Olive presses and mills explanation


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Mill and Press Facts
How Olives are turned into oil

Steps to olive oil making once you've grown and picked the olives:

1. Cleaning the olives.
2. Grinding the olives to paste
3. Mixing to increase olive oil yield
4. Separating the oil and water from the fruit (pomace)
5. Separating the oil from the water
6. Processing the oil, further extraction
7. Storage and Bottling considerations
8. Tasting and rating your oil

Buying Mills and Presses

3. Mixing The Olive Paste - Malaxation
	Mixing or Malaxation for 20 to 40 minutes allows small oil droplets to combine into bigger ones which can be removed in the next step. It is an absolutely necessary step. The paste is often heated to 28 degrees centigrade during this process. The most common mixer is a horizontal trough with spiral mixing blades.

Mixing Times
Longer mixing times increase oil yield and help the oil pick up minor components which can improve flavor. But longer mixing allows oxidation which decreases shelf life. The new Pieralisi "Genius" system uses closed mixing chambers which are filled with inert gas during the mixing cycle, thereby allowing increased yield and flavor without the danger of oxidation.
Advantages of longer mixing better yield oil picks up minor chemical constituents

	Disadvantages of longer mixing more oxidation shorter shelf life higher acidity and peroxides

Heating

Heating the olive paste will decrease viscosity and improve water oil separation. This increases yield. Heating speeds oxidation and enzymatic breakdown of the paste.

Advantages

better yield

Disadvantages

more oxidation
shorter oil shelf life

Using Inert Gasses

To discourage oxidation, mixing tanks can now be ordered with covers which contain an inert gas such as CO2 or Nitrogen over the paste. Mixing chambers kept under a vacuum will do the same but cannot remove as much oxygen as an inert gas blanket.

Advantages

better yield
oil picks up minor chemical constituents

Disadvantages

cost of inert gas, vacuum equipment
more complex equipment, slightly more cost

Pieralisi Genius enclosed, automated mill

4. Separating the Oil and Water From the Olive Paste (pomace)


Lever Olive Press
	Of historical interest only, the olive paste was put on round mats or in burlap bags, stacked and squeezed with a long lever weighted with stones.
Disadvantages low pressure bulky discontinuous process

Screw Olive Press
	Of historical interest only. Here being used with the "sacceto" type bags for holding the olive paste. Twisting the screw
Disadvantages low pressure discontinuous process

Hydraulic Olive Press

hydraulic olive oil press

Like a hydraulic car jack, the piston squeezes the paste which has been applied to stacks of filter like discs. Press is on the left in the picture

Advantages

limited investment
simple and reliable machinery
low energy consumption
pomace has a low moisture content
Tolerates rocks, sand without wear
no water is added, minimal vegetable water disposal

Disadvantages

labor intensive
Decomposition of materials left on mats if not properly cleaned and stored can produce chemicals responsible for winey and fusty defects
Discontinuous process

Centrifugal Decanter

olive oil decanter - how do you make olive oil

Spins the olive paste in a horizontal drum; the heavier flesh and pits goes to the outside and the water and oil is tapped off from the center.

Advantages

compact machinery - one decanter can take the place of several presses
semi continuous and automated
limited labor

Disadvantages

expensive
more technical labor required
may consume hot water
high energy consumption
pomace may end up moist
greater amount of vegetable water to be disposed of
reduced antioxidants due to added water
subject to wear from rocks, grit

Advanced Dual Phase, Triple Phase Centrifuge

Same as above but some of the vegetable water is recycled to extract more from the pomace. Water, oil and pomace simultaneously removed in single step

Advantages

highest percent oil extraction
dry pomace
less or no water added
less loss of antioxidants
vegetable water disposal 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. see ref

Disadvantages

expensive
more technical labor required
high energy consumption
pomace may end up moist
greater amount of vegetable water to be disposed of
reduced antioxidants due to added water
subject to wear from rocks, grit

Percolation - Sinolea

sinolea olive oil separator

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

Advantages

higher polyphenol content of oil
low temperature method
automated
low labor
oil/water separation step is not needed
low energy requirement

Disadvantages

often must be combined with one of the above methods to maximize oil extraction which requires more space, labor, etc.
large surface areas can lead to rapid oxidation
Sale of future machines currently outlawed in European Union due to difficulty with cleaning such large surface areas.

Co-adjuvants

Materials added to to increase yield, extract additional oil from pomace:

Types

enzymes
talc
steam
hexane, other solvents
alkali

Disadvantages

not used in better quality oils
Disputed status as far as labeling requirements

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