Essential Olive Oil Facts - Part 1. What is olive oil?

More people are getting to know about and enjoy olive oil. But there is still a lot of uncertainty. Questions I am often asked are: What to look for when buying olive oil? How to use it? Can you cook with it? Why it is better for you than some other oils?

In the next couple of blog entries I thought I would try to answer some of these questions, share some Olive Oil facts and end up with a buying guide….

What exactly is Extra Virgin Olive Oil and how is it made? How does it differ from other cooking oils?

Olive oil is actually a fresh fruit juice - the fruit being the olive picked from the trees. Although the picking can be done mechanically, in Greece I have never seen this. The mountainous terrain makes it impossible for harvesting in any other way than by hand, which is good for the olive oil!  Once picked, the olives are sorted and sifted, removing the bulk of the leaves, and then taken in sacks or crates to the olive mill, where further sifting takes place. The olives are then washed in cold water, and ideally pressed within 24 hours or less of harvesting.

By definition, extra virgin olive oil is extracted purely by mechanical means. The oil/juice is 'squeezed' from the olive by a mechanical press, under cold conditions. Hence the terms ‘cold pressing’ and ‘cold extraction’.fter washing the olives are milled and then the oil is separated from the water and the solid waste (husk and stone). Traditionally, milling was done with a millstone or hammer stone, and oil extraction iachieved by hydraulic press. A more modern method is continuous cycle centrifugation. When the olives are of sufficiently good quality, the first pressing produces extra virgin olive oil.

This mechanical method of oil extraction represents a major difference between olive oil and most other cooking oils – such as rapeseed, sunflower seed, safflower seed, coconut (the nut is the seed), and corn oil: the latter are all seed oils, not fruit oils, and cannot be extracted by mechanical means. In fact the only seed oil that can be extracted by cold mechanical pressing is sesame seed. A

This difference is important for several reasons:

  1. First, the fruit juice of the olive contains not only fat, but a water fraction which contains a number of phytochemicals which are extremely good for you.  This water element (and its contained goodness) is missing from seed oils.

  2. Second, the fact that the olive juice/oil is obtained without any heat or chemicals means that the both the fat- component and the water fraction element are not destroyed by the extraction process. In other words, the goodness is retained through the extraction process.

Most seeds however, unlike olives (or avocado – another fruit oil) don’t contain enough oil to be mechanically pressed. The extraction of their oil needs more drastic methods. There are two which are commonly used: The first is by expeller pressing, where the seeds must first be cooked to high temperatures, then crushed and finally expeller pressed; or worse still, by using a chemical solvent (yes, such as light petroleum!) to extract the oil – so called ‘dissolved oils’. So even if this is done under cold temperature, it is not the same as cold pressing! The first removes most of the goodness, and the second is positively bad for our health, as it is impossible to remove all the solvent from the oil.  It is estimated that 98% of US soya oil is solvent extracted.



    This image is taken from a research paper  describing how the protein in rapeseed is degraded during the oil extraction process. Incidentally, when you are told that rapeseed oil is also'cold pressed' the only cold pressing that it has is during the cake formation phase! The oil is still extracted with solvent.

    So even when a seed oil contains ‘good fats’ (about which more in another blog), they are missing all the extra goodness contained in the water fraction of a fruit oil – such as olive oil (or avocado oil – also a fruit oil which shares many benefits with olive oil). And second, the process of extracting the oil may actually leave harmful residues in the oil. So, all of the common vegetable cooking oils – sunflower seed, rape seed (canola seed), coconut oil (which should be avoided at all costs due to its very high saturated fat content), safflower seed oil – are seed oils which have had to be either heated or solvent treated to extract the oil. Furthermore, many seed oils are then refined, to remove any ‘impurities’ (which often includes a lot of the goodness!). All in all: NOT GOOD!

    Avocado oil and sesame seed oil are the only other cooking oils which can be mechanically cold pressed and so retain their original health value.

    What are the different grades of Olive Oil?

    Depending on the quality of the fruit and how the oil is extracted, there are several 'grades' of olive oil. The EU has classified different types according to how the oil is made and processed, its taste, aroma and texture (these are known as ‘organoleptic factors’) as well as certain laboratory measures such as acidity. 

    1. VIRGIN OLIVE OIL is produced by mechanical pressing at low temperatures which minimise deterioration in the oil. The olives are not exposed to any other process other than cleaning, centrifugation and filtration. Virgin olive oil is then subdivided into the following categories:

    a. Extra virgin olive oil (EVOO): 

    This is the first pressed pure 'juice' - and is more healthy, tastes better and lasts longer than other kinds of olive oil. In order to qualify as extra virgin olive, it must fulfil certain very strict laboratory and organoleptic criteria: 
    i. the acidity - i.e. free fatty acids (expressed as oleic acid) - must be <1g/100g (i.e. <1%); (But the best EVOOS have acidity of less than 0.5%)
    ii. peroxide <20 and waxes of <250mg/100mg.
    iii. on organoleptic testing there must be no defects (eg. it must not taste rancid or fusty) and it must have key positive qualities such as aroma, fruity taste, bitterness and pepper.

    The less good virgin olive oils are bascically ranked according to their acidity and organoleptic features as follows:

    b. Virgin olive oil – has an acidity of 1-2% and must have <2.5 organoleptic defects
    c. Curante virgin olive oil acidity  2-3.3% (curante = medicinal, i.e. for external use, not for eating)
    d. Lampante virgin olive oil has an acidity of >3.3 and organoleptic defects of >6. (lampante – used for lamps!)

    2. REFINED OLIVE OIL sounds special but in fact it is a low level oil, produced from poor quality virgin olive oil in refineries; its method of processing means it has had much of the goodness taken out of it. However, its acidity is nevertheless <0.5% - and this is often  a misleading factor if you only look at acidity values!

    3. 'OLIVE OIL' is a product made from mixing refined olive oil with virgin olive oil and has an acidity of <1.5%. In his book "Olives - the life and lore of a noble fruit",p 123) Mort Rosenblum describes how one Turkish refinery technician explained to him how

    'the worst sort of inedible olive oil (is converted) into "pure olive oil" - using activated earth filters, scalding steam and chemicals to remove nasty odors and murky colours. Caustic soda can cut the acidity from 5 or 6 percent to below 1%. ...the same level as extra-virgin oil...except that there is no taste, no colour, no body, nothing. A splash of better oil makes it saleable if not desirable". SO BEWARE!


    a. Crude pomace oil is extracted with an organic solvent and not fit for human consumption; neither is refined pomace oil. 

    b. Pomace olive oil is a mixture of refined oil from the OLIVE STONE  (i.e. comparable to a seed oil) and virgin olive oil (except lampante) and is fit for human consumption - but not advisable!

    All of the following are sold in retail food shops: extra virgin olive oil, virgin olive oil, olive oil and pomace olive oil.

    But the only type I would advise anyone to buy for consuming raw or in cooking, is extra virgin.

    Avoid anything that says ‘light’ ‘pure’ or ‘refined’!

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