• Katja

Harvesting Olives 6 - Oil quality and centrifugation

Updated: Jan 19, 2020

We've popped into the office to check the paperwork and then we're off for a coffee while the olives get churned. .

People often ask about low-grade olive oil. As explained in my previous post, lower quality or less tasty oils can be the result of higher temperatures during malaxation, aging, over-ripe olives, etc. Other factors which can lead to a bitter taste in olive oil include fruit fly infestation, delays between harvesting and extraction, fungal diseases in the fruit, and careless extraction methods. . But there's also some very underhand practices that go on in the sale of olive oil in unregulated mills or once the oil has left the mill and is being 'transported' and stored. This means that you may think you're buying extra virgin oil when in fact you're not. . Talc is sometimes used to process difficult fruit or to increase yield with some types of fruit. Other co-adjuvants solvents can be used to increase the yield. . Possible additional processing steps include: refining the oil to reduce its acidity and improve flavour (in defective oils) by alkali (chemical reaction with an alkali–caustic soda); steam processing; bleaching the oil to reduce chloroph. . Lastly, a common fraudulent practice is to mix refined cheaper non-olive oils with olive oil. That's the easiest trick in the book -- retailers command higher prices for oil that's only part olive oil. . I'm not sure what buyers can do apart from purchasing oil from a trusted source or a label that you know comes from the mill straight to the shop. Doing a bit of research should pay off. . In case you're wondering, the 3rd photo is Rafael doing farm paperwork with me as we wait for breakfast in a local bar. The olive processing will take another 2 hours. . .

This cylindrical machine which looks like an iron lung is where the oil is separated from both the fruit solids and naturally occurring water within the olives. . This used to be done with presses (hence the somewhat obsolete terms first press and cold press), but is now done by centrifugation. Old presses would literally press the oil out from between layers of paste laid out on discs (traditionally made from hemp or coconut fibre. . Nowadays, the paste is pumped into an industrial decanter where the oil will be separated. The decanter is a large capacity horizontal centrifuge rotating approximately 3,000 rpm. The high centrifugal force created allows the paste to be separated according to its different densities (solids > vegetation water > oil). Inside the decanter's rotating conical drum there is a coil that rotates more slowly, pushing the solid materials out of the system. . The water and solids at this facility come out as a pomace (seen here coming out of a pipe as a light beige liquid, SWIPE left to 2nd photo). In most cases, the oil coming out of the first centrifuge is further processed to eliminate any remaining water and solids by a second centrifuge that rotates faster. . The oil is then left in tanks where a final separation happens through gravity. .

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