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topic 13743

Maple Syrup Boiling / Evaporator Pans: use Mild Steel or Galvanized or What?

Current question and answers:

February 25, 2021

Q. Hello, I have a large Cast Iron Cauldron similar to those described in this thread. Roughly 4 foot diameter at the outside rim and 2.5 feet deep. The cauldron was previously used as a flower box, and had 9 holes drilled in the bottom for drainage. We had the holes welded closed, and it now holds water. However, the inside of the cauldron was painted with some sort of powder coat which could not be easily removed with sand paper, heat, or even a disc grinder. So we had a local shop sand blast the inside surface to remove it. We want to boil sap in the cauldron, and ironically enough I have sap ready to go as I am typing this (those 40 degree temps crept up on us). I just got the cauldron back from the shop two days ago, and I am wondering if I am good to season it with crisco at 500 degrees as described above? And then boil sap in it the next day? Any help is appreciated. Right now, the bare cast iron is susceptible to rust I fear, as even a small drop of water stains the surface in a light orange hue.

Tom Bachmayer
- Milford Michigan
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Previous closely related Q&A's starting in:


Q. I was reading in a old maple syrup making handbook that for the average maple syrup making hobbyist, and just for syrup for the family, that you could use galvanized wash tubs as a evaporator pan. It would be over an homemade firebox, outside. Would this be a safe practice to use a galvanized wash tub for this?

Rodney [last name deleted for privacy by Editor]
hobbyist - West Michigan, United States


A. It depends on the status of the galvanize and on your opinions regarding "safe". There are some very informative letters about galvanized grills and smokehouses in the archives; if you use the search engine here on the site you should be able to find the answer to your question.

The galvanize itself would be okay (I think - I'm not a galvanizer and do NOT speak as an expert), but a lot of times the parts are coated with a top layer of chromate - which often contains hexavalent chrome, a very bad thing to have in contact with food. Like I said - use the search engine.

Good luck!

Jim Gorsich
Accurate Anodizing Inc.
supporting advertiser
Compton, California, USA
accurate anodizing banner


Q. I have constructed a 2'x 3' pan out of mild steel to use as an evaporator for maple syrup. Other than the obvious corrosion problems related with mild steel, should I be concerned about any contaminants coming from the metal? This is not being used for commercial purposes this is strictly for our home use. I have a 4 year old daughter who loves maple syrup and I want to be perfectly satisfied there is no danger. Please, do not take offense but whomever answers, could you please state your technical qualifications.

Sean Patrick McGuire
- Ottawa, Ontario, Canada


A. Hi, Sean. People eat off of cast iron pans & griddles all the time; they bake on steel cookie sheets; they picnic publicly, grilling hot dogs on steel fireplace grates. They continue to use nickel plated serving spoons and utensils long after the nickel is worn off and the underlying steel is rusting. They carve their turkeys with steel knives. Some of us receive our water through steel pipes. So I wouldn't worry about making syrup on a steel pan.

But if someone wants to look for reason to worry: How do we know it's truly mild steel and not leaded steel? Or that it wasn't cadmium plated and incompletely stripped? Or that the sheet was once used as a part of an Agent Orange spreader or as a drip pan for a PCB transformer? In other words, no matter what qualifications someone has, they cannot issue any guarantees from a distance. But if it's plain steel, and clean, odds seem very good that it should be just fine. Good luck.

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


A. Sean, I assume you're worried about what might leach out of the mild steel into the maple syrup. You shouldn't be. I've got baking pans made out of mild steel, and a couple of nice sharp knives that are made out of high carbon steel, and possibly a few more kitchen implements. I've got a favorite frying pan made out of cast iron- think mild steel with 2% instead of 0.2% carbon, and you're not far off. You probably have some pots & pans made out of non-stainless steel as well. Yeah, the stuff rusts ... so keep it clean, keep it dry, and it will serve you well.

I've been a metallurgist since '78, and have worked in the automotive and aerospace industries, and I've been eating since long before then.

Have fun!

lee gearhart
Lee Gearhart
metallurgist - E. Aurora, New York


Q. I have some galvanized metal evaporator pans and wondered if there is any health concerns in boiling maple syrup that will be used by my family.

Chris Haggith
consumer - Brockville, Ontario, Canada

A. Hi Chris. Galvanized means coated with zinc. Zinc is not a toxin ... in fact it's an essential nutrient.

But there is concern about "overdosing" on zinc because it dissolves pretty readily both in acids and in strong caustics, so zinc is not considered "food-safe" as a general purpose surface. Further, some galvanized metal was treated with a very low-concentration of hexavalent chromium -- which is a toxin and definitely not food safe. Finally, galvanizing, especially old galvanizing, could include more lead than you would be comfortable with.

It's possible that a given sheet of galvanized is free of hexavalent chromium and low in lead, and that it will not be subjected to acid or alkali when used to boil maple syrup; so if you bought something specifically marketed as a syrup boiling pan it's probably fine. Further, although tin coating is not as common as zinc plating, it is available and looks a lot like zinc plating, and it is food safe; so it's possible that boiling pans purchased for the purpose are actually tin plated.

My answer is that if it was an item sold for the purpose, I'd use it. But I wouldn't simply take a sheet of galvanized steel and form a boiling pan out of it. Best of luck.


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

March 29, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I was think of using some galvanized tubs to boil sugar maple sap into maple syrup. Do you think this would be a health hazard?

Richard Martin
- Utica, New York USA

April 1, 2013

A. Hi Richard. I don't like to use the word "hazard" because hazards ought to be quantified (because everything is hazardous to some degree) and nobody can say exactly what the danger is and how severe it is. So I'd prefer to simply say that galvanized surfaces are not food safe so I think they should not be used for this. Stainless steel would be ideal, but plain steel or aluminum would probably be better choices than galvanized. Good luck.


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

April 9, 2016

Q. How about using a copper kettle for boiling sap over a fire out back? Does anybody know of potential drawbacks to using copper?


- Norman

Norman Carter
- East Montpelier, Vermont, USA

simultaneous April 11, 2016

A. I'd use a stainless steel vessel.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

April 11, 2016

A. Hi Norman
Copper cooking pots are good enough for many of the top chefs of the world. Whisky is distilled in it. Water pipes are made of it.
There is a good chance that you will survive the experience.
Just don't eat the kettle.

geoff smith
Geoff Smith
Hampshire, England

February 26, 2017

Q. Can you use a non stick pan which is over sized to boil down maple sap?

George Dlugolonski
- Levittown, New York

February 2017

A. Hi George. I see no reason you couldn't. But the reduction is usually something like 40:1, which is probably why large pans and even continuous operation is often done. A non-stick pan holding 2 quarts of sap would reduce to about one jigger of syrup. I'd probably drink at least 3 jiggers of bourbon while waiting for the maple flavoring :-)


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

March 2, 2018

Q. I have a rather large cast iron cauldron that I have been using to boil maple syrup. It is about 3 feet in diameter and 2.5 feet deep. I left a water vinegar mixture in the pot ( by mistake ) for about 8 months. When I emptied it, scrubbed and rinsed with water it appeared to be okay. However when I filled it with sap and began a boil it smelled absolutely terrible with a definite stale vinegar like odor.

Have I ruined my cast iron pot or is there a method I can follow to repair the pot so it is safe to use? I'm concerned that the cast iron and the acetic acid in the vinegar have reacted and permanently damaged the pot for use in making maple syrup.

Frank Solinger
- Owen Sound, Ontario, Canada

March 11, 2018

Q. Let me rephrase the description of the smell I'm getting from the cast iron cauldron when boiling even straight water in it ... it has a very strong cat urine smell coming out of the cauldron once you get up to boiling temperature. I spent hours with a drill and a wire brush cleaning the surface, followed by a good 10 hours of boiling water and baking soda, followed by straight water on the boil. Then rubbed a thin layer of vegetable oil into the cast iron surface and heated it up, repeating this process nearly 10 times to obtain a black coat on the boiling surface reminiscent to what you would have on your cast iron frying pan. Still have the cat urine smell coming out in the vapor when you boil straight water.

Frank Solinger [returning]
- Owen Sound, Ontario, Canada

March 15, 2018

A. Zinc coated, solid zinc, or galvanized steel should not be used on hot or cold syrup. The syrup has organic acids that dissolve zinc into the solution, and the flavor is ruined.

Bill Jackson
- Toronto, Ontario, Canada

March 19, 2018

Q. Sorry but I don't see how that response helps me out with my cast iron cauldron used for boiling sap. The cast iron cauldron I have was used by Mennonites for years and years before I got it. I used it last year with no problems. The smell issue came up this season after accidentally leaving vinegar in it for the whole summer and winter. I'm just trying to find out what can be done to get rid of the smell that occurs when the sap is getting boiled. It just started happening this year because of the vinegar.

Frank Solinger [returning]
- Owen Sound, Ontario

March 2018

A. Hi Frank. Bill was actually replying to Rodney's question from 13 years ago, echoed by Chris' from 11 years ago, and Richard's from 5 years ago. Patience please, someone will probably answer your question in 11-13 years, maybe even within 5 years :-)

Meanwhile, I think boiling baking soda in it for several hours as you did repeatedly was the best way to fix it. Since it didn't work, maybe try letting a citric acid solution sit in it for a day before boiling the baking soda again.

But one final thought: are you 110% sure that the smell is actually coming from the pot, not from the fact that you're heating the surroundings and filling them with warm condensate? We had a "cat urine" smell which seemed to wax & wane, but turned out to be a dead mouse in the wall. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

March 21, 2019

A. Frank Solinger ... I have an answer for your cast iron and a question for you.
You did not ruin the CI. Vinegar mixed with H2O is used in CI for cleaning up rust. It is usually followed up by a SMALL bit of soap and H2O and then rinsing with LOTS of H2O. The next step is to re-season it. There ale lots of methods but my most reliable method is to use a VERY LITTLE BIT of Crisco rubbed on to the cooking surface (and exterior) and heating the pot to about 500 degrees (the Crisco smokes at this point) then rub a very little bit more cCrisco on. Do this 5 or 6 times. It should darken with each coat until the cooking surface gets black.
The question is: have you made maple syrup in steel while your CI was out of commission? Did you notice any flavor differences?
Please let us know, Thank you!

Frank, I missed the part about 8 months with the vinegar. It could have etched the CI or leached into it. Generally they say 15-30 minutes soaking in vinegar. I would re-season and cook some bacon and or fatty meat/ soup in it a few times. That may complete the process and allow the remaining vinegar to escape. Just guessing now but Maybe a paste of baking soda on the cooking surface? Aaron Schlueter
Firefighter - Milford Ohio USA

March 25, 2019

Q. Hi, a similar question to the person trying to bring back their cast iron. I have recently discovered a large cast iron kettle in my possession and we are just trying to determine if there are any issues in using cast iron for boiling down maple syrup? Is it safe to use or should we be looking for a stainless steel vessel? This is just for home use for us too. Thanks

mike buhler
- New Melbourne, NL, CANADA
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October 19, 2019

Q. It seems that Copper conducts heat much better than anything. And, that is why copper is used in the bottoms of high-quality cookware because the metal rapidly conducts the heat and spreads it evenly across its surface.

Why would one use stainless steel instead ?

Grassa Brutta
- Melbourne, Victoria, Australia

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October 2019

A. Hi Grassa. You are completely correct about the better heat transfer ability of copper, but copper is not considered a food-safe material ... plus stainless steel is cheaper, more corrosion resistant, and easier to clean.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

November 15, 2019

A. Hi Grassa,
To elaborate on Ted's response, you'll notice that when copper is used for cookware, it is either sandwiched between layers of stainless (most cookware lines) or plated onto the outside (Revereware). When used as the primary material of the pans themselves (classic French and Portuguese cookware, which I absolutely ADORE), the food contact surface is coated with tin. When the tin layer is scratched or worn through, it has to be reapplied by a craftsman specializing in retinning, which is quite an art [ed. note: see threads 25553 and 29192]. But the protection from an inert layer is critical.
The only exception you will see is egg white whisking bowls which are raw copper. They are always scoured with lemon and salt immediately before use to remove oxides, and then rinsed. And all they are ever used for is fluffing up some egg whites to make souffles and meringues and such, where the contact time is very short, never for actually cooking.
I kinda want to make souffle now :)

Rachel Mackintosh
Plating Solutions Control Specialist /
Industrial Waste Water Treatment - Brattleboro, Vermont

November 15, 2019

thumbs up sign Hi Ted. Hi Rachel.

Many thanks to each of you for your responses.
The picture is now much clearer for me.

Thank you both.

Grassa Brutta [returning]
- Melbourne, Victoria, Australia

April 28, 2020

aff. link

Q. Dear Ms Rachel Macintosh,

I recently did some research over the web to establish the best method to melt chocolate or mix maple syrup with cocoa powder to make chocolate, and many looted that a Sugar Copper Pan such as a Mauviel Zabalione French pan for whisking egg whites.

My concerns are over the copper not being safe to heat in a Bain Marie the chocolate-making ingredients.
I have stopped using this method but was wondering how safe it was and and how does one know the after or side effects of copper oxidation in humans?



Many thanks,

Kris Sef
- London, UK

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May 1, 2020

A. Hi Kris,
The bare copper zabaglione pan is exactly what I use to make Ganache, and I've never seen evidence after use that the chocolate mix (cocoa, butter, cream- all fairly neutral pH, and short contact time) has reacted with the copper.

I can't speak to the safe contamination levels for ingesting copper so to give my very unscientific answer to the latter part of your inquiry, I have to quote the great Patsy Stone: "Not dead yet, sweetie darling!"

Also, I consume a lot of ganache. I expect to keel over of coronary failure long before the copper gets me.

Rachel Mackintosh
Plating Solutions Control Specialist /
Industrial Waste Water Treatment - Brattleboro, Vermont

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