Cold Pressing Extraction

No heat is involved in this process. In the case of citrus fruits, essential oils are found in the large cells of the flavedo, near to the surface of the fruit. These cells are easily ruptured by compression of the peel or when the peel is mechanically grated or abraded. Expression is normally only used for citrus fruits. Most nut and seed oils are also extracted using a "cold pressed" method but here oil is forced from the material under high mechanical pressure and generally produces good quality oil. Three different ways are used to accomplish it:

1. Sponge Method: - The fruit is cut in half and the pulp removed. It is then soaked in warm water for a short time in order to allow the pith to absorb water, which renders it softer and more elastic. The peel is exposed to the air for several hours. After this the fruit is turned inside out and a sponge placed next to the rind. The fruit is then compressed, which causes the oil cells to rupture, releasing the oil which is absorbed by the sponge. The sponge is periodically squeezed into a collecting vessel.

2. Eculle a Piquer Method: - This form of expression extraction is used mainly to obtain citrus essential oils, and is a little less labor intensive than that of the sponge method. This more modern way of essential oil extraction is referred to as the écuelle a piquer process where the fruit is placed in a device and rotated with spikes on the side puncturing the oil cells in the skin of the fruit. This cause the oil cells to rupture and the essential oil, and other material such as pigment, to run down to the center of the device, which contains a collection area. The liquid is thereafter separated and the oil is removed from the water-based parts of the mixture and decanted.

3. Machine Abrasion: - This involves feeding the fruit into a rotating drum, which is lined on the inside with spikes. As the drum rotates the spikes strip off the peel which is then carried in a stream of water into a centrifugal separator. This rotates at high speed, generating centrifugal force, which separates the essential oil from the other components. The whole process has to be done quickly to prevent enzymatic action causing adulteration while the essential oil is in contact with other contents of the oil cells.