> Fluorescence spectra of some common vegetable oils, including olive oil, olive residue oil, refined olive oil, corn oil, soybean oil, sunflower oil, and cotton oil, were examined in their natural state, with a wavelength of 360 nm used as excitation radiation. All oils studied, except extra virgin olive oil, exhibited a strong fluorescence band at 430–450 nm. Extra virgin olive oil gave a different by interesting fluorescence spectrum, composed of 3 bands: one low intensity doublet at 440 and 455 nm, one strong at 525 nm, and one of medium intensity at 681 nm. The band at 681 nm was identified as the chlorophyll band. The band at 525 nm was at least partly derived from vitamin E. The low intensity doublet at 440 and 455 nm correlated with the absorption intensity at 232 and 270 nm of olive oil. The measurements of these fluorescence spectra were quick (about 5 min) and easy and could possibly be used for authentification of virgin olive oil.
From a Halloween website, may provide a clue to the red.
> Chlorophyll is green under regular light, but will fluoresce red under a black light. Chlorophyll fluoresces red under UV light.
Getting way off topic, but if you hit ordinary peanut butter with strong light, it glows afterwards. Go into a very dark room, adjust your eyes to the dark, look away with your eyes closed/covered as you hit a jar of peanut butter with a camera flash (not the household item it once was, sadly), and then look at the peanut butter. It's glowing!
I heard this on the Internet and didn't believe it, but tried it for myself, and yup. It glows.
There's a yellow mica pigment that when used in soap making it turns a very reddish-orange (almost like rust) until the saponification has completed and then returns to yellow. It is very disheartening the first time you see it and start to think how your batch of soap is going to not be what you hoped, and then 24 hours later it looks exactly how you hoped.
That would be my guess as well. After thinking about this further, I do remember as a kid using the kits for dying eggs for easter (somewhat belated topic) that required vinegar instead of water. The yellow dye would also appear orange until it dried as yellow. So, yeah, I'm leaning towards the pH as to the cause, but we still don't know the reason. I'm going to deliberately NOT go down that rabbit hole...*
"An acid-base indicator is an organic compound that changes color with a change in pH. Methyl orange is a very common acid-base indicator, red in solutions that have pH values less than 3.2 and yellow in solutions with pH greater than 4.4. Indicators change color because the chromophoric system is changed by an acid base reaction (see below)."
https://chem.libretexts.org/Ancillary_Materials/Laboratory_E...
* I swear I tried really hard. Luckily, the hole wasn't too deep
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.
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.
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 ;-)
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.
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.
I believe most use a synthetic version. I’ve only had the natural one a few times and it was quite different, but the drink wasn’t as sweetened so that might have been the difference.
- the label of every bottle of EVOO uses short country codes to indicate where the oil came from, which is often multiple countries. this doesn't mean it's worse, but there are more ways some part of it could have not been great.
- extra virgin olive oil is a juice that will go rancid from excessive light, oxygen, or temperature fluctuation. it's basically like red wine. once you open the bottle, use it quickly, and keep it in a dark dry place. make sure the bottle is glass and is darkened.
- high phenolic olive oil is more expensive to produce (and thus buy) but contains more polyphenols.
- more olive oils now carry seals of authenticity. find one, Google it, see if it looks legit. there are many different certifications. Italy was the country with the most EVOO fraud, so be more circumspect with oil from there.
Be very careful when infusing your own oil. Botulism is a real concern, it is often necessary to soak your aromatics in a citric acid solution before infusing.
A recall a number of news items from a few years ago which talked about how some olive oil vendors were adulterating their products with other oils. If this phenomenon could be better understood maybe there would be a rapid, optical/spectroscopic way to characterize olive oil purity.
The simpler, cheaper, and faster you make the test... the more quickly it will be defeated by the adulterators. Much like spam filters and SEO, leaking anything about how you defend against an attack just makes the attackers marginally improve their game.
Simple amine/nitrogen tests for protein is how we got poisonous melamine in fake milk and wheat gluten killing babies, dogs, and cats.
That’s not entirely true. The domain within which the cheating can occur shrinks by eg checking certain properties, tho the problem you’re talking about happens when only a few properties are checked because then of course only those properties need to be gamed/manipulated. It’s about how much coverage your tests have over the properties of what you’re testing
You test at least moderately close to the actual target and you punish those who are breaking the rules brutally (it is actually food safety!). Instead we allow Olive oil that isn't and Fish that aren't because, nobody has died yet? Allergies are possible even at very low levels.
My real point wasn't the simplicity or cheapness, but often the biproduct of those is that it's a test you already have that doesn't measure what you want (nitrogen rather than protein). In the case of Olive oil, if what we cared about was it's fluoresced color rather than the material in it, that would be great.
If what we care about is components, random GC/IR spectroscopy (perhaps after centrifuging) to see the actual compounds with consequences would be a better choice than the cheapest thing they can just add another weird chemical to defeat.
A funny version of this is Manuka honey. It's not easy to define and it's slowly turned into an NZ versus Australia thing. There have been examples where bees that only gave Manuka to feed on are making honey that doesn't meet the standard, and bees that weren't thought to be feeding on Manuka have been making Manuka honey.
I have seen recipes for making non compliant honey into compliant honey (to be clear, the input honey is Manuka, but the lab test wasn't being being passed). It's about blending various types of honey.
It's a bit dumb in my view and needs a better test. As you say, it's meeting the test, not the objective of the test.
Yes, if only. I continually hear that much olive is not what it is supposed to be and it seems that authorities empowered to do something about this don't do much to stop it or perhaps they're fighting an uphill battle. In general the higher the price, the more likely the product is 100% genuine. The logic here might be that there's not that much profit in adulterating pricey oil selling rather limited quantities.
It'd be nice to see some real testing and verification. I've resorted to buying only California olive oil because I have more trust in the regulation of domestic products than I do in the regulation of imports.
It's interesting to note that California Olive Ranch's 100% domestic olive oil costs quite a bit more than their 'world blend.' I'm guessing that world blend includes imported not-really-olive-oil.
I don't know about "garbage". What do you mean by "garbage"? Do you mean not from olives? Not extra-virgin? Or just not very nice? Where? Perhaps this is true in the USA? I'm in Europe, and I don't know anything about the US olive oil market.
I do believe that a lot of EVOO isn't what it purports to be; for example, I believe a lot of purportedly Italian EVOO is cut with Spanish oil; but I can't substantiate that belief.
Its bad enough out there that the general public thinks the smell of hexane is what olive oil is supposed to smell like. Like you open a container of hexane in the chemistry lab and people say it smells like cooking oil. Um... not supposed to, no.
Kind of like how younger people think tomatoes and strawberries are supposed to be flavorless and odorless.
What surprised me was finding out that US people think that EVOO burns easily and turns bitter when fried. I found out when I was watching a youtube video from a foodie influencer, I'll see if I can find it.
Anyway, for me that's incomprehensible. I have stir fried with EVOO all my life and I have never seen it burn. The only exception is when I've accidentally, and stupidly, left the pan with only olive oil in it in full heat and went off to do something else, at which point it starts smoking and smelling bad. I have also never had it turn bitter, no matter what I've done with it. I've burned food cooked in olive oil, and occasionally the food has turned bitter (burned onions and garlic taste bitter for example; eugh) but mostly it just tastes burnt.
I've also used olive oil for deep frying and again it has never burnt on me, although lately I prefer to use cheaper oils, like sunflower oil, also because I find that deep frying with olive oil makes food taste too heavy, as if you cooked it in lard or fat (and that's not what I'm going for when I make chips or falafel, say).
So my conclusion is that people outside the Mediterranean, including in the US, just don't normally cook with good quality EVOO. I can certainly see lower quality olive oils behaving badly at high temperatures.
Extra virgin olive oil is definitely on the lower end of cooking oil smoke point spectrum, that is not really contentious point. Refined olive oils (e.g. extra light) tend have higher smoke points, same is true afaik for most vegetable oils.
If you have not observed olive oil smoking, then that is more reflective of your cooking habits than the oil itself.
Are you sure about that? Because my cooking habits are not anything strange. As I say above, I stir fry and I've deep fried, and I do everything else that you can do with shortening, with EVOO, and it doesn't burn.
Where does your information about EVOO being "on the lower end of cooking oil smoke point spectrum" come from?
And what kind of EVOO are we talking about? There are different qualities of EVOO with drastically different behaviour, but they're all sold as EVOO.
The two lists you found never say what "Extra virgin olive oil" they list, where it came from, and how they knew it was not adulterated. They don't say where the numbers in their tables originally come from, either (they list secondary sources, like food textbooks and wikipedia) [1].
Surely you can see that if "EVOO" is commonly adulterated with lower-quality olive oils, then the measurements of its smoke point are not going to be representative?
>> If you disagree then the burden of proof is on you.
I'm sorry but why is there a "burden of proof" on anyone here? I just remarked that I've never seen olive oil burn while cooking. How exactly could I "prove" that?
I hope you are not trying to invite yourself over for dinner :|
_______________
[1] What's more, the second source seems really confused about the difference between extra-virgin and refined olive oils:
You will note that refining oils tends to increase the smoke point as impurities and free fatty acids are removed. Hence refined ‘extra light’ olive oil has a higher smoke point than extra virgin olive oil. The table shows that high quality extra virgin olive oil has a higher smoke point than refined – due to the presence of anti-oxidants and low free fatty acid levels. Another selling point for high quality extra virgin olive oils.
So which one is it? Is it "refined 'extra light' olive oil [has] a higher smoke point than extra virgin olive oil" or is it "high quality extra virgin olive oil has a higher smoke point than refined"?
Thanks for those links; I didn't realize that clarified butter came in with such a high smoke point.
I usually use a mixture of (unclarified) butter and EVOO for frying steaks; tonight I shall try just clarified butter (with flavourings - thyme and garlic). It makes sense; and maybe I'll get a decent pan-sauce this time.
The only exception is when I've accidentally, and stupidly, left the pan with only olive oil in it in full heat and went off to do something else, at which point it starts smoking and smelling bad.
Getting a little off-topic here, but as a former firefighter, please allow me to plead with everyone reading this to not ever start cooking (on the stove-top anyway) and "go off to do something else." Fires start (and spread) much more rapidly than most people's naive intuitions tell them, and we're also much more vulnerable to getting distracted and forgetting about the cooking, than most of us want to admit.
Note that cooking (particularly including unattended cooking) is generally the leading cause of structure fires, at least in the US in recent history.
Cooking was the leading cause of reported home fires and home fire injuries in 2015-2019 and the second leading cause of home fire deaths. Cooking caused 49 percent of reported home fires, 20 percent of reported home fire deaths, and 42 percent of home fire injuries.
Based on 2014-2018 annual averages:
Two-thirds of home cooking fires start with the ignition of food or other cooking materials.
Clothing is the item first ignited in less than 1% of these fires, but clothing ignitions caused 8% of the home cooking fire deaths.
Ranges or cooktops account for three-fifths of home cooking fire incidents.
Unattended equipment is a factor in one-third of reported home cooking fires and over half of the associated deaths.
Frying dominates the cooking fire problem.
Well that's me told then. I promise I won't do it again, sir :P
For the record, when I say I "went off to do something else" I don't mean I left the pot on and went away, I mean I stayed in the kitchen and turned my back to it, while I was preparing to cook. This happened last summer. I started heating some oil in my French oven to brown some meat. It takes some time to heat the oil because I start from a low heat and increase it gradually to avoid damaging the pot (enamel is very sensitive to sudden temperature changes). Because I'm an idiot, I eventually turned the heat all the way to the max, even though it's a French oven and it will get hot enough to brown meat even at medium heat. In the meantime I prepared my other ingredients, then I turned back to the pot and it was smoking, so I took it out and left it to cool down, then changed the oil and started all over again. I think this has happened a couple more times over the years, when I changed homes or got a new stove.
I have certainly managed to burn food in hot oil, of course. That makes a lot more smoke and smells a lot worse. I have never seen any flames though. And I'm completely paranoid about frying, not even deep frying. A friend of mine had an accident when we were kids, when frying some eggs, and it's left him a scar for life, so I still treat frying oil a like an extremely dangerous substance. Which it is.
Burning it is easy, and a technique sometimes to add astringency for balance depending on what exactly you’re doing. Common mistake is to heat oil on a cold pan though - lots of unnecessary burning of flavor/smoke to reach sometimes necessary high momentary temperatures
I’d have to find the video, but some outfit did a survey of all the various “extra-virgin olive oil” brands on US store shelves, and found that most (not “some” -most-) were crap.
I think the issue was most were more like “pure” olive oil, with food coloring.
Many of the pricey ones that come in small, expensive bottles, were not actually what any decent European would expect from the cheapest canned oil.
The biggest issue is people using stale oils from over a year ago instead of fresh harvest. Olive oil loses flavor and goes bad earlier than it goes completely rancid. Most retail is deceptive about harvest date.
A lot of Italian olive oil isnt from olives. There was a huge scandal a few years ago of local producers adulterating olive oil (right around the time the dioxin laced mozzarella happened)
Thats why I buy Californian or Greek olive oil. Not that I trust Greeks more than any other European, but their very good stuff is so good its obviously olive oil.
Some excerpts from the article (cherry-picked to be relevant to the conversation):
>> There have been allegations, particularly in Italy and Spain, that regulation can be sometimes lax and corrupt.[75] Major shippers are claimed to routinely adulterate olive oil so that only about 40% of olive oil sold as "extra virgin" in Italy actually meets the specification.[76]
>> On 3 January 2016 Bill Whitaker presented a program on CBS News including interviews with Mueller and with Italian authorities.[85][86] It was reported that in the previous month 5,000 tons of adulterated olive oil had been sold in Italy, and that organised crime was heavily involved—the term "Agrimafia" was used. The point was made by Mueller that the profit margin on adulterated olive oil was three times that on the illegal narcotic drug cocaine. He said that over 50% of olive oil sold in Italy was adulterated, as was 75–80% of that sold in the US. Whitaker reported that three samples of "extra virgin olive oil" had been bought in a US supermarket and tested; two of the three samples did not meet the required standard, and one of them—with a top-selling US brand—was exceptionally poor.
>> A Carabinieri investigator interviewed on the program said that "olive oil fraud has gone on for the better part of four millennia" but today, it's particularly "easy for the bad guys to either introduce adulterated olive oils or mix in lower quality olive oils with extra-virgin olive oil".[88] Weeks later, a report by Forbes stated that "it's reliably reported that 80% of the Italian olive oil on the market is fraudulent" and that "a massive olive oil scandal is being uncovered in Southern Italy (Puglia, Umbria and Campania)".[89]
I'm from Greece; you know, the other major oil producing country :P We, too, like the Italians and the Spanish, value olive oil very highly. I don't know of any adulteration scandals for Greek EVOO, but that doesn't mean it doesn't happen. It's easy to believe that a producer whose oil turns out not very good in a particular year, even if it is normally good-quality would feel rather desperate and it's easy to see how some would be tempted to do something about it. For example, a few years ago in Corfu, there was much anger when much of the olive oil produced on the island were found to be unfit for human consumption because of very high levels of pesticides. That year, the communally organised spraying of olive groves from the air was stopped and produces had started spraying their olives on their own. Apparently many just overdid it, presumably following the age-old wisdom that if a little is good, a lot is better. Even without that little mishap, olive oil from Corfu is normally too acidic, because of the way the olives are collected (they are left to fully ripen on the trees and collected when they fall off naturally). That means that even extra virgin olive oil produced in Corfu may not be the best quality. That in turn means it won't be bought at the same price as better quality oils by the large bottling corporations. So it might well end up sold to the Italians and blended with their own oils, of whatever category. In that case, the consumer may buy "Italian" and "extra virgin olive oil" but even if it is really EVOO, it might still be not the best quality; but it will be sold at a high price anyway.
I have to confess I can't be sure I haven't inadvertently bought second-quality, or even adulterated, EVOO at some point in my life. I consume vast quantities of the stuff. I only cook my food with it, basically, rarely anything else. I am pretty sure I could identify non-EVOO with eyes closed. A couple of weeks ago my partner bought some olive oil and when I went to cook with it, it looked... different? Kind of too thin and too clear. I checked the container and it was blended oil that included refined oils. The container was exactly the same as the one of the EVOO we normally buy so my partner mistook it for our standard. But it was obvious it wasn't our standard. There's a clear difference. On the other hand, I'm not sure that the people who adulterate EVOO make it so easy to tell.
> Fluorescence spectra of some common vegetable oils, including olive oil, olive residue oil, refined olive oil, corn oil, soybean oil, sunflower oil, and cotton oil, were examined in their natural state, with a wavelength of 360 nm used as excitation radiation. All oils studied, except extra virgin olive oil, exhibited a strong fluorescence band at 430–450 nm. Extra virgin olive oil gave a different by interesting fluorescence spectrum, composed of 3 bands: one low intensity doublet at 440 and 455 nm, one strong at 525 nm, and one of medium intensity at 681 nm. The band at 681 nm was identified as the chlorophyll band. The band at 525 nm was at least partly derived from vitamin E. The low intensity doublet at 440 and 455 nm correlated with the absorption intensity at 232 and 270 nm of olive oil. The measurements of these fluorescence spectra were quick (about 5 min) and easy and could possibly be used for authentification of virgin olive oil.
From a Halloween website, may provide a clue to the red.
> Chlorophyll is green under regular light, but will fluoresce red under a black light. Chlorophyll fluoresces red under UV light.