Size Reduction

To hasten the release of oil from the cells, it may be necessary to grind the material. However, care should be taken to avoid fine grinding. Fine particles will pack tightly in the still, making it difficult for steam to pass through the bed uniformly. This will encourage channeling of the steam. Coarse grinding is more advantageous in such cases.

In some plant products such as black pepper, merely passing through a roller mill once or twice will be sufficient. The berry will flatten into a flake, and cells will open up.

In hard materials, such as rhizomes, an initial coarse grinding using a hammer mill or a pin disk mill may be required before passing through a roller mill. In a hammer mill, due to the heavy impact, the temperature rise of the material can be significant. Because of the distribution of the points of impact, pin disk mills produce less heat. In cardamom, the essential oil is in the seeds, but they are covered by a husk. So the capsules are led to a loosely adjusted plate mill, where the husks are opened without damaging the seeds, which are then separated from the husks. Only the seeds are taken for steam distillation.

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