Green is good, but so is gold: The colour of extra virgin olive oil
admin | June 1, 2010The colour of EVOO ranges from dark brooding green through to bright golden yellow. While there is a common perception that green oils must fresher, this is not necessarily the case. Yellow oils can equally be as fresh and vibrant.
What Determines the Colour of an EVOO?
The colour of an olive oil depends primarily on the ripeness of the olive when picked and also on the olive cultivar/variety. Some varieties such as Verdale, Koroneiki and Bouquettier are commonly (but not always) pretty green regardless of the ripeness of the olive when harvested. However, most varieties can produce a variety of oil colours depending on olive ripeness. Not surprisingly, greener early harvest olives generally produce greener oils, while riper olives will generally produce more golden coloured oils.
The Pigments in EVOO
The colour of EVOO is primarily due to two natural types of pigments – the green coloured chlorophylls and the yellow coloured carotenoids. In fact, two types of chlorophyll are found in olives. ‘Imaginatively’ called ‘a’ and ‘b’ by the chemists, the former is bluish green while the latter yellowish green in colour. There are other pigments too, most notably the pheophtyins which are coloured brown to olive green. The immense range of colours that you can find in EVOO depends on the relative proportions of these pigments contained within the oil. Imagine a paint palette where you have a few shades of green, a few yellows and the odd duller shade. Start mixing the paints in the various proportions and you’ll be able to create millions of subtly different colours. But you won’t be able to create a blue or red no matter how hard you try! So just in case if you ever wondered why EVOO’s were never red or blue – you have your answer.
So is green good? Depends.
Green oils contain a lot of chlorophyll. Chemically speaking, chlorophyll is a bit of a strange creature. When kept in the dark it acts like an antioxidant protecting the oil from oxidation. On the other hand, it becomes a strong pro-oxidant when exposed to light, setting off a devastating chain reaction that destroys EVOO aroma and flavour, and finally results in tired rancid oil. So it’s a bit like an anti-vampire in a way. The form of oxidation triggered by chlorophyll is known as photo-oxidation and it is probably the fastest and most destructive type of oxidation that can befall an EVOO.
The carotenoids are more than just yellow coloured pigments. Actually you’ve seen them before – lots of times. The yellow colour in carrots, egg yolks and fruits like cantaloupe melons, mangoes and apricots (to name only a few) are all due to their carotene content. Our bodies convert carotene into Vitamiin A and it can also be absorbed into our fat (er, that’s why human fat is a bit yellowish by the way). Carotene is also a good antioxidant – soaking up the supercharged forms of oxygen called singlet oxygen that attack EVOO (and us).
Sunburnt EVOO
You may have noticed that if you overheat olive oil its colour dullens and it eventually becomes an unattractive brownish colour. These changes are due to the formation of another set of brownish grey coloured pigmnets called pyropheophytins. Recently German scientists have used the pyropheophytin content of suspect EVOO’s to detect ‘heating events’ – a nice way of saying detected adulteration with refined and pomace which by definition are heated at one point or other of the their manufacture, or when significant quantities of old oil that has been warmed at some point during storage have been added.
Making EVOO Green
While green coloured EVOO’s are usually that way because they have been made from early harvest aka green coloured olives, there are more or less unscrupulous ways of getting that desirable green colour into an EVOO.
Firstly the legal ways.
A small amount of chlorophyll rich leaf material will always be inadvertently mixed in with the olives when olives are harvested. Most of the time, the majority of the leaves are blown off the olives with a leaf blower prior to the olives being crushed. However, it is not uncommon (particularly in some parts of Italy) for a high proportion of olive leaves (up to 20kg/tonne) to be processed together with the olives. The result – a very green oil that is often also very bitter. Why bitter? Just pick an olive leaf off a tree and taste it. You’ll see why.
Dipping olives into hot water (60C) for a minute or so prior to processing also causes chlorophyll to be extracted, with increased greenness the result. However, hot dipping also reduces the healthful polyphenols in the oil. This might not always be a negative result if a slight reduction in the bitterness of the oil is what the producer is looking for.
Lastly the totally illegal way. The addition of an artificial chlorophyll derivative called E141i has been used by the unscrupulous to ‘green up’ seed oils like canola and sunflower to make them look like EVOO. E141i is almost identical to natural chlorophyll, but it differs in a fundamental way. Chlorophyll has a single atom of an element called Magnesium at its core. This element makes chlorophyll pretty unstable (hence green oils tend to lose their greenness with age). E141i on the other hand has a Copper atom at its core. This makes E141i more chemically stable than its natural counterpart. So much so that any oil that has been illegally coloured with E141i will stay green for years, and no amount of heating will budge it! However, thankfully detecting Copper in EVOO (the tell tale sign of E141i) is relatively straightforward and as such can be used to nail the fraudsters.
Back to real EVOO. So why do olive oil tasters use blue tasting glasses to cover up the beautiful colours of EVOO which consumers so admire? Don’t ask me. The ‘official’ justifications don’t make any sense at all – well at least not to me. But that’s for another blog.
That’s the one major problem with the organic green movement when it comes to food and that’s there really is no regulation or policing of whether or not food is “authentic” or not.
Yes, you can detect copper in EVOO, but if this was an effective detection system that was applied, no one would add artificial chlorophyl in the first place.
I would say that selecting more brown colored oil would be more health beneficial from more ripened material that has naturally had the chlorophyll removed along with the negative impacts it can have.
Does “it becomes a strong pro-oxidant when exposed to light, setting off a devastating chain reaction that destroys EVOO aroma and flavour, and finally results in tired rancid oil” mean I should store green olive oil (or any olive oil) in a dark place to preserve it longer?
Also, does storage temperature matter?
Yes and yes. I’d also recommend puting it in the fridge if you just take it out and use it occasionally.
If it were applied is the key. The test is very effective as high levels of copper in an olive oil mean only one thing. That it has had artificial colouring added to it. Not sure about your last point. Gold coloured oils are full of carotenes which is good, but chlorophll never hurt anyone – just ask Popeye!