The ancestral procedure is the discontinuous extraction that only distinguishes two phases by pressing or centrifugation. The liquid phase is filtered later in order to obtain oil. In this case the by-product is a plastic paste which has the advantage of avoiding the production of vegetable waters. However, although it is more ecological, this technique provides a lower yield and this is not always seen as an advantage for the main producing countries.
The most common industrial processing method is a continuous extraction system with two centrifugations (first horizontal and then vertical). Vertical centrifugation may be in three phases obtaining oil, pomace and vegetable waters or in two phases, in this case there is no water injection or little water obtaining oil an a plastic paste.
Pomace is the solid residual derived after first pressing or centrifugation (a little of olive, pieces of nut, etc.). It may be used for livestock feeding or going through a chemical extraction with the purpose of producing olive-pomace oil.
Vegetable waters are the liquid phase obtained as a result of centrifugation. They are aboundant in the three phases extraction method due to the water injection made to the paste before centrifugation. As vegetable waters still contain oil, they are treated a second time in order to get the maximum amount of oil. However, since this is a combination of water and fat, it is difficult to recycle them. Vegetable waters are highly polluting and negatively affect underground waters. The most serious ecological problem in olive oil production is the recycling of vegetable waters.
The procedure introduced in previous scheme is the most widely used in intensive production areas. It dates back to the seventies and eighties. The main disadvantages of this process are the huge amount of water needed and therefore the production of vegetable waters with the resulting pollution.From 1991 there are new industrial techniques of continuous extraction. They reduce the production of vegetable waters by obtaining a much more humid pomace that can be moisturized and used later. This process does not need much water. It is being more and more widely used.
The new innovation is the combine of the traditional three phase and the modern two phase technology with the new extraction technology two phase and half or with limited water injection. It’s consist for a little water injection with the production of vegetable waters in limited quantities.
A detailed comparison of results obtained from a two phases extraction and a three phases extraction and the two phase and half is represented in the following table.
|Three phases with a little water injection or Two phases and half