Restauranteur asks if stainless steel okay for lemon juice (citric acid)?

A. Hi Chris.
I think the source of that idea might be that aluminum (not stainless steel) can be sensitive to such acidic foods. Since many different product lines may use either metal, and they look vaguely similar, many people probably don't pay much attention to the difference :-)
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Chris, as a metallurgist with almost 25 years experience dealing with stainless steels, I'm in your corner. You'd better not serve anything that will attack stainless steel, as that substance will quickly and dangerously corrode the palates of your diners :) Nor can I believe any food or beverage will leach out metal from stainless, affecting the taste of the product.

That said, there are different stainless steel alloys. Pans, sinks, and some flatware are made from the 300 series, so-called "18-8" varieties, which have quite good corrosion resistance. The cutlery grades like 440C are used to make knives, because it gets hard and keeps an edge: yet its corrosion resistance is much less than the 300 series grades, and it might show rust if you left it in salt water for a time.

You've also got to be careful about scrubbing the stainless steel with a Brillo pad, or any other steel wool contact. If those plain steel fibers imbed in the stainless, they'll rust and take the surrounding stainless steel with it. Perhaps this is the source of your co-workers' concerns?

One last thought regarding the taste issue: I'd find it far easier to believe that plasticizers, dyes, UV inhibitors, and other additives to plastics can theoretically leach out into food or beverage, than metallic ions from stainless steel, especially as time and temperature cycles from cleaning march on.

A. I agree with Lee. As long as the stainless steel you are using is not contaminated with iron, ferric oxides, etc., and is not "rusting". The stainless will not change the color or taste.
To obtain the highest quality pure finish for stainless, have your parts electropolished. This will remove all contaminants and leave the surface ultra-clean. Also if you can, demand at least 304 or more preferably 316 stainless steel.

My suspicions are that your "tasters" have gotten used to the leached plastic taste in the food as opposed to the REAL taste they are missing if they were to use leach free food prep equipment.

Appreciate the replies here! I stumbled upon this while googling "stainless steel" and "lemon", together, as I have a "Designed for Living" stainless steel water bottle, and was wondering whether my adding a couple of lemon wedges into my water would introduce any type of corrosive affect on the interior of the bottle.

From the replies I see here (perhaps contingent on the grade/type of stainless), I shouldn't worry. Thank you.

A. Of course, Stainless Steel Lemon Squeezer is safer than others. As my opinion, Stainless steel is best quality material for making any squeezer and it's also durable and long-lasting. Stainless Steel is very hard & smoother than other squeezers. It is easy to hold & very comfortable for the manual press.

A. Hi Ralph. Did you taste it with your fingers or use a fork? The only times that I personally have experienced a metallic taste is with silver plated flatware that is worn. The underlying nickel-silver substrate has a strong metallic taste if the plating is worn through in a spot. I don't think iron has a metallic taste.

Regards,

A. Hi, Dona. It's a public forum; people may not see and respond to your posting for weeks or months, but we appended your inquiry to a thread that may already answer it to your satisfaction.

Fortunately, L.L. Bean has an unconditional money-back guarantee: "We do not want you to have anything from L.L. Bean that is not completely satisfactory", so if someone eventually convinces you that there is cause for worry, you can return it then :-)

Regards,

A. Hi, S. When you say it was "stainless steel", do you mean it looked something like stainless steel to you, or that it was actually advertised or labeled as stainless steel? I'm sure Starbucks wouldn't lie about such a thing. And I'd bet that they, like almost every other manufacturer, has an 800 number that you can call to find out. Stainless steel weighs nearly 3x what aluminum weighs, so you may be able to tell just from the heft, but if it's not a hollow thermos bottle you can surely easily tell from the Archimedes experiment. Good luck!

Regards,

A. The stainless steel of type 316 is an austenitic chromium nickel stainless steel containing 2% molybdenum. this addition increases resistance to pitting, and provides increased strength at elevated temperatures. Corrosion resistance is improved particularly acidic medium such as sulfuric, hydrochloric, acetic, formic and tartaric acid.
I would guess that your problem would be solved using stainless steel of type 316 or 316L.

A. While this doesn't directly pertain to acidic foods on stainless ware, it is an important thing to note in rare cases: Be careful about mixing different metals with foods. If you put tinfoil over a steel pan for instance, it may use the food as an electrolyte and create a crude battery (power cell technically.) This can greatly accelerate the reaction between pan and food and you may even see a blackish residue leeching from one of the metal surfaces into the food.

A. Two studies:

Ed. note: Thanks Doru. Readers: the link for the second article is to the abstract only; the actual article is behind a pay wall

A. I just wanted to mention, with regard to the 2 studies posted in the last comment - The first PDF had some great information on corrosion; however, looking closely at the grade of stainless steel on which the study was done, I found "stainless steel grade 201" (bottom of page 3) as well as "Cr 16-18% / Ni 3.5 - 5.5" in the chart immediately following.

The concluded leaching rate in report #1 should not be compared to cooking grade stainless steel of 304 (18/8), 302 (18/10) or 316 (18/10 MO)(surgical grade) because the rate of corrosion in reported grade 201 is MUCH higher than what we normally use in our kitchens.

I have no comment about the second report because I will not be paying $40 for 48 hours of access to their website, but I can only assume that the posted excerpt of findings is along the same lines and has been gathered from a much lower grade stainless steel.

If anyone has similar reports on grades 302, 304 and 316, I invite them to post a link :)

C. Weppner
- Las Vegas, Nevada
December 2, 2016

opinion! Hello C.
I won't pay $40 for 48 hours of access either! As a society we need to figure out a good way to compensate researchers for authoritative work, but charging for temporary access to technical info is reckless!

How does it feel knowing that your doctor no longer has access to the electronic textbooks rented to her while she was in school, so must choose between guessing from memory what they said or paying $40? How do we like driving over a bridge designed by an engineer in the same situation    :-)

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 2016

P.S. June 2020: We can be heartened that negotiations between M.I.T. and Elsevier have broken down; my limited understanding is that M.I.T. will not let Elsevier continue to have that sort of control over the research they have done.

opinion!  The fees asked to access academic papers is a disgrace and impedes the progress of knowledge.
However there is frequently free access by simply running a search on the full title. Hence
1. http://www.electrochemsci.org/papers/vol10/100503792.pdf
My main comment is that this refers entirely to type 201 stainless which I would not regard as a standard food grade.

2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284091/

I come from a time before the atomic absorption spectrophotometer ⇦this on eBay or Amazon [affil links] . Since they arrived on the scene we have been inundated with more and more data on trace elements that are rarely significant outside academic circles.
As an old chemist with an interest in toxicology, I have no idea what my SS pots are made of and no intention to ask.

It is probable that the 'metallic' taste some people experience is due to an electrolytic cell set up between the cup and the body (metallic fillings would enhance the effect).

Geoff Smith
Hampshire, England

Ed. note: Geoff's 2nd URL does indeed work to offer free access to the 2nd article suggested by Doru

A. Hi Robin. Although anything is possible, I'd suspect a long list of more probable things before considering that possibility, and I bet that someone with medical training would agree :-)

Regards,

A. Billy,
If the stainless really is leeching iron into the water, just fill the container with a solution of at least 4 weight percent citric acid and let it soak for at least 30 minutes. (Or partially fill it and rotate the container so that all surfaces have at least 30 minutes exposure to the solution.) Rinse it out with water afterwards and let it dry in air overnight.

A. Here's an article about stainless steel grade 316 leaching nickel. It's free to read.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284091/

Ed. note: Thanks Mackenzie! This is the same URL that Geoff & Doru suggested. Great minds etc.

A. I am Robert Seals the inventor of Klean Kanteen which started the stainless vs plastic revolution; I sold the company years ago. I had the bottles tested back then because as a metal worker I was concerned about electropolishing, which I did not trust. Using an acid equivalent to lemon juice it was found to leach nickel over the acceptable amount allowed by FDA standards. I was concerned enough to print FOR WATER ONLY on the bottles as the same tests showed no detectable metal when water was used.

Electro polishing is not the way to passivate any food container. The old fashioned polishing method is by far is the best way to seal the metal but it's too labor intensive for production. The public is being duped on this one.

  Thanks Robert. Maybe stainless steel isn't quite as impervious to acidic food & beverage service as we thought? What grade of stainless did you use?

But I'm not understanding your point about electropolishing at all, which I understand to be the only safe & accepted way to polish pharmaceutical and dairy equipment. Are you saying that you have found that mechanically polished surfaces leach less nickel than electropolished surfaces? If surfaces are mechanically polished, what passivation method do you feel is indicated?

Thanks again, although without any data I cannot concede that electropolishing leaches more than mechanical polishing.

Regards,

A. It's an interesting topic. We have data showing that citric acid exposure does not remove chromium or nickel from the surface of stainless, in order to show that citric acid passivation has a lower waste disposal task than nitric acid passivation, which definitely removes some amount of chromium and nickel.

I rather suspect that even "highly acidic" foods are closer in acidity to a citric acid passivation bath than a nitric acid passivation bath. However, I would eagerly read any further studies performed using lab or real-world conditions.