Olive oil is commonly extracted using a millstone.
Olive oil presses have been around for thousands of years, with the ancient Greeks getting credit for creating the first presses nearly five millennia ago. Most extraction machines have two stages: one for crushing olives to separate the oil and water from the solid part of the olives, and one for separating the oil from the water.
Crushers
Once olives are cleaned and ready to be processed, they must be ground into a paste. Different mechanisms have been used to do this, including large stones and metal grinders. Millstones are commonly used to crush olives. These large stones roll around on a flat granite slab, with the benefit being that the skins of the olives are not broken and less chlorophyll is released.
An alternative to the large grinding stones is to use a metal tooth grinder. This contraption uses centrifugal force to fling olives from the center, knocking them against metal teeth on their way to the edge.
Malaxers
Once the olives are crushed into a paste, they are then subject to a mixing process called malaxing. This is when the paste is stirred in a trough by a metallic spiral in order to combine smaller oil droplets together into bigger drops. Some malaxers include heaters, but heating the paste reduces the quality of the oil.
Separators
Most modern machinery uses centrifugal force to separate the oil from the water and solid paste. Some machines separate the liquids from the solids, then they further separate the liquid from the water. Older machines have a press that does this, which is where the term "first press" comes from on some bottles of oil in a supermarket. If the crushing and separating process is performed at a temperature under 27 degrees C, the label "cold pressed" may be used on the bottle's label, according to the laws of the European Union.
Filters
Some extraction machines include a filtration system that removes debris from the olive paste. This debris is mainly composed of twigs and leaves from the olive trees, in addition to any final pieces of olive paste that were not caught by the centrifugal separator.
Tags: from water, centrifugal force, from olive, have been, into paste