oil for english episode 4 >> separating


episode 4 >> SEPARATING THE OIL FROM THE VEGETABLE WATER AND SOLIDS

The next step is to separate the oil from the water and the paste. This can be done (or was historically done) in the many ways described below. Most systems fall into two main categories: presses and centrifugation. Nowadays, centrifuges are used almost exclusively, aside from old operations.

Historically, olive paste was put on round mats or in burlap bags, stacked, and squeezed with a long lever weighted with stones, or via a twisting screw. These presses were bulky and inefficient, since the pressure was low and the process discontinuous. In addition, the mats or bags were nearly impossible to clean. The olive paste in this photo was being squeezed in “sacceto” bags.

Because it was not possible to extract all the oil in the “first press”, hot water was added to the pomace to help release additional oil, and a second press (or several) was done, hence the terms “First Press” and “Cold Press”, which are now pretty much obsolete, even though still widely used improperly for marketing reasons.

This is somewhat similar to a hydraulic car jack: a piston squeezes the paste that has been applied to stacks of disk-like filters.

Advantages

  • Requires a limited investment.
  • It is simple and reliable machinery.
  • The energy consumption is low.
  • The resulting pomace has a low moisture content.
  • It tolerates rocks and sand without wear.
  • No water has to be added and there is minimal vegetable water disposal.

Disadvantages

  • It is very labor intensive.
  • Decomposition of materials left on mats, if not properly cleaned and stored, can produce chemicals responsible for winey and fusty defects.
  • It is a discontinuous process.
  • An additional step is needed to separate the oil from the vegetable water.
  • There is more exposure to oxygen resulting in more oxidation and a higher level of peroxides.
  • The shelf life of the oil is shorter.

 

Centrifugal Decanters (Three-Phase)

These days, modern facilities all use a centrifuge-based system of extraction, also referred to as horizontal decanters. The traditional centrifuges (still commonly used) are three-phase: they spin the olive paste in a horizontal drum; the heavier flesh and pits go to the outside and the water and oil are tapped off separately from the center.

 

Advantages

  • The machinery is compact – one decanter can take the place of several presses.
  • They are semi-continuous and automated.
  • The amount of labor required is limited.
  • There is no need for an oil/water separation step.

Disadvantages

  • They are expensive.
  • More technical labor is required.
  • They may consume hot water.
  • The energy consumption is high.
  • The pomace may end up moist.
  • As water has to be added to the process, a greater amount of vegetable water has to be disposed of.
  • There is a loss of polyphenols due to the added water.
  • They are subject to wear from rocks, sand, and grit.


Advanced Dual Phase, Triple Phase Centrifuge

These are similar to the centrifugal decanter described above, but some of the vegetable water is recycled to extract more from the pomace. The water, oil, and pomace are simultaneously removed in a single step. This is the most modern machinery available at this time.

Advantages

  • They have the highest percentage of oil extraction.
  • In three-phase systems, the pomace is dry and readily usable.
  • There is no need for an oil/water separation step.
  • Less or no water needs to be added.
  • The oil has more polyphenols and a longer shelf life.
  • The vegetable water disposal is less of a problem.
  • Olive oil from two-phase centrifugation systems contains more phenols, tocopherols, trans-2-hexenal and total aroma compounds and is more resistant to oxidation than oil from three-phase ones and from hydraulic presses.

Disadvantages

  • They are expensive.
  • More technical labor is required.
  • The energy consumption is high.
  • They are subject to wear from rocks, sand and grit.
  • The oil has more polyphenols so will be bitterer.

There are different advantages and disadvantages to two-phase vs. three-phase systems, in particular in terms of waste disposal.

Percolation – Sinolea

Rows of metal discs or plates are dipped into the paste; the oil preferentially wets and sticks to the metal and is removed with scrapers in a continuous process. This is not very commonly used and sale of future machines is currently outlawed in the European Union due to the difficulty of cleaning such large surface areas.

Advantages

  • The polyphenol content of the oil is higher.
  • It is a low temperature method.
  • It is automated.
  • The labor requirement to operate the machine is low.
  • There is no need for an oil/water separation step.
  • The energy consumption is low.

Disadvantages

  • It often must be combined with one of the above methods to maximize oil extraction; this, of course, requires more space, labor, and expense.
  • The large surface area can lead to rapid oxidation.

 

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