Food in contact with wood

DanG · December 03, 2009, 08:42:37 PM

SD, you're sounding like somebody who just soaked all of his Christmas cutting boards in Lee Valley tung oil. :D :D

That one little statement in the IFAS link I posted is enough to keep me away from the stuff: "One seed can be fatal to a human." A seed is about the size of a pecan, and the oil from it can probably finish about one square inch of wood. Why would you take the chance?

SwampDonkey · December 03, 2009, 08:50:08 PM

No, I don't stock any. What I would use is mineral oil. It's way cheaper and about the worst that can happen from consuming it is a visit to the can. And I doubt a whole table spoonful would be on my slice of bread unless there is some shotty wood finishing going on. :D

Brad_bb · December 03, 2009, 11:25:04 PM

Beenthere, Yes, I am considering cutting the pressing plate. I've got to get more into it and determine if I really need to or not. I might have enough slop between the press plate and and the diameter of the lower cast stand to fit my basket. Haven't gotten there yet though. If I have to have it turned, I can. Stainless straps would be nice if I can get a hold of some, but steel will work. I have another press that came with a basket. I refinished it's steel bands much as I'm going to finish this press. Blast, PPG Epoxy primer (I restore classic cars too so I'm pretty good with paint and body), black paint, maybe baked to harden, and finally the food grade clear epoxy. I used stainless screws for the band to staves.
I was going to sell this press on ebay, but then thought twice and since I'm out of work, I have the time to make the basket and finish it. The other press I use has some gaps in the staves that are too large(I didn't make that one), so this is my chance to build a better basket. If it comes out better, I can sell my other press.

ljmathias · December 04, 2009, 07:24:01 AM

I think the confusion here has to do with the basic chemistry that happens when tung oil (and the other drying oils) actually "dries." Turns out to be a complete misnomer: drying involves loss of a solvent such as water or petroleum distillates (used in polyurethane coatings). As the solvent evaporates, the polymer that is dissolved in it thickens, hardens and solidifies, just doing what it naturally wants to do.

Drying oils do something totally different: their molecules chemically react with the oxygen in air to form chemical bonds with each other. This leads to polymers, or crosslinked polymers actually, that are hard, solvent resistant and non-digestible. Doesn't mean there still isn't present some of the "poison" molecules that make them dangerous, but more than likely, those are also bonded in and can't leave anymore.

Process is similar to what happens when we make polystyrene from styrene: the styrene monomer is volatile, smells bad and is bad for you, but once you make a polymer out of it, you can drink hot coffee from foamed cups made from it. Key is to let all the styrene leave or get reacted in.

One of the problems with drying oils is that they are sometimes "cheated." They may be mixtures of different kinds of cheaper oils, or worse, they may contain additives that accelerate the polymer forming reaction- cobalt is one of those and it's routinely used in linseed formulations, for example. Problem is, these additives don't get bonded into the polymer and they can leach out and be digested by us weak humans: poison. So unless you use "pure" tung oil, you don't know what you got...

Would I eat off or work on a pure tung-oil treated cutting board? Sure, I would personally. Would I sell one to someone else? Probably not. Would I give one to a relative? Probably so, if I didn't think they might sue me if they didn't cook their chicken long enough and got food poisoning. It all comes down to degrees of risk, and what is acceptable risk for you. What's acceptable for some isn't for others. While you can't be too safe (well, maybe you can- remember the latter days of Howard Hughes?), you can be too careful: as one of the signature lines of a forum member points out, "something" will kill you no matter what. It's how we pursue and enjoy life before that that's important.

I'd be much more worried about second- or third-hand smoke from cigarettes than pure tung oil on a food-contact application; but then that's me, as an ex-smoker and prostate cancer survivor...

Lj

DanG · December 04, 2009, 10:40:36 AM

Thanks for the chemistry lesson LJ. We all learn a lot from guys like you who have expertise in areas that are strange to many of us.

Still, I must ask you a question. Would you make wooden toys for your infant Grandchild, and coat them with pure tung oil, knowing that they are likely to chew on them?

The reason I have pursued this is my concern that respected companies like Lee Valley are advertising this stuff as food safe when there is at least a strong doubt about it. When I did the brief Google search on it yesterday, I didn't even have to open any of the links to spot several such claims on the first couple of pages, all from companies selling tung oil. My thought is that most any responsible woodworking Grandpa would feel right proud of himself for checking up on it before using it on toys, and would readily trust the info provided by reputable companies. He wouldn't likely look 3 pages deep in the Google list to find the link I posted.

It would be comforting to know that the product being sold has undergone some process that renders it safe, but we don't know that. It could well be that the poisonous part is a volatile that disappears with evaporation, but I've seen no evidence of that, one way or the other. I have to wonder if the companies have actually investigated, or just took the word of the Chinese company that sold it to them. ???

As I was writing this, it occurred to me that I am distantly aquainted with Dr. Bill Law, who is the head of the Plant Biology Dept. at Fla. State University. I happen to know that he has an interest in matters such as this. I will email him and see if he can shed some light on it. ;)

ljmathias · December 04, 2009, 11:24:05 AM

DanG: good thought on your friend Bill Law- keep us informed on what he says. While I understand the chemistry involved, I'm not a chemical safety expert. I do know, however, that the trend is to consider everything toxic and back off as data becomes available showing something's not. Not a bad way to proceed except for the fact that, with everything toxic, there's not much left to use.

As to my grandkids, well, first of all, they eat bugs and stuff off the floor, so maybe chesing on a toy wouldn't add too much... :D :D Seriously, though, you raise a good point: would I make something for them when they stop chewing on things and finish with tung oil? You bet! Would I give a kid who's teething anything coated with anything at all? Nope, even paint or so called "natural" finishes; mineral oil has been put forth, but that actually used to be a "flushing agent" for kids with upset stomachs- bad side-effects for babies. In fact, would I let a baby chew on a toy made just of wood with no coating at all? No, he/she might chew off a splinter and get it stuck somewhere...

We come down to the distinction between being safe and being careful, but I'll reserve that opinion for a more appropriate discussion. I guess it comes down to which evil you choose and what level of safety and risk is associated with it: it drives me crazy sometimes when my wife and daughter-in-law look at possibilites that are so remote as to never happen in the real world, yet I give in and change the design of the stairs or the upstairs window so that "what if" can't happen no matter how unlikely.

This has been a great discussion and I hope everyone realizes that my opinions are my own and not safe for general consumption. ;)

Lj

DanG · December 04, 2009, 12:08:19 PM

LJ, I appreciate your input on this. I did another Google on "tung oil toxicity" and found that I'm not the only one that is concerned, but nobody seems interested enough to follow up on it. It has been mentioned on a number of other woodworking forums, but has failed to spark much discussion. It'll be interesting to see what Dr. Bill has to say about it.

DouginUtah · December 04, 2009, 12:32:57 PM

I have a book (somewhere in storage) written by a guy whose name I can't recall at the moment (now I recall his name is Michael Dresdner) but he is a woodworker/finishing expert who lives in Puyallup, Washington. In the book he discusses toxicity of finishes and his conclusion is that all commonly used wood finishes are non-toxic when fully cured.

And that's all I've got to say about that! ;D

SwampDonkey · December 04, 2009, 02:54:54 PM

Well I did purchase some Linseed oil today because I know we used it on our bowls and bread knives 25 years ago in shop class. I never made any bowls for food use since. But, this here litre will last me for a very long time. Says not to drink it [like coke though] or feed to animals. :D Folks consume the cold pressed flax seed oil as soft gels. What do you think linseed is? All it is, is French for flax. It's extracted and processed differently. You don't want to know what they want you to dilute it with and applied right on the cutting board or butcher block. :D

I also got some mineral oil and I have no worries about that either. No one around here to chew and lick enough of it to amount to beans.

They had 4 litre jugs of the linseed for $20, this one litre was $10. Boy, how we like to take it. :D

ohsoloco · December 04, 2009, 06:58:46 PM

Brad, the label on that can looks just like the one that came with the cider press. No flaking of that stuff either (so far). It's some tough stuff

BcWoodWorks · December 04, 2009, 10:19:12 PM

Have we reached any definitive answers, as to which finishes are safe to use with cutting boards?

FWW magazine recommends pure linseed oil, not boiled for their cutting board design. As a rookie, planning to make an Christmas present out of this; I would really hate for someone to get sick because I made a serious mistake and got the wrong kind of oil.

Any further information would be most appreciated; although I have to say the previous posts are quite detailed!

Don_Papenburg · December 04, 2009, 10:31:14 PM

Why not just blast the rust out of the cast cylinder , then do your squeezin and then coat it with mineral oil to keep the rust at bay .

DanG · December 04, 2009, 10:39:54 PM

Quote from: BcWoodWorks on December 04, 2009, 10:19:12 PM
Have we reached any definitive answers, as to which finishes are safe to use with cutting boards?

I really don't think it is that big of a deal for items that just come in casual contact with food, like cutting boards. I'm more concerned with things like salad bowls where acidic things like vinegar would be in prolonged contact with the wood, or toys and furniture that small children might chew on. I think the linseed oil will be just fine for your cutting board. Don't make it too pretty though, 'cause they may just hang it on the wall and not use it. ;) :D :D

BcWoodWorks · December 04, 2009, 11:40:15 PM

Quote from: DanG on December 04, 2009, 10:39:54 PM
I really don't think it is that big of a deal for items that just come in casual contact with food, like cutting boards. I'm more concerned with things like salad bowls where acidic things like vinegar would be in prolonged contact with the wood, or toys and furniture that small children might chew on. I think the linseed oil will be just fine for your cutting board. Don't make it too pretty though, 'cause they may just hang it on the wall and not use it. ;) :D :D

My apologies Dan, I should have read a little more deeply than I did. I didn't realize such small things like vinegar dressing could affect the finish! Just goes to show, when you're a rookie...You're reaaaaally a rookie. :D

Don't worry about it being too pretty, I'm just aiming for it not being firewood for Burlkraft's stump pile! ;D

Good posts, by the way DanG. Truly well sided.
-Alec

DanG · December 05, 2009, 12:54:10 AM

Well thanks BC, but I'm a rookie too when it comes to things like this. In fact, it is my ignorance that makes me cautious, overly cautious at times I'm afraid. :

You see, I have no training in chemistry at all, other than the tidbits I've picked up here and there over the years. You could say that I have just enough knowledge to make me dangerous, but I prefer to think that I have just enough ignorance to make me safe. I have no idea just what acids might react with what oils to release toxins that are supposedly locked in by some curing process, so I try to avoid those that have toxins in the first place. Tung oil, for instance, is made from a known toxic plant. I'm sure it is quite safe for casual contact, but what effect will flooding it repeatedly with apple juice have on it? I don't know, you don't know, and Brad doesn't know, so he would be well advised to not use it on his cider press, in my way of thinking.

As far as I know, the linseed oil will be just fine on your cutting board, and I've never heard anything to the contrary. Mineral oil or olive oil would be other safe choices, as none of them would hurt anybody if they did leach into the food.

Lud · December 05, 2009, 08:32:12 AM

I've avoided using olive oil as I've heard it can go rancid......besides I don't like olives.

Mineral oil and beeswax is my choice so far. My wife stacks the bowls she uses with paper towels between them that have the mineral oil she's reloaded the bowls with. Y'see, that's the problem with mineral oil...it leaches away and you should reapply to bowls being used regularly.

"Once a month for the first year and then as needed" is some old wisdom I've heard.

I wonder if anyone has tried running a vacuum on a bowl in a bag full of mineral oil? I'd bet that would get penetration by sucking the air inside of the bowl out and sucking the oil in deeper.

Brad_bb · December 05, 2009, 11:58:39 AM

Don, the basket in that photo consists of an outer sheetmetal ring that is soldered at a vertical seam that forms the loop. I'm sure lead solder. The inner basked is perforated sheetmetal ring again soldered at a vertical seam. The basket is not cast, only the base and upper screw bracket and handle. When I did blast the cast parts, there was what appeared to be solder on them too. I think they used solder to "bodywork" the castings before painting. I blasted some of it off, but that which did not come off, was covered/sealed by the epoxy primer and will be with paint and food safe epoxy as well.

It seems like there is consensus on Mineral oil being safe. Linseed seems to be about 50/50, Tung oil doesn't seem like many agree, and Olive oil, while safe to ingest while it's good, does go rancid eventually and therefore I would not use it.

Mooseherder · December 05, 2009, 12:08:26 PM

We use Mineral Oil for our Grinder Plates, Knives and Grinder Worm Gears at our SuperMarkets because it is food safe and won't go rancid. The equipment is cleaned and sanitized daily so the oil serves more of a lubrication to slow down bare metal rusting after production is finished.
These parts seem to rust overnite if we don't use mineral oil. :

A case of 4 gallons lasts over a year even using it daily. We dispense it in spray bottles.

I wouldn't use oil that has an opportunity to go rancid on food contact areas.