Smells and Stainless Steel

I’ve been a Cecil loyalist for some time now, but with his 18-Jun-1999 column, my confidence has been sorely tested.

Regarding specifically his piece about the ostensible deodorizing properties of stainless steel:

My guess is that Unca Cecil and Larasaurus have fallen victim to one of the most common logical fallacies around: assuming that just because B followed A, A caused B. Sure, things often happen just that way, but there are times when A has nothing at all to do with B.

The probable explanation for what they experienced is the psychological effect called “acclimation”, which roughly means “getting used” to something; in this case, a strong odor. I’m sure we’re all familiar with experiencing strong smells on occasion upon entering someone else’s home, which before too long we unconsciously adapt to and can no longer readily detect. I strongly suspect that this is the key operating principle in the “amazing stainless steel de-stink scenario”.

If I recall my psychology correctly, the stronger the offending sensation, the faster the acclimation process, but I could be all wet about that part. Nevertheless, there is no doubt that Larasaurus’ pal Jonathan would have become less and less objectionable over a fairly short period of time, stainless steel or no.

In short, Cecil, your theory stinks!

There may be more to this story. Stainless steel is also supposed to help with the eye irritation caused by onions. I’m pretty sure (sorry that I don’t have a real reference for this; I am not claiming to know all, just tossing this out) Consumer Reports magazine recently ran a short bit about a chunk of steel being sold for this purpose. Their conclusion was not “this whole thing is stupid”, but rather on the order of “the steel seems to help our eyes, but you don’t need to buy a special chunk; use any steel object such as a knife”

I do not think they had an explaination for how it worked.

Incidentally, I feel the need to comment that stainless alloys do not generally show ferromagnetism (the phenomenon that, among other things, accounted for a chunk of metal being attracted to a horseshoe magnet). Thus, the illustration to this week’s column is inaccurate.
I doubt that anyone looks to Signorino’s drawings to provide them with True Insight. However, if anyone feels like batting Slug around a little, this probably provides as good an opportunity as any.

“Kings die, and leave their crowns to their sons. Shmuel HaKatan took all the treasures in the world, and went away.”

Perhaps a more systematic study is in order. Both onions and garlic get their characteristic smells from thiols or sulfides - sulfur containing compounds. Both thiols and sulfides can react with, or coordinate to, metals. I could not tell you which metals sulfur prefers in the stainless, but the reaction/coordination would certainly account for the effectiveness of garlic and onion odor elimination.

Of course, one would have to test this against other classes of smelly compounds - namely amines and other nitrogen-containing compounds (like in fish) and fruity smells, which are usually methyl or ethyl esters of short chain acids, as well as other smellies with only C, H, and O (alcohols, acids, aldehydes and ketones).

So, I don’t think that the whole theory is bunk - one just needs better controls. For that matter - many other metals should work, but stainless happens to be cheap to manufacture.

Thanks, Xray for coming to our aid – a knowledge of chemistry is just what we need!

Speaking of a “more systematic study”, I managed to come up with a home-grown design for an experiment. Although I had no idea which chemicals were involved, I knew that odors are molecules from various source carried through the air. From this it follows that for stainless steel to dramatically reduce an odor, it would have to be as a result of a chemical reaction between the molecules of the odor and the wet steel. (I realize you’ve already said that and this is very basic; I’m just setting up my experiment).

So, to test the theory, I dug out a couple eye droppers and some litmus paper I found and measured three identically small sample pair sets, each pair consisting of a vinegar and a lemon juice sample each with six drops of tap water added (six samples altogether). One pair went into clean glasses as a control set, one pair I carefully poured over flat areas of a dry porcelain sink, and the third pair I likewise poured into a dry stainless steel sink (well away from the drain in both cases). Then I’d test each sample with the litmus paper.

The results? I could detect no differences in the litmus colors from the three vinegar samples; likewise in those from the three lemon juice samples. I could try a base like ammonia if you think it might be worthwhile (but I hate the smell!)

I realize that what this proves is rather limited. At most it proves that the combination of stainless steel and water has no effect on the pH of either of these acids. And while I acknowledge that the purported odor-reducing reactions might not effect pH, in my own admittedly layman’s mind that seems unlikely. But you’re the chemist: am I way off base here? (yuk, yuk)

An maybe you can clear up something else about stainless steel for me: I always thought that one of the benefits of using it was that it resisted most chemical reactions. Surely such an insignificant concentration of chemicals as would be present in an odor couldn’t overpower s.steel’s resistance to reactions, could it? Enough to substantially neutralize so many of the odor’s molecules

ambushed - you bring up interesting questions and hey! someone who finally gets up and does their own experiments!

Stainless steel can certainly be “in general” unreactive. But all bulk materials will have their crystal defects, strange metal inclusions and the surface is NEVER pure. There is usually a few Angstroms of oxidized material on the surface of everything. My sulfur theory comes from the prevalence of making molecular monolayers on surfaces using thiols, sulfides and disulfides. All one needs to do is take some thiol in solution, place it on certain metal surfaces and Whammo! Covalently bound (through the sulfur atom) molecules on the surface.

One hallmark of living in an oxygen contain atmosphere is, well, eventual oxidation. After a certain time, the bound molecules could be readily oxidized in presence of UV light and oxygen.

As for your experiment with the acids - either the -COOH portion is not reactive with the stainless steel or the concentration was way too high. If stainless is as “unreactive” as one would hope, then a very small amount of functional groups would react with the surface, leaving the rest to float in solution - thus the positive litmus test.

As for the base experiment - it would probably yield similar results - you would saturate the surface quickly and would still have a lot of ammonia in solution.

So, we are so far left with hearsay and anecdotal evidence. Ugh - without my morning stimulant infusion, my brain is useless. When I have something intelligent to add, I’ll get back to you.

Coffee!!! someone send me Coffee!!

Thanks for your reply, Xray, and for enlightening us a bit more about stainless steel. But after you’ve downed this morning’s dose of roast, perhaps you’ll clarify something you said in your latest post:

OK, I think I understand about the concentration. What you’re saying is that even though I used very small amounts of relatively dilute concentrations in terms of “kitchen” standards, the s.steel might have been unable to react with enough of either of the acids to make any measurable difference (at least with litmus paper). If that’s true, of course, we can all forget about testing the s.steel deodorizing theory outside of a laboratory. (Cecil’s and Larasaurus’ experiments don’t qualify either, since they fail to eliminate acclimation effects and the purely subjective nature of their “measurements”).

But as for the first part, that maybe “the -COOH portion is not reactive with the stainless steel”, isn’t that just another way of saying “your experimental results may well count as a strike against the s.steel theory”

my brain’s still not functional - but I’ll take a stab at your last point, ambushed.

Different chemical functionalities (-SH, -NH2, -COOH, -COOMe etc.) will have different affinities for the metals in the surface. A thiol group (-SH) will have a different affinity for a given surface than a -COOH group. It has to do with (among other things) electron density/dipole moment or _____ (insert other interactions here: van der Waals…).

So, there are a couple different ways to explain your results: 1) concentration was too high 2) -COOH has a different affinity for s. steel - and since garlic and onion smells don’t come from -COOH groups, has no bearing on the anti-garlic properties of s. steel or 3) s. steel doesn’t work as any sort of odor-elimination device.

Without mass spectrometry or reflectance infrared spectroscopy, it would be difficult to really probe the surface for bound thiols/sulfides…(or perhaps their oxidized equivalents…)

Wow! “Xray” blew me away with the sulfurs angle. I was thinking more along the line of oils being somehow attracted by the stainless steel. All I know for sure is that it does indeed work. The old restaurant worker trick of scrubbing silverware (the stainless kind) to get rid of the smell of onions translates nicely into the shapely little bars they sell through Williams-Sonoma…

A little while ago in this thread, Akatsukami wrote:

“Incidentally, I feel the need to comment that stainless alloys do not generally show ferromagnetism (the phenomenon that, among other things, accounted for a chunk of metal being attracted to a horseshoe magnet).”

After reading this, I went home and held a refrigerator magnet up to one of my stainless steel teaspoons. The magnet stuck just as well to the spoon as it did to my refrigerator door. Felt pretty ferromagnetic to me.

So, was my teaspoon only stainless-steel PLATED with ordinary Stainful Steel at its core, or what?

It must be, Tracer. I have a stainless steel plate in my arm (from a roller blading accident) and it is not magnetic. It has never even set off a metal detector at airports.

“I had a feeling that in Hell there would be mushrooms.” -The Secret of Monkey Island

Don’t get so carried away, Chris in Stockton, CA! Even though Xray clearly knows his chemistry, he was only speculating about the possibility of a theoretical mechanism whereby stainless steel might possess the properties you and others allege. Please review his post just ahead of yours, where he acknowledges that stainless steel might not have any deodorizing effects!

The jury’s still out, Chris… You think stainless steel has this power. Cecil thinks so. Larasaurus thinks so. Xray might (or might not) think so. But neither I nor the (admittedly small) group of people I’ve asked about it agrees. Nevertheless, such matters cannot be settled by vote! Careful experiments are needed.
Speaking of which, I have a new design for an experiment that might help decide the issue. I’d appreciate any help in uncovering any methodological flaws before I perform the experiment…

  • Obtain and label 20 Q-tips and prepare a data sheet for them.

  • In a separate room (actually, I was planning on doing this outdoors), prepare a mixture of garlic and water (would garlic powder work?). This will be used as the source for all the samples.

  • Dip all of the Q-tips in the garlic “juice” so that the cotton is just submerged for each of them.

  • Take half of the Q-tip samples at random and apply the tips and all sides of each of them to stainless steel for ten seconds. Record which were exposed to the s.steel on the data sheet.

  • Instruct your test subject(s) to smell each of the Q-tips one at a time and record whether they report a stronger or weaker odor of garlic. Then leave the room while they carry out these instructions to avoid biasing the results.

  • Tabulate the results. If the subject(s) pick the s.steel treated samples roughly half the time, then the null hypothesis (i.e., that stainless steel has no effect on garlic odors) has been considerably strengthened (and established, for my purposes at least).

Whaddya think?
By the way, bohrer: any chance of finding that Consumer Reports article you mentioned? I’d like to take a look at that article…

Psst!!! Xray is female…

as for the experiment - first I would make sure that garlic odor is soluble in water. Secondly, I’d try filter paper as opposed to Qtip. Qtips have a hell of a lot of surface area. I think that small strips of filter paper would better emulate the skin’s surface.

As for design flaws - you have not nullified the “accustomization” problem you mentioned in your first post. Smelling 20 q-tips - with half of them treated - is still a heavy garlic dose. So, in this way, the study is still biased.

I could imagine doing a gas chromatography experiment for this - it’s simple and one doesn’t need the mass spec. but one does still need a GC. Actually, I’m intrigued now. Maybe this weekend I’ll do my own experiment and use the Institute’s GC for this purpose (don’t tell anyone, though :wink: )

So, ambushed, before you go through the trouble of starting the experiment, I would hold off - you are already biasing the results against s. steel working.

Sorry, Xray! Even though gender-neutral language can often be rather awkward, I usually try to use it anyway. I clearly need to catch myself and try harder, since I sure slipped up here. Just the other day I tentatively wrote “(her?)” in a reply to another poster I greatly respect, only to be chastised for getting his sex wrong also…

Thanks for critiquing my experiment. I knew that the acclimation problem would remain, so I should have mentioned that I expected a descending slope in the results. (But on second thought, that would have been very difficult for me to compensate for). Clearly, the experiment wouldn’t have worked. So I’d be delighted if you were able to test the theory more rigorously, as you propose! (I’ll never talk!)

By the way, I came across an article on the web that pokes fun at a product consisting of a small piece of s.steel that’s alleged to remove all kinds of odors, not just onions and garlic. I contacted the distributor that sells the thing and requested references or test results or anything else that might back up their claims. (For what it’s worth, I could find no other references to the alleged deodorizing properties of s.steel anywhere on the whole Internet.)

I was duly impressed when they replied via email that they would pass on the request for scientific data to the actual manufacturer, and guaranteed that they would have a reply for me by July 6. I really didn’t even expect them to answer me at all! This may bode well for the theory…

Anyway, thanks for taking the trouble to help with this question, and I appreciate your time and efforts!

tracer writes:

Well, I went out and did a survey (by no means complete, I concede), both of firms that produce SS alloys, and of firms that manufacture kitchenwares.
The firms that produce alloys emphasized that their alloys were non-magnetic. The firms that produced kitchenwares emphasized that they only used non-magnetic alloys in their construction. Producing a magnetic SS alloys seems to be considered gauche, and actually using it appears to be a definite no-no.
OTOH, from the emphasis placed on this, it may well have happened that someone did, at one time at least, produce a ferromagnetic alloy that could be considered stainless, and that someone else picked it up and made, say, spoons out of it. I suppose I can’t (and didn’t) say, uncategorically, “No stainless steel alloy has ever exhibited ferromagnetism.”
I’ll see what additional resources can be brought to bear on the problem.

“Kings die, and leave their crowns to their sons. Shmuel HaKatan took all the treasures in the world, and went away.”

The cutlery in my kitchen is a hodge-podge of mismatched items from different makers and they all are magnetic. They all say “stainless” on them. (Not “stainless steel”, just “stainless”, but what other stainless metal could they be?)

There are alloys of stainless steel that have magnetic properties. I take it as a matter of faith Cecil informed Ed to inform Slug to use a cake of one of these alloys as a model for his illustration.

“Stainless” steels are not really stainless at all. The alloys are designed to attract and bond very forcefully an oxidized layer that does not “discolor” the steel. This layer, being very tightly bound, prevents other, more unsightly compounds from attacking the steel itself.

However, the oxidized layer does discolor the steel somewhat, and stainless steel polishes are available for removing it. Which, of course, defeats the whole purpose. Any similar methods for cleaning stainless (dilute phosporic acid, say) will provide that “bright shiny” but strip away the protective coating. You can’t have both.

I think the stainless flatware you people are talking about is chrome plated.

Update -

I’ve spoken with another colleague, who is equally intrigued about this question. The two of us will set up an experiment and try it on the GC, though it probably won’t be until the end of the week (owing to that annoying thing called a “thesis” Bah!)

I’m still writing up the experimental - we need three controls (to take the running water into account) and probably four separate samples. But, over a few beers on Saturday, we figured that it would probably work. When I get the experimental written, I’ll post it here.

I found this link while looking for skunk spray remedies:
While this link is a about skunk spray (“thiols and acetate derivatives of these thiols”), Xray may find some of the information useful in her experiment design. I found his discussion of tomato juice and olfactory fatigue particularly relevant to this discussion.

I did my own, single sample, exeriment as well. I applied garlic to my son’s finger, had him smell it ,washed it under water with a piece of stainless steel and had him smell it again. He couldn’t smell anything, but I could. I avoided smelling it the first time. Later he was also able to smell it as well. The smell was not as strong as the smell of freshly applied garlic, but it was there. I should note that my son is 5 years old, and thus does not have any opinions on this subject. The piece of stainless steel was a large french chef knife. There was a fair amount of friction between the skin and the knife which leads me to wonder if a pumice stone would work even better.

I think in light of the previous experiments that the composition of the “stainless steel” needs to be known.
There are all manner of alloys that fall under the loose term of “stainless steel”. Some actually contain steel, hence the ferromagnetic reaction, but some are alloys of copper and nickel and contain no steel at all. What particular metals were in the alloy that the fantastic odor cancelling claims were directed at?
That, at least, must be cleared up before proceeding any further with active testing. Also, the term “stainless steel” should be used ONLY for the alloys of steel that are stainless. Nickel/copper should be referred to as just what it is! “Nickel/copper” or NiCu.