Olive oil extraction generates several by-products that can be used to feed animals, particularly the cakes and pomaces obtained from the extraction process, and leaves and other residues resulting from the cleaning operations. The young shoots coming out from the base of the tree can be browsed by sheep and the olives themselves can be eaten by pigs in extensive systems, such as those producing the Jamón ibérico in Spain.
The nature of olive oil cakes and by-product depends on the processing method. Mechanical extraction of olive oil yields about 33% (with 24.3% water) crude olive oil cake while solvent extraction yields 25% exhausted olive oil cake and 17% water. The yield for fat olive oil cakes is about 40-55% in the 3-phase extraction process, and up to 80% in the 2-phase process (as olive oil cake still contains water) (Sansoucy et al., 1985; Molina Alcaide et al., 2008). After oil extraction, the crude or defatted cake may be de-stoned. The defatted, de-stoned oil cake is the most frequent product. The average yield of de-stoned olive cake is about 50% but varies greatly (Eraso et al., 1978). The Acapulco or Enfida process consists in de-stoning olives before extraction, resulting in a crude or defatted olive pulp (Nefzaoui et al., 1978).
The products of olive oil manufacture are the following:
Crude olive oil cake obtained by mechanical extraction. This product contains residual oil and stones.
Exhausted or defatted olive oil cake, obtained by mechanical and solvent extraction. This product contains stones and less residual oil than the previous one.
Crude olive oil cake without stones, obtained by mechanical extraction and de-stoning. This product contains residual oil and no stones.
Exhausted or defatted olive oil cake without stones, obtained by solvent extraction and de-stoning. This product contains little residual oil and no stones.
Olive oil pulp, obtained after stone removal followed by mechanical extraction.
Exhausted olive oil pulp, after stone removal and solvent extraction.
Olive oil vegetation water (“black water” or alpechin), obtained by centrifugation or sedimentation of the oil. This sugar-rich product is sirupy, black and bitter with a distinctive odour due to polyphenols and other substances. It can be (partially) dried, resulting in a molasse-like product.
98% of the production of olive oil is done in Mediterranean countries. Spain, Italy and Greece are the main producers (75% of the total production). The demand for olive oil has increased a lot since the mid-1990s and olive oil production in 2009 was almost twice (2.91 million tons) as that of 1995 (1.65 million tons) (FAO, 2010).
Olive-mill vegetation waters are regarded as a severe environmental problem because of their high organic content consisting in poorly-degradable phenolic compounds that are both antimicrobial and phytotoxic (Ramos-Cormenzana et al., 1995). However, modern olive oil manufacturers usually use 2-phase centrifugation extraction processing methods that do not produce olive oil vegetation water.
As the cake turns rancid rather quickly and may become completely unpalatable and even harmful to animals, it must be preserved either by drying or ensiling.
Polyphenols and tannins
Olive oil cakes obtained from the 2-phase extraction process contain tannins, but they do not seem to have toxic effects on livestock. Sheep appear to be more sensitive to olive cake tannins than goats (Yanez-Ruiz et al., 2007).