oC) I should directly lower down the temperature to 60oC, right?

One more thing, I have discovered that the smell of the oil is filled with the smell of cooked plant which is a very bad smell, given the fact that I am working with dry Ocimum leav@es. My question is, for how long should I run the procedure of hydrodistillation ? is 3h enough ?

Clevenger apparatus work on the principle of hydrodistillation for extraction of essential oils which are a type of voltaile oils used as a pharmaceutical importance.