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

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Q. I work for a restaurant chain that is switching from plastic cambros to all stainless steel. They seem to believe a myth that tomato acids react with stainless steel. I have already disproved this myth.

Now they are saying that our guacamole (which is made with a touch of lemon juice) will react to stainless steel and become discolored. I disproved the color theory yesterday. Now they are saying it is a slight taste difference. I think it taste different because they want it to and their mind is telling them it does. The whole reason behind the argument is that we are using plastic liners in the tomato products and guacamole pans. I am trying to eliminate the use and save the company money. The proof they want seems like they want me to prove there is no such thing as Bigfoot, when there is no proof that he actually exists.

Chris Milazzo
Restaurant - Winter Park , Florida


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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.

Lee Gearhart
metallurgist
East Aurora, New York



September 18, 2009

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.

Cliff Kusch
electropolishing shop - North Vancouver, British Columbia, Canada



March 3, 2011

thumbsup2Appreciate the replies here! I stumbled upon this why 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.

George Francis
- East Greenwich, Rhode Island USA

DFL Water Bottle



March 20, 2011

Q. Yesterday, I made a lemon curd to top a cheesecake. The process involved cooking lemon juice and sugar together for several minutes. Instead of using a non-stick pan that I have used several times in the past, I used a stainless pan that is supposed to be non-reactive. When the cheesecake was tasted, I noted a metallic taste that was not present in earlier cheesecakes. Although stainless steel is non-reactive for most cooking applications, it is still a steel alloy. Will an acid such as hot lemon juice leach iron from stainless steel?

I'm thinking that I should look for a pyrex sauce pan for cooking acidic foods.

Ralph Guymon
Cooking enthusiast - Orange, California, USA

January 22, 2012appended

Q. I've been hooked on lemonade for awhile. I have to use plastic bottles to drink from because I have Multiple Sclerosis and I spill a lot. Today I purchased a stainless steel sports bottle from L.L. Bean because the plastic bottle becomes cloudy after a few refills (is the cloudiness from plastic dissolving or from the lemon bleaching?). Did I make a mistake? Will the stainless react with the lemonade?
Please answer quickly--I might have to cancel an order.
Dona

DONA SALTER
- SOMERS PT, New Jersey

January 23, 2012

A. Hi, Dona. It's a public forum; people may not see and respond to your posting for weeks or months. Fortunately, L.L. Bean has an unconditional moneyback guarantee: "We do not want you to have anything from L.L. Bean that is not completely satisfactory".

But we appended your inquiry to a thread that may already answer it for you.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


Kombucha brewer needs documentation that fermenting tea won't leach type 304 Stainless

March 19, 2014

Q. Hi - I am a Kombucha brewer and trying to get my fermenting gear approved by my department of agriculture inspector. Stainless Steel is the norm used without incident by many brewers around the country but this is new territory in my state. I'm looking for someone with a knowledge of metals to verify that the pH of my product is safe to brew in 304 grade SS - he is concerned about possible leaching and wants some sort of documentation that states it will not be an issue. The lowest possible pH would be 2.5 but in reality it will not go below about 2.8. Is there someone in the metallurgy field whom I could hire to write a document stating that this would not be an issue.

Kind regards,
t

tonya donati
- st petersburg, Florida USA


March 25, 2014

A. Tonya,
I can't quote chapter and verse to you, but the FDA has long approved of 304/316 stainless steel as a safe material for contact with pretty much everything. If you can track down a citation I would hope that would trump your state department of agriculture.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois



March 28, 2014

A. Google search to the rescue!
Here is a fairly fun paper to read on the corrosion of stainless steels of varying flavors.

"CORROSION RESISTANCE OF THE AUSTENITIC CHROMIUM-NICKEL STAINLESS STEELS IN CHEMICAL ENVIRONMENTS"
http://www.parrinst.com/wp-content/uploads/downloads/2011/07/Parr_Stainless-Steels-Corrosion-Info.pdf

If that's not enough to put you to sleep there is another paper that has MANY good references on corrosion and Stainless Steel:

"Corrosion in the Food and Beverage Industries"
ftp://63.174.97.22/pub/MARC_Records/V13c/asmhba0004202.pdf

Now I'm handing you these papers rather than an easy answer because they provide some very good and reliable baselines (especially the first one) for when 304 is going to start to react (remember Acetic acid = vinegar). Both of the above are from peer reviewed journals.

Generally I think you're getting a bit too much concern from this inspector regarding the tank material. It should be held to the same standard as any beer or wine brewing setup.

Marc Banks
Blacksmith - Lenoir, North Carolina USA



July 20, 2014

Q. I got a "stainless steel" cup from Starbucks, but there is no mark on the cup indicating the "grade" of stainless being used. Does this mean it is actually aluminum? A magnet does not stick to it. I drink water with lemon oil every day. I have been told NOT to use plastic because it will break down petrochemicals. I have been using glass, but thought the tumbler I found would be a great alternative. How do I know what type metal is being used and if it is ok? Thank you.

S Cleveland
- dallas, Texas usa


July 2014

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 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 you can surely easily tell from the Archimedes experiment. Good luck!

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

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