Although you’re highly unlikely to buy a fake olive oil from a reputable shop, producers may sail close to the wind when it comes to categorisation. Extra-virgin olive oil (EVOO), the kind highest in beneficial compounds including antioxidants, degrades with time, and faster if it is poorly stored.
“You might buy a bottle of extra-virgin olive oil that may have left the producer fulfilling-extra virgin criteria,” says Simon Poole, a UK National Health Service doctor and author of The Olive Oil Diet. “But may after several months on a supermarket shelf … no longer be extra-virgin.”
This is particularly possible if, as is common, the oil only just scrapes in as EVOO at the time it is purchased from producers by the big olive oil brands.
Oxidisation, caused by heat, light and exposure to air, is the chief degrader of olive oil, spoiling the flavour, raising the acidity and reducing its healthy properties as the antioxidants are consumed by oxygen.
So how can you be sure your EVOO really is extra? Here’s a guide to getting the good stuff.
What you should be looking for in EVOO
Label
Just because the label looks Italian doesn’t mean it is Italian - if you want to know where your olive oil is from then scrutinise the small print. Chances are it’s a blend from EU countries. Single origin from Greece or Turkey is excellent and may be better value than Italian.
Look for a date of pressing, and try to buy oil that’s a maximum of 15 months old from a shop with a high turnover. If the best-before date is all you have to work with, it’s likely to be 18 months after the pressing date. For the highest beneficial compound levels, look for specialist brands.
Packaging
Light speeds the oxidation of olive oil, so it’s important to pick one that is sold in a darkened glass bottle or a tin.
Colour
Colour generally indicates olive type, ripeness, and level of filtering rather than quality, so good oil can be deep green or golden yellow. Olive oil assessors use blue glass cups to taste so they aren’t influenced by the colour, as it’s said greener oils tend to be grassier and more fruity, while yellower oils tend to be spicier. However, those deep emerald oils turn yellow if exposed to light and heat - a bad sign - so a green colour can be reassuring.
Smell
This is a much more reliable marker of quality. Giovanni Quaratesi of olive oil importers Certified Origins advises pouring a little bit into a cup, covering it with your hand and letting it warm to at least room temperature. Lift your hand and sniff: “If you smell … freshly cut grass, fruit, veggies, anything that is very fresh and alive, that’s a great sign.”
Flavour
Look for flavours of ripe green fruit or grass, but also a slight irritation, a tickle at the back of the throat. Many of the beneficial compounds, says Poole, are produced by the plant “as a defence mechanism … slightly bitter and pungent to put mammals off eating them before they’re ripe”. There should be no trace of rancidity, though.
Viscosity
EVOO is thicker than most oils, and the lower the oxidation levels the higher the viscosity. However, this is hard to measure without specialist equipment. Monounsaturated fats, the chief component of olive oil, thicken at a higher temperature than polyunsaturated (the type of fat in many vegetable oils), so it’s sometimes said if a bottle of olive oil solidifies in the fridge, it is proof of good quality. But this isn’t always the case: the fatty acid content of oils varies widely and other oils (such as peanut) will also solidify when chilled.
Olive oil storage
The worst place you can keep your olive oil is in a big clear glass container by the cooker. Heat, oxygen and light degrade oil, so if you must keep some next to the hob, decant some into a small opaque bottle and store the rest in a cool cupboard.
Olive oil grading
Extra-virgin olive oil is just olive juice, unprocessed and untreated. It’s passed flavour tests, and has an acidity level of less than 0.8%, indicating very low oxidation.
Virgin olive oil has an acidity level of up to 2%, indicating higher oxidisation, and is of a lower flavour standard.
Refined olive oil is lower-quality oil that has been bleached and deodorised by heat and chemical treatment. Some natural antioxidants and vitamins are lost.
Olive-pomace oil is made by treating the olive pulp (left after the oil has been extracted) with solvents, and then refining it. Like refined olive oil, it’s generally mixed with a bit of extra-virgin olive oil for flavour, but it has lower health benefits than pure EVOO.
