[thoughtexprmnt]

Two things to look for when selecting olive oil at the supermarket - a dark glass bottle, and a harvest date printed on the label. Granted, this doesn't guarantee you're getting a high-quality, non-blended EV olive oil, but without these you most assuredly are not.

[bluGill]

Don't go to a supermarket to get good olive oil in the US. There are a few small stores scattered around that sell good olive oil.

Dark glass is cheap and so cheap oil at a premium price comes in a fancy dark bottle. You are paying for the fancy bottle (which doesn't cost much more than a cheap plastic bottle of the same stuff - profit)

A harvest date is useful if you can find one, but doesn't really mean quality. If the date is more than 3 months ago it means subpar though which is something.

[deadmetheny]

This isn't strictly true - you can get good, real extra virgin olive oil at, say, Whole Foods, but it's gonna be from California. Tinted glass keeps UV light from degrading the product, similarly to why no decent beers come in clear glass.

You're completely correct about getting good imported olive oil from a supermarket though, absolutely.

[skolsuper]

Glass is opaque to UV

[Doxin]

The main thing about the dark glass bottle is that UV damages olive oil making it taste worse. If your olive oil is in a container that lets in UV you're guaranteed that the manufacturer doesn't give half a hoot about quality.

[darkpuma]

I'm a bit skeptical of claims like this. All standard transparent soda lime glass is opaque to short wavelength UV (UV-B and UV-C) but is in fact trasparent to long wavelength UV (UV-A) (transmission drops off rapidly under 350nm). However, what tinting is actually being employed in any particular bottle and how effective is it at blocking long wavelength UV? To be sure, there are some tinted glasses that are effective at blocking long wavelength UV, but can the consumer identify those by sight? Amber glass is meant to be pretty good at blocking UV, presumably UV-A since regular glass will block UV-B and UV-C, but amber glass seems to be a fairly complex formation and it's not clear to me if some formulations are more or less effective than others. Beer sold in clear glass is relatively rare, but green glass isn't particularly uncommon and from what I can tell ferric ion green glass doesn't seem to block UV-A any better than clear glass. Green glass made with didymium is often used as UV filters, but I don't think that's used in beer bottles.

I suspect tinted glass has more to do with marketing, consumer expectations (and maybe cargo cults) than UV protection.

(Also, what brand is in the habit of leaving their bottles of EVO sitting out in sunlight instead of in warehouses, in shipping containers, in stores, etc? When you avoid direct sunlight and electric arcs, the UV threat should be minimal.)

[bluGill]

True, but irrelevant. Dark glass is more likely to mean that someone is trying to get extra profit from the unsuspecting at the supermarket.

[divbyzer0]

By far the best indicator of quality I have found is the acidity level. The higher acidity oils tend to omit this detail in packaging. I aim for 0.3%.

The higher quality olive oils have been sold in 'tin-cans', but that alone does not indicate quality.