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I want to try soaking wooden spoons and such (things which will come into prolonged contact with hot food) in tung oil. My local supplier says it is pure, raw and cold pressed and does not contain any chemical additives. They say it will take 3 weeks to dry, but I would not mind waiting some more, maybe months before using the kitchen utensils.

Will this get me food safe wooden utensils or does tung oil stay harmful even if fully cured? (Is it enough to let it cure for a month or so?)

Is it a good idea to add a small amount of orange oil (food safety)?

meta: Is this the wrong stack community? pro wood workers should know about the chemical properties of oil, right? :)

Higemaru
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    Didn't think I should tack this onto my Answer so adding it here. "pro wood workers should know about the chemical properties of oil, right? :)" Not so much. Same deal with most user groups (e.g. mechanics and engine oil, painters and their paints) who aren't developers or consultants to the industry. Even where a pro does happen to be a consultant they don't need to know any chemistry to be able to use the product as their respective discipline requires and report back on any pros and cons in day-to-day usage. – Graphus Nov 20 '16 at 19:41
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    For future readers of this question, note that many brands mislabel fake Tung Oil or Tung Oil blends as simply "Tung Oil". If the instructions suggest less than several weeks' curing time, you aren't using pure Tung Oil, and the answers to this question do not apply. – drs Nov 21 '16 at 10:01

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Is (pure raw cold-pressed) tung oil food-safe (for cooking utensils)?

Almost certainly yes. Just to mention, almost any oil of vegetable origin would be as well.

There's a small chance of individual sensitivity to the tung oil, as there is with so many things, but in general tung oil is not something that people react negatively to.

I want to try soaking wooden spoons and such (things which will come into prolonged contact with hot food) in tung oil.

If you are seeking to make the utensils waterproof I'm afraid you won't be happy with the results of your experiment, but I encourage you to try it anyway and see the results first hand.

No oil used in wood finishing actually provides a really good waterproof finish. Pre-polymerised tung oil may come the closest, but oil finishes of all types (using oil only, not a blended finish with resins in it) are inherently water-permeable.

Partly this is because oil doesn't penetrate that deeply into wood except into exposed end grain so there's actually very little of it left in/on the wood surface.

There is a method to greatly increase the oil uptake of wood in a reasonable timeframe, one used to produce oil-soaked wooden bearings — in short you deep fry the wood, displacing water in the wood's structure with oil. But this leaves the wood permanently oily which I don't think would be a desirable outcome here.

Is it a good idea to add a small amount of orange oil (food safety)?

I don't think there's any benefit to using that but this is something you'll have to make your own mind up about after reading up on it.

Note: there is a problem in that "orange oil" will often not be what you'd assume from the name. Obviously the expectation is that it's oil extracted from oranges but there are products with that on the label (ditto "lemon oil") which are not that at all, but instead a type of finish or wood treatment (or furniture polish!) with a citrus smell. Some of them would absolutely not be suitable for application to something intended for direct food contact.

No finish is necessary
Gotta add this FYI. Wooden utensils, just as with serving boards and most cutting boards, don't need to be finished in any way to work well in their intended roles.

A long while back it was the norm not to finish things like this and while it's still done today in some parts of the world in the West the idea has largely been forgotten about, or pushed aside in favour of one or another finish... but a great deal of this is about making things look better. While there's nothing wrong with that as a goal it tends to go hand in hand with an idea that the wood needs to be finished, but very often the treatment does nothing to improve the serviceability of a food-prep item and might even negatively affect one or more attributes.

Graphus
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  • Thank you, and yes, I will only use the real deal, for any oil. :) I have raw wooden spoons as well as a few soaked in linseed oil. I feel the oiled ones stay in better shape than the raw ones, but maybe I'm biased. – Higemaru Nov 22 '16 at 19:20
  • I've got a big jar full of cheap, unfinished wooden spoons & spatulas sitting on the kitchen counter. Occasionally, they take on a red tinge from stirring Kool-Aid or similar. Sometimes they warp in wonderful ways when left in water or over a steaming pot. Otherwise, they just... work. I don't recall ever throwing any away. – FreeMan Nov 22 '16 at 19:33
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    @Higemaru Have you tried re-sanding the un-oiled ones after the grain has been raised? After one or two rounds of this they don't go rough any more and they'll seem to hold up better. – Graphus Nov 23 '16 at 04:20
  • @FreeMan Yes it is quite amazing how long a piece of thin, unfinished wood can last when used for this sort of thing isn't it? My cutting boards are all unfinished too (some were finished when bought but never again oiled) and the oldest one I have is at least 30, still works just as well as ever. It's scrubbed clean in hot, soapy water and doesn't affect it at all. – Graphus Nov 23 '16 at 04:25
  • @Graphus No, I haven't tried that. I just bought a few raw spoons, maybe I'll just leave one raw and re-sand like you suggested. I have quite a lot to experiment with now, thanks! – Higemaru Nov 25 '16 at 10:52
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Much unlike linseed oil, tung oil is poisonous, containing terpene esters. That does however not necessarily mean that it isn't safe to use anyway.

I would surely not drink it, and you should avoid direct skin contact while it's liquid. Irritations are not uncommon, and they are not necessarily of allergic nature, but also due to the poisonous effects. Rubber gloves to the rescue.
I would probably not want a child to suck on a wooden spoon for a prolonged time either, simply because you never know.

But other than that, I believe that despite being poisonous, it is reasonably safe. The amount of toxin that you are likely to take up, even from a wooden spoon, should be very small once the oil has cured, this should be perfectly tolerable without ill effects.

Some people recommend orange oil under the conception of penetration geting better (also, terpentine is sometimes used). I am not convinced this is the case at all. However, tung oil is not entirely odorless, and orange oil may mask this, so there is a little value in doing that.
However, do note that adding orange oil means adding a common allergen, which again works against "safety".

Damon
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    Bit alarmist Damon since terpenes naturally occur in many foods. Small amounts of toxic compounds in something do not inherently make something toxic, as a phrase in English covers, "The dose makes the poison". – Graphus Nov 21 '16 at 20:01
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    @Graphus: You probably meant to either say a phrase in Latin, or German since von Hohenheim was a Swiss-German, and he wrote his works in vulgar Latin. That aside, you are correct with your nitpicking that "terpenes" in general are found in many plants and most are relatively harmless (some even exist that have beneficial effects). The particular terpenes found in the Euphorbia spp., however, are very well-known to be poisonous. If you read carefully, though, you'll note that I said although it's poisonous, I believe it is reasonably safe for "normal use". – Damon Nov 22 '16 at 07:54
  • I realise your commentary was balanced out by the rest of the Answer, hence me saying "a bit" and not suggesting an edit. Re. the issue of outright poisonous or toxic compounds not automatically making something they're in toxic because of dosage, worth noting the issue of apple seeds which contain an unquestionably deadly compound but are safe to eat (in moderation). – Graphus Nov 22 '16 at 08:03
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    Another useful answer, thanks! I don't seem to be very susceptible to negative effects from linseed, orange, tung, or poppy seed oil, but using it on kitchen utensils warrants some extra caution. – Higemaru Nov 22 '16 at 19:25