General Manufacturing Methods
Grinding of Olives to Paste
Stone Olive Mills
Stone rollers or wheels roll in circles on a slab of granite to grind the olives into a paste.
- can be adapted to olive and pit size to optimise paste characteristics
- doesn't cut the skin, releasing less chlorophyll so less bitter oil
- formation of larger size drops of oil, minimizing mixing times
- paste isn't heated
- stone is difficult to clean
- green olives will prolong grinding time
- discontinuous process - time consuming
- high labour cost
A hammer mill has swinging arms which through centrifugal action push the olives into the sides of a rotating chamber, similar to a home garbage disposer. The mill may have one to several hammers.
- high throughput
- Tolerates debris such as rocks and grit
- know, perfected technology
- extracts more phenols so oil has longer shelf life
- may form emulsion which impedes oil - water separation
- organoleptic characteristics affected - oil can have bitter, stronger, spicy taste due to more phenols
- wear and tear of metal parts
- oil paste may heat up
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 centre.
- Compact machinery - one decanter can take the place of several presses
- semi continuous and automated
- limited labour
- more technical labour 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
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.
- higher polyphenol content of oil
- low temperature method
- low labour
- oil/water separation step is not needed
- low energy requirement
- Often must be combined with one of the above methods to maximize oil extraction which requires more space, labour, etc.
- Large surface areas can lead to rapid oxidation