Is it safe to consume lemon oil in the quantities that would be found in fried food? Could I fry corn tortillas, for instance? Would it fry?
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21Essential oil as „the stuff that’s usually sold in 10-20 ml bottles” where a few drops in a diffuser are enough for a room? – Stephie Jan 13 '22 at 16:10
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2Correct; specifically the lemon variety. – user3210986 Jan 13 '22 at 16:13
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33Upvoting because, based on the answers, it's really good that you asked before trying this. – adam.baker Jan 14 '22 at 05:33
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6Since the answers highlight why it's dangerous (even in mL quantities), I would recommend normal frying and then a healthy coating of lemon juice/citric acid if you're wanting a strong lemon flavor. – Drake P Jan 14 '22 at 07:10
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9Essential oils are generally volatile meaning they evaporate at room temperature. Aside from fire and toxicity risks, it doesn't really make sense to fry with them. Typically a major point of frying with oil is that at it can reach temperatures much higher than the boiling point of water. – JimmyJames Jan 14 '22 at 19:03
5 Answers
It would be dangerous to attempt to fry in lemon oil
Lemon & other citrus oils are primarily (90+%) made up of Limonene, which has a "fire diamond" of 2-2-0:
Flammable
The red 2 indicates flammability:
Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur (e.g. diesel fuel, paper, sulfur and multiple finely divided suspended solids that do not require heating before ignition can occur). Flash point between 37.8 and 93.3 °C (100 and 200 °F).
Limonene has a flash point of only 50°C (122°F). Canola oil & most "frying oils", by contrast has a flash point of closer to 315°C (600°F).
Note that the "flash point" is the temperature where flames & active combustion take place. This is generally a good bit above the usual "smoke point" which is used to rank cooking oils. The flash point is the more dangerous temperature, as it equates to fire.
This limits the feasibility of doing any cooking in citrus oils, due to their flammability. The high limonene content would render lemon oil to be a fire hazard well below "frying" temperatures. If you've ever seen a flamed citrus peel used as a cocktail garnish, you would have witnessed the flammability of citrus oils.
Health risk
The blue 2 indicates a health risk:
Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury (e.g. diethyl ether, ammonium phosphate, carbon dioxide, iodine, chloroform, DEET).
As mentioned in another answer, even if flammability wasn't an issue, this could be dangerous. Contact with the skin can cause a rash ("contact dermatitis" if you're being technical about it) in certain cases.
Even if it didn't burn at such a low temperature, the quantity of limonene needed for cooking, and the direct contact with your mouth while eating would result in a potentially dangerous situation.
Small amounts are considered safe for consumption (and even used in supplements), but any significant quantity of lemon oil should not be consumed directly.

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19For others curious about the yellow 0, it's for instability-reactivity: "Normally stable, even under fire exposure conditions, and is not reactive with water (e.g. helium, N2)" – dbmag9 Jan 13 '22 at 18:52
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7Flammability is kinda the point. Essential oils are used for their smell, and they have an aroma because of their vapors, and they have vapors because they are highly volatile. Generally speaking, the more fragrant something is, the lower its boiling point. And while boiling point and flash point aren't the same, they tend to be correlated. – Acccumulation Jan 14 '22 at 22:47
Lemon essential oil is composed primarily of limonene. Limonene is a skin irritant at high concentration, so you wouldn't want to put it in your mouth. Limonene is also volatile enough to limit its use as a frying medium, and the vapor would cause severe lung irritation.
It would perhaps make more sense to add a bit of lemon oil to your frying oil, but again, it's a fairly volatile oil, so it would be better to add it after frying.

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By volatile do you mean the scientific sense, as in easily evaporated, or do you mean it's likely to burn? – GdD Jan 13 '22 at 17:08
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13In the scientific sense. I don't really know if it's likely to burn.... if you're frying with limonene that's honestly the least of your concerns. – Sneftel Jan 13 '22 at 17:09
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9@GdD For oils, those properties are fairly proportional. A volatile oil usually ignites or even explodes at lower temperatures. – Stian Jan 14 '22 at 08:08
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4Take note that the final sentence of Sneftel's answer says "lemon oil," not "lemon essential oil." They are not the same thing. – Brian Jan 14 '22 at 14:12
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3@Brian I'm pretty sure they are the same thing, at least anything labelled "pure lemon oil" will be... well, pure lemon oil (or lemon essential oil - same thing). Where you have to be careful is with lemon oil "products" like wood conditioners or other products which blend pure lemon oil with other mineral spirits or petroleum products. Those will usually have other words in their name to that effect, eg: *lemon oil conditioner*, etc. – J... Jan 14 '22 at 18:18
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@J...: That's technically true. However, products marketed as lemon essential oils may be sold at higher concentrations than those marketed as lemon oil. Also, products marketed for use in diffusers may not be food-grade. It's common for essential oils to have a "For external use only" warning whereas lemon oil intended for cooking usually instead has messaging like, a "add a few drops to your cake recipe" or "use in place of zest." – Brian Jan 14 '22 at 19:53
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3@Brian Sure, but in that case what you're looking for is **food grade** lemon oil - not that there's any particular difference between the lemon oil components in either, and that goes for anything you would cook with that may be commonly distributed in both food grade and non-food-grade varieties. Food grade is a guarantee about the impurities (or lack thereof), not the product itself. – J... Jan 14 '22 at 20:11
Essential oils are toxic in larger quantities. This is simply the first google hit. A few milliliters can seriously harm small children; there have been deaths from larger amounts given to little children by misguided parents.
An adult will not die as quickly but a few milliliters more may require a visit to a doctor or hospital.

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In addition to the idea being unhealthy and a fire hazard (both properly discussed in the other answers), there is one more consideration:
In order to fry something, the oil has to be way hotter than the boiling water temperature (e.g. 250-300 deg C) and still safely below the oil's own boiling point.
Lemon oil will boil below 170 deg C and you don't have a temperature interval usable for frying.
edit: I solved it!
The ordinary cooking practice is yet to employ the reflux condensers, but we can borrow them from an adjacent field - the organic chemistry lab practice:
(credit: https://biocyclopedia.com/index/chem_lab_methods/reflux.php)
This solves the low boiling point problem, the volatility problem, the flammability problem, the oil loss problem and the vapor toxicity problem - all at once.
The oil bath in the picture is important - a direct heating will enable some parts of the container to reach the self-ignition temperature of the lemon oil.
The internal magnetic bar will rather not be needed.
Well, the result will be still not tasty nor even safe to eat, but this is out of the scope of the question.

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5*Edit*: this comment is incorrect, see Peter's reply below. [I admire the chemists who managed to find out lemon oil's boiling point. Since it will also usually burst in flames when heated to only 50 C (as noted in other answers), the boiling point is not the practical obstacle for frying - it will never be reached anyway.] – rumtscho Jan 14 '22 at 09:50
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5@rumtscho The flash point is the point at which a liquid will burn *provided you ignite it*. For example, a liquor with 35% alcohol will only be usable for a flambee if you heat it in the spoon, while a 50% liquor will catch fire at room temperature. The point of *spontaneously* bursting in flames (as opposed to being lit) is aptly called the [*auto ignition temperature*](https://en.wikipedia.org/wiki/Autoignition_temperature) which appears to be [235° C](https://baptist.nl/uploads/bijlagen/Lemon%20Oil.pdf) for lemon oil (Canola: >400°C). – Peter - Reinstate Monica Jan 14 '22 at 12:10
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1@rumtscho My pleasure. Since you are a mod you are probably familiar with the [mandatory xkcd](https://xkcd.com/386/) but perhaps not with the timeless [quote from Beckett's *Watt*](https://onlinereadfreenovel.com/samuel-beckett/page,12,36049-watt.html): "For it is a strange thing, but apparently true, that those who speak speak rather for the pleasure of speaking against than for the pleasure of speaking with, and the reason for that is perhaps this, that in agreement the voice can not be raised perhaps quite so high as it can in disagreement." ;-) – Peter - Reinstate Monica Jan 14 '22 at 13:07
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6Frying above the flash point is rather popular, this is how the good part of the kitchen fires start. – fraxinus Jan 14 '22 at 15:52
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And 235°C/455°F is … not particularly far off from frying temperatures, IIRC. Which is the auto ignition temperature. So if you had the body of oil above 50°C/122°F, and even a bit managed to hit the auto ignition temp, the rest is basically guaranteed to be well over the flash point. And so you wouldn’t even need an open flame to make a wonderfully lemon-scented fireball. – fyrepenguin Jan 15 '22 at 12:31
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@fyrepenguin: Even worse, if the oil is approaching 235°C, that means it's a gas, probably well-mixed with oxygen ready to deflagrate or detonate, unless it's under high pressure to keep it from boiling. (An air-tight cooking apparatus for gas-phase oil would be a very different kind of "air fryer" than what I got for Christmas :P) – Peter Cordes Jan 16 '22 at 05:05
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@PeterCordes but what a lovely lemon scent it would have ….. mmmmm, lemon fireballs … – fyrepenguin Jan 16 '22 at 07:13
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Doesn't matter. The reflux condenser solves few things together - the fumes that are a health risk, the flammability and the loss of oil. You can keep the temperature near or even at the oil boiling point and still fry (rather slowly) the food. – fraxinus Jan 16 '22 at 13:26
The earlier answers have all contributed a great perspective on why its not safe nor feasible to fry anything in lemon oil itself.
Lemon oil, and most citrus oils in general, are obtained from the peel of the fruits. This is usually done in a cold-pressed manner ie. (squeezing the peel to release the oils contained in glands within the peel). The oil is highly concentrated and not suitable for direct use in cooking.
I understand that the initial premise of your question is that you are trying to find a way to infuse the flavor of lemon oil into a food item through frying that food item in the oil.
What I think might work well for your application eg. deep frying tortillas, is to use a food grade oil soluble lemon oil flavoring such as this one. You can prepare a pot of neutral oil, such as canola oil, and to that neutral oil, add however many drops of the oil flavoring to your desired strength.
Frying with this flavored oil should infuse the flavor into the tortillas pretty well. You need not be concerned about toxicity of flammability here, because the oil that is doing the cooking is the neutral [canola] oil itself. Just adding those few drops of the lemon oil flavoring would hardly alter the physical or chemical properties of the frying oil overall, due to its extremely small dosage quantity.
If you do manage to give this a go, I would be curious to hear results!

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Have you actually tried this? I would expect that the high heat combined with the relative volatility of the compounds which impart flavour would leave you with no flavor. – Xander Henderson Feb 02 '22 at 18:21