Expression of Citrus oils

Expression is also know as Cold-press Extraction or Scarification and is used for citrus peels in particular. This method uses only mechanical pressure (no heat is used)  for extraction of oil. The whole fruit is pierced to rupture the essential oil containing sacs. this causes the oil and color pigments to be released. The whole fruit is then pressed to squeeze out the juice and oil which is then centrifuged to separate out the oil. A variation to this process is to remove the peel from the fruit before the oil is expressed.

Why Expression?

Some essential oil like lemon oil, bergamot oil, orange oil cannot be extracted without decomposition and are usually obtained by Expression or by other mechanical means. Most nuts and seed like groundnut oil, mustard oil etc are also extracted using this method. The oil is forced to come out of the material under high mechanical pressure which produces good quality oil. Since no heat is involved the oil extracted smells very close to the original plant. In case of citrus fruits like lemon, bergamot, orange etc. the rind is squeezed to obtain the essential oil they secrete.

Methods of Expression

 

There are different ways to expression or cold pressing. One method that was practiced years ago is the spugna or sponge method. In this method the citrus fruit is halved and the pulp is removed. The oil is removed from the peel by pressing the peel against a hard object of baked clay which is place under a large sponge or by inverting the peel into the sponge. The oil emulsion is absorbed by the sponge. The sponge is then squeezed and the oil emulsion collected into a container.

SCODELLA

A second method know as the scodella method uses a shallow bowl with a hollow central tube similar in shape to a shallow funnel. The bowl is covered by blunt points onto which the whole citrus fruit is rolled by hand with pressure until the oil glands burst. The mixture of essential oil and aqueous cell content dribbles down the hollow tube into a container. The oil is then decanted and collected.

These processes are very slow and as a result machines have been designed for expression of citrus oils (Machine Abrassion).

PELATRICE METHOD OF EXPRESSION

In Pelatrice process the fruit are fed from a hopper into the abrasive shell. The fruits rotate againt the shell by a slow moving screw which help rupture the oil glands releasing the oil-water emulsion. The fruit is then pressed under rollers covered in abrasive spikes which burst the remaining oil cavities. The oil-water emulsion is washed away by a fine spray of water. The emulsion collected passes through centrifugal seperators which remove the solids and the water yielding pure essential oil.

SFUMATRICE EQUIPMENT

In Sfumatrice process there are metallic chains that are drawn by two horizontal ribbed rollers. The peel passes through these rollers during which it is pressed and bent to release their oil. The rollers are washed by a fine spray of water. The oil-water emulsion collected is then passed through centrifugal separators so that purified oil can be produced.