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Technology
By-products
Technological evolution
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 (as it is shown in the diagram) 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.
A detailed comparison of results obtained from a two phases extraction and a three phases extraction is represented in the following table. The study has ben made with different varieties of olives whose composition was: moisture (48 - 51 %), oil (19 - 23 %).
| Two phases extraction | Three phases extraction | ||
| Oil extraction capacity |
86% a
|
85% a
|
|
| Pomace | |||
|
|
Quantity (kg/100kg of olives) |
72.5 a
|
50.7 b
|
| Moisture ( %) |
57.5 a
|
52.7 b
|
|
| Oil (%) |
3.16 a
|
3.18 a
|
|
| Oil (% dry material) |
7.44 a
|
6.68 a
|
|
| Oil (kg/100kg of olives) |
2.28 a
|
1.60 b
|
|
| Dry pomace (kg/100kg of olives) |
30.7 a
|
23.9 b
|
|
| Vegetable waters | |||
| Quantity (liters/100kg of olives) |
8.30 a
|
97.2 b
|
|
| Oil (g/liter) |
13.4 a
|
12.6 a
|
|
| Oil (kg/100kg of olives) |
0.14 a
|
1.20 b
|
|
|
Dry residual (kg/100kg of olives) |
1.20 b
|
8.3 b
|
|
| Oil in by-products (kg/100kg of olives) |
2.42 a
|
2.80 a
|
|
|
Values followed by identical
letters show that they are not statistically different to P<
0.05.
|
|||
| Study by Amirante P., Di Renzo G.C., Di Giovacchino L., Bianchi B., Catalano P., 1993, Olivae n°48, 43. | |||
Discontinuous extraction is an ancestral procedure 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.
