After our delicious lunch we were treated to a tour to see the industrial side of olive oil production. A visit to Co-operativa Agricola San Giorgio is a must if you’re in the Lecce area, nicely finished off by perusing the produce in the farm shop.
I love industrial places. They are a feast for the senses. Factories provide excellent opportunities to practice capturing motion by using different shutter speeds and combined with the noise make a great video. Crates and crates of olives are standing out front waiting to be lifted.
The basic method is still widely used today. First the olives are ground into an olive paste using large millstones in the press for at least 30-40 minutes. This applies pressure to the paste and separates the liquid oil and solid vegetable matter left over. Then any water in the mix is separated by decantation using a centrifuge. Making sure the olives are well ground, this allows enough time for the olive drops to join to form large droplets and for the fruits’ enzymes to contribute to the oil’s aroma and taste.
After grinding, the olive paste is spread onto discs (traditionally hemp or coconut fibres) which are stacked on top of each other, then placed into the press. These days, synthetic fibres are used which are easier to maintain. Using hydraulic pressure of up to 400 atm, the discs are forced together and water is poured down the sides of the discs to increase percolation speed. After each batch , the paste must be removed from the discs, otherwise left overs will cause inconsistencies and contamination to the taste and purity of the oil.
Although they are ancient by design, grindstones break up the fruits’ pulp while barely touching the kernel and skin. This reduces the rate that oxidisation can occur. Using this extraction method, the amount of water used is minimal compared to modern methods of extraction. Less polyphenols are washed away and once the paste is exhausted, the ‘pomace’ has a low water content and makes it easier to manage. The disadvantages to this method are that the grindstones require more manual labour to maintain them and the process involves waiting periods which can expose the paste to oxygen and light. All this translates into a longer production time from harvest to pressing.
Separation at all stages is done using an industrial decanter and centrifugal force, spinning at 3000rpm.(Two or three phases of centrifuge can be used.) Using a hammer, disc, knife crusher or de-pitting machine, the paste is then malaxed for 30-60 mins. As small olive droplets gather, fruit enzymes create the oil’s aroma. Solids are removed by a slowly rotating coil in the drum which pushes the solids out of the system. Separated oil and water are then rerun through a vertical centrifuge working at 6000rpm removing any small amounts of vegetation water. The machinery using this method is more compact, oil production being continuous and requires less labour. Olive oil made using the two-phase centrifugal system contains more phenols and is more resistant to oxidisation than oils from three-phase or hydraulic press methods. However, this method uses more energy and the pomace can be wetter, so adding drying to the disposal process and because more water is used, it reduces the amount of anti-oxidants present in the product. There are some other methods but I don’t want to bore my readers too much!!!!
First Cold Press or Cold Extraction
The temperature of malaxation and extraction has a critical effect on the quality of the oil. When high temperatures are used to increase the yield of oil from the paste, it has a negative effect on the vitamin and antioxidants content. Under strict EU regulations, extraction must be done under 27 degrees centigrade (80 degrees Fahrenheit). Olive oil bottled outside of the EU is not covered by this standard and so the consumer has no idea what they are buying.
What does this mean to me, the person who dishes out the dosh?
Olive oil quality is equally dependent on the condition of the fruit itself. Oxidisation occurs immediately upon harvesting and the fruit should be pressed within 24 hours. During the period between harvesting and grinding, the olive’s enzymes are very active and degrade the oil. If you wait too long the oleic acid content goes up affecting the taste and making the oil more bitter. Exposure to light also affects this process, so keep your bottles in a dark cupboard or in a dimly lit part of the kitchen. If you buy a large can, it’s best to decant some into an air-tight vessel.
I do believe you get what you pay for when you peruse those shelves in Waitrose wondering why!