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Comment by robert_tweed | Hacker News Reader

I don't have a green laser, but I just tried shining a 365nm UV torch on the various bottles of oil in my kitchen.

My good EV olive oil in a glass bottle goes a sort of pinkish colour. With the natural colour of the oil & the way the glass reflects/refracts light, it makes it look like copper.

I don't get the same effect with cheapo refined olive oil in a plastic bottle. I get a bit of fluorescence - the normal violet colour and much less than say a white piece of paper - but all or most of that is just from the container.

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Make sense. Plastics are notorious for absorbing in the UV range- for most useful spectroscopy experiments below ~400 nm we have to go straight to quartz cuvettes.

Recommended video if you want to dive deeper into UV absorption: https://www.youtube.com/watch?v=vwsHRrDYu5o

What happens if you put some of the cheap oil in a different container and then shine it with the torch?

This is science. Do it first before you bring the torch to the supermarket ;)

Hey. I wondered about that, too! Because of the slightly green tinted bottle.

Used about 1 fluid ounce, first in a 'Schnapsglas(s)', then in 2 different plastics. In an otherwise dark room.

Still pinkish shine, but different hue. Hard to tell because the light is so BRIGHT and I didn't want to use more oil in other containers. Just what I needed for cooking anyways ATM ;-)

I just tested that with a small LED-flashlight, which has a very nasty bright white beam. Works the same way.

Nothing special, no hypersuperduper, just https://kodakbatteries.com/flashlights/focus-120/ for 4 EUR with batteries included.

On this:

https://global.filippoberio.com/products/olive-oils/extra-vi... from them

https://en.wikipedia.org/wiki/Filippo_Berio

So... reading the wikipedia-article about them and their (former?) practices, and the bottle which says mixture of olive oils from the EU, makes me wonder if this is useful at all?

Or is it just a 'good' mixture?

Edit: I mean, it's ok for my taste and sense of smell. But what does that say about the biochemical quality of the oil?

Interesting. I wonder if this technique could be used as an olive oil purity/quality test of sorts? Maybe correlating a few samples of various kinds, along with some external form of verifiable testing, it may be possible to figure it out.

I'm definitely taking my UV torch to the supermarket next time. However, most good olive oils come in dark glass bottles, so I don't think it will be possible to check those. Might be interesting to look for variation among the cheaper EV ones.

The article mentions differences between brands, but IDK if there's a specific correlation with quality other than that fake olive oils certainly won't turn red/pink.

I think your instinct is right: the dark glass is going to negate any test.

I always assumed that products like olive oil sold in thick green bottles were sensitive to degradation by (UV, sun)light, so if that is true then by definition a casual in store test is not going to work. But perhaps green bottles mean nothing vis a vis light.

I do recall that brown bottles were a thing in brewing to prevent beer from becoming funky by the action of light, but perhaps oils aren't susceptible to that.

Olive oil absolutely degrades in light. Even in dark bottles. Really high quality olive oil is sold in opaque ceramic containers.

It’s the same as beer. Light degrades the beer or oil. My olive oil research says a lot of cheap oils are already going rancid by the time you buy them. Very good quality bill oils, like Costco’s EVOO, will go rancid before you can use it all.

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