GrasasYaceites 1-57. pdf

5. SELECTIVE FILTRATION OR PERCOLATION
This system consists in the extraction of the free
oil that appears after the milling and kneading
steps. The rest of the oil has to be extracted by
pressing or centrifugation systems. The selective
filtration is based on the differences in surface
tension between the liquid phases of the olive paste
and a stainless steel plate. Oil has lower surface
tension and when the metal surface comes into
contact with the olive paste it is coated mainly with
a film of oil.
Based on this principle described at the end of
twentieth century by Miguel Prado y Lisboa,
Marques de Alcapulco, several machines were
developed. At present there are two different
systems: Thermoextractor Palacín similar to the
original ‘Acapulco-Quintanilla’ and the Alfin system
available as Sinolea. When the extraction starts, the
GRASAS Y ACEITES
, 57 (1), 
ENERO
-
MARZO
, 25-31, 2006, 
ISSN
: 0017-3495
27
OLIVE OIL EXTRACTION AND QUALITY

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oil amount is high and the waste water is extracted
in a small percentage, however as the extraction
goes on the waste water and its dissolved solids
content raises and the oil extracted is lower. For this
reason, the residence time of olive paste in the
extractor should be less than 30 minutes. In these
conditions between 20-50% of oil contained in the
olive paste can be extracted, with variable waste
water content depending on the paste difficulty. The
main advantages of selective filtration are:
– Virgin olive of high quality considering sensory
and chemical indexes
– A higher amount of oil is obtained
– The efficiency of the plant is improved since
the extracted oil does not pass through the
horizontal centrifuge.