As with so many things we eat or drink, the quality of olive oil depends on many factors: the quality of the starting ingredients, the knowledge and skill of the producers and manufacturers, the care taken in processing and storage.
Of course there are both laboratory and organoleptic (aroma and taste) 'measures' of the quality of olive oil, but there is also the very important subjective element of personal Taste, with a capital T - which differs not only from culture to culture, but from person to person.
The best olive oils are, by definition, extra virgin. Pre-requisites for any good quality olive oil are how and where the olives are grown (horticultural techniques - geography, altitude, microclimate, cultivation) picked and processed.
It may seem obvious, but it is surprising how often key essential guidelines are not followed, and how often commercially available olive oils (even in some famous stores) fail to make the grade when tasted by professional olive oil tasters.
the trees and olives from which the oil is made must be HEALTHY (no fly or other infestations or disease)
the olives must be FRESHLY PICKED, stored carefully until pressing and PRESSED WITHIN A FEW HOURS OF PICKING; this minimises fermentation or disease (eg mould), affecting any olives that might have been damaged during picking;
conditions in the olive factory for processing and pressing the olives must be super-clean and well maintained;
the correct temperature must be maintained throughout at every stage;
the olives should be exposed to minimal amounts of air during processing;
the resulting olive oil must then undergo laboratory and organoleptic (taste and aroma) testing to ensure that it is indeed 'extra virgin olive oil'.
Finally the resulting oil should then be stored in nitrogen steel containers until bottling
After those pre-requisites, certain other variables go towards make a really good olive oil. According to Paul Vossen, an olive oil expert at the university of California, the two most important determinants of quality and of taste are olive variety and maturity.
The olive tree is indigenous to the mediterranean (in fact some define the Mediterranean region as where the natural growth of the olive tree starts and ends) but is now grown in many parts of the world including the 'new world' - eg Australia and California - where farming is intensive. But for all olive varieties their most naturally suited habitat is the Mediterranean basin. This, together with the hundreds of years worth of experience in cultivating olives that exists in the mediterranean agricultural population, explains why olive oils from this region tend to be better than elsewhere.
There are around 1500 different cultivars (varieties) of olive - far more than the number of grape varieties - and a corresponding variety of styles in olive oil. The huge variety of oils available is still unexplored and those available commercially are just the tip of the iceberg! But olive oil experts agree that the small fruits like the Greek koroneiki make the best oil, but they are difficult and expensive to cultivate and currently the market place is dominated by the easier to grow (and higher volume yield) Italian and Spanish varieties. Some of the best commercially available olive oils are made from these olive varieties (in alphabetical order!): Arbequina, Coratina, Cornicabra, Koroneiki, Moraiolo, Picual. These generally make excellent oils and are long-lasting, and provided the oils is made well, will contain high levels of polyphenols.
Choosing the right time to pick the olives is hugely important. Oil content increases as the olive ripens from green to black, often giving a fruitier, sweeter flavour to the oil, but conversely, the 'health' components - the phenols and aromatic subtstances which give oil much of its quality and pungent or bitter elements - are highest in younger green olives, declining as the fruit ripens.
Harvesting olives with an eye to the taste and quality of the final olive oil takes skill and experience. Oil made from predominantly darker, riper fruits tends to be softer in taste, more subtle, less pungent, but generally does not last as long and has less health value. This video shows some very ripe little Black beauties (Koroneiki olives ripe for picking) oozing with olive oil. These olives may be small (as is typical for koroneiki olives) but they are packed with oil. Sometimes the oil actually oozes out of the surface in droplets.
Oils made predominantly with greener younger olives will be more pungent, bitter, peppery and extremely heatlhy with low acidity, but not so easy on the untrained palate; however, they have a very long shelf life. A perfect combination of greener and darker olives, with the vast majority just turning from green to black, with a spattering of leaves in the mix, results in rich green-gold aromatic olive oil, strongly accented flavour, distinct bitterness and pepperiness with unique indivdiual notes depending on the cultivar and microclimate. Olives picked on either side of this optimum 'window' produce a marked difference in quality of the oil.
So what you go for within this range of quality combinations depends on 'Taste' and what you hope to get out of an oil. As with wine, there is a huge range of olive oil tastes, and if you are lucky, occasionally olive oil labels give a helpful description. There are rich pungent oils, subtle and mellow, sweet and creamy. Some are better as dips or dressings, other for different types of cooked dish or even sweet desserts. But certain features are always signs of quality: aroma, fruitiness, grassiness, pepperiness, bitterness and pungency.
What to look for when buying an olive oil (and what to avoid)
Unfortunately most commercially available olive oils in the EU provide a bare minimum of information - no more than that required by EU regulations - which is not much.
- Make sure it's extra virgin! The starting point, at the very least, is to make sure the olive oil is 'extra virgin'. Many people ask me if the (extra virgin) oil is also 'cold pressed'. The answer is, by definition, yes: an olive oil can only be legitimately called extra virgin if it has been both cold pressed and cold extracted.
- Provenance: where has the oil has come from? Greek olive oil is universally good, producing more extra virgin olive oil as a percentage of production than any other country in the world (incidentally Greeks also consume more extra virgin olive oil per capita than any one else!). Cretan olive oil in particular is renowned for its quality, with around 98% being of high extra virgin quality (i.e. very low acidity). Portuguese olive oils, many Italian oils and Spanish oils are also very good. But bear in mind that country of origin does not always mean what it says: EU regulations state that an oil can be the 'product' of a single country provided at least (only) 50% of the oil originates there. The rest could come from......? Look out for olive oils which come from 'Private estate' or have 'PDO'/'PGI' certification (the equivalent of appellation controllee) - these are nearly always signs of high quality and safe provenance.
- Acidity: The acidity of olive oil is a measure of the (unwanted) breakdown of fat (oil) into its free acid components - and the higher the acidity, the less good the oil. By definition extra virgin olive oils must have an acidity of less than 1%; but this is not a very stringent test: there is a world of difference between an olive oil with an acidity of, say 0.95%, and one of 0.2%. In other words, the category of extra virgin olive oil comprises a potentially very mixed bag. The best olive oils, and the only ones that we would ever consider selling at Liquid Gold, have an acidity of 0.4% or lower. Most olive oil bottle labels do not show the acidity (I wonder why?). But look for it when buying an oil, and you may strike lucky! Those that have a low acidity are the ones that are likely to want to show it!
Take home message: the lower the acidity, the better the olive oil.
- Date of harvest: Ideally olive oils should show the date of harvest, but few do. Aim to buy oil from the most recent year's harvest. Older olive oils, providied they are extra virgin, are perfectly OK and never actually 'go off' (which is why tolive oils display a 'best before' rather than 'use by' date. But older olive oils tend to lose their aroma and some of their antioxidant properties.
- Olive variety: Look out for arbequina, coratina, cornicabra, ,koroneiki, moraeiolo, picual.
- Long shelf life (18 months-2 years) good olive oils will have a long shelf life. In fact most extra virgin olive oils will last for years (if you should wish to keep them that long!) provided they are kept in a dark cool place, in a closed container.
- Choose dark bottles or tins and an air-tight top - reduces oxidation so the oil is better preserved
- Filtered or unfiltered - filtered olive oil contains less of the fruit debris, and thus tend to last longer, but may taste less fruity as a result; however, on the whole, unless you are planning to use the oil within a couple of weeks, it is best to go for a filtered oil.
- Colour: people often think that theh colour of the oil is very important to quality. The colour depends on the amount of chlorpophyll (the green pigment from the leaves) and other pigments (eg yellow from vitamin K) in the final oil, which in turn depends on the proportion of green:black olives in the mix, on the number of leaves (often deliberately left in during the curshing process to add pungency flavour) and on whether the oil has been filtered or not; don't let colour influence you unduly; there is little correlation with quality.
WHAT TO AVOID:
- AVOID any olive oil described as 'light' or 'refined' - these are oils which have had much of the pungent aqueous fraction (which contains the aroma, antioxidants and vitamins) extracted and taste bland.
- AVOID 'BLENDED' OILS unless the bottle clearly states the exact proportions of the olive variety blend and country of origin
- AVOID OLIVE OILS WHICH ARE HEAVILY STUFFED eg with peppers, garlic or other ingredients as the additives are often used to boscure the taste of poor quality oil.