Quality in Olive Oil

If you look carefully at the array of olive oils in the supermarkets you will see that there are a number of different types and grades on sale. As soon as olive oil is produced it is graded for quality. The very best olive oil - extra virgin olive oil - is stored or bottled immediately after pressing, just as it is. However, it must undergo a range of stringent tests to check that it is up to this very high standard.

If an oil fails these tests it is sent to a refinery. The resulting refined oil has absolutely no aroma or flavour so it is mixed with a little extra virgin olive oil to give it a pleasant taste. The product is known as olive oil. Some refined olive oils have less of the more flavoursome oil added to it and in the case of Filippo Berio it is known as "Mild and Light" olive oil - this is used for frying and baking, where no discernable olive oil taste is required.

Some refined olive oils are produced not from the oil which comes out of the milling process but from the solid residues. This residue, or pomace, contains a small amount of oil which is removed with the use of solvents. The resulting oil is then refined and flavoured in the same way as ordinary olive oil. This product is known as olive pomace oil. Filippo Berio does not pack olive pomace oil.

What are the quality tests?

There are a number of chemical tests which are used to ascertain whether an oil is actually made from olives and if it is extra virgin or not. One of these tests measures the "acidity" or levels of free fatty acids in the oil. It is a good indication of how well the extraction process has been carried out. Extra virgin olive oil must have an acidity level of less than 0.8%. Ordinary olive oil and olive pomace oil must have acidity levels of less than 1.00%.

Another test, the "peroxide test", is used to check levels of oxygen in the oil. This is important because as olive oil comes into contact with the air it starts to oxidize and so to deteriorate. This test measures the degree of oxidation so far. Extra virgin oils must have a peroxide level of less than 20.

Further tests are carried out for adulteration and to double check oxidation levels. There is also an important organoleptic or taste panel test. Even if an oil has passed all the chemical tests it must also have a "perfect aroma and taste". If it does not it cannot be bottled as extra virgin oil and must go to the refinery.

In recent years some producers have printed acidity levels on their labels but under new European legislation producers who wish to show the results of tests must show the results of all of them, not just one.