Canning 101: Why You Can’t Cook Acidic Foods in Reactive Pots

September 29, 2010(updated on September 20, 2021)
Sterilizing jars

Whether you’re an expert canner, a beginner or someone who’s just contemplating dipping their toe into the home preservation waters, you’re certain to have heard that the only foods safe for water bath canning are the high acid ones. We define high acid as a food that’s got a pH of 4.6 or below (the lower the pH, the higher the acid content). The acid content of jams, preserved fruits, chutneys, pickles and more are our balm as canners, because it’s what keeps those preserves safe in their jars until you determine it’s time to crack them open.

There’s only one precaution that you must take when cooking these high acids foods into their canning-ready state. You’ve got to make sure you use a cooking vessel that is non-reactive. Pots made from metals like aluminum and untreated cast iron react with the acid in the preserves and can leach a metallic flavor into your final product. Shae at Hitchhiking to Heaven talks about an issue just like this in her most recent post in which she cooked high bush cranberries in a a cast iron skillet.

Note: The one exception here is when it comes to traditional copper preserving pans. Copper is a reactive metal, but when fruit and sugar are combined and cooked in a copper pan, the metallic flavor is not leached into the finished product. Once again, I refer you to Shae, and her post about copper pans.

Non-reactive pans are ones made of either stainless steel or enamel-lined cast iron (think Le Creuset or similarly enameled Dutch/French ovens). I recently acquired a low-and-wide 8 quart stainless steel All-Clad Stockpot that’s become my very favorite preserve-cooking pot. Its width means that the jam cooks down quickly and the stainless steel body allows me to scrub away when I accidentally let things overcook. We got it at Cookware & More, which is a kitchen wares outlet in Norristown, PA. They sell slightly irregular All-Clad products at a small discount, so if you’re in my area and in the market for some good cookware, you might want to consider checking them out (be warned though that it’s a strange store, tucked in the back of an anonymous industrial park in what feels like the middle of nowhere).

If you’ve got a stash of aluminum pots and want to give them some role in your canning process, you can always press the big ones into service as processing pots. The oval vessel you see in the picture at the top of this post is an old, aluminum pot I got in college at a thrift store. My mom and I have matching ones and we both find that it works nicely when we need to process a slew of half pint jars.

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74 thoughts on "Canning 101: Why You Can’t Cook Acidic Foods in Reactive Pots"

  • This is a bit creepy, boyfriend and I were having this EXACT conversation last night while standing over our Le Creuset, simmering some late Summer squash for pickling! He had a moment of panic when reading the recipe over again and seeing the ‘non-reactive’ bit, but I assured him that our Le Creuset was just fine…and now I have reinforcement!

  • So, I have what I believe to be an old aluminum pot that I’ve been using for cooking just about EVERYthing. It has a larger sibling that I generally use as the water bath pot. I haven’t noticed that any of my canned items taste metallic. Is it because a) it’s been used so much that it has built up a nice little cooked/burned on coating? b) that my palate isn’t as good as I think it is and they DO taste metallic? or c) I don’t really know what aluminum is. (I’m hoping for A.) Thanks for this post!!

  • Is it possible it’s anodized aluminum? anodized aluminum is made specially to not get into the food you are cooking, but I don’t know if it can stand up to high acid foods (although I thought that was the point).

    Marisa, do you know if all this good info is just on untreated normal aluminum pots, or is it pertinent to all aluminum pots, whether anodized or not?


    1. Mary, anodized aluminum is sort of a different animal and should be fine. I was only talking about those old school, untreated aluminum pots.

        1. My understanding is that at least one study did not find leaching of aluminum into food, if the cooking surface is anodized. In fairness, I don’t think it has been studied extensively.

          If you go out to eat, your food may well be cooked in aluminum, and generally not anodized aluminum. The heat transfer is very good, and the pans are cheap to buy. Commercial cookware gets ridden hard, and the restaurant is judged by serving food “just right”, so you can see the appeal of aluminum. Of course, what you eat every so often is less harmful than your daily diet.

    2. Anodized aluminum can still leach metallic flavor into food. I have Calphalon anodized aluminum pans and made the mistake of using one to make balsamic reduction. It tasted so metallic I had to throw it all out.

  • My fave pot to use is my husband’s IKEA 365 Stockpot. It’s 12″ in diameter, 7″ tall, and holds 11 quarts. I have been using it all summer long without issue and with lots of great results.

  • What about pots with nonstick coating? My set of pans is Pampered Chef, and they’re hard-anodized aluminum with nonstick coating. I’ve been using my enameled cast iron, but it would be nice to have more options!

  • i use an aluminum pot for processing, but i’ve found that i get a kind of chalky film on the outside of my jars when they dry. do you get the same from your aluminum pot?

  • Cat, I don’t like to use non-stick cookware for jam making, but I think that’s more personal preference than scientific fact.

    Maltese Parakeet, I get that chalky film in any processing pot. It’s the minerals in your water. I’ve found that adding vinegar to the water bath can help prevent it.

  • I get that chalky film too and first time thought I hadn’t cleaned out my mom’s canner well enough, but discovered that yes, it was due to our hard water. Thanks for the tip on adding vinegar to my canning water, I use it in my washing machine, but hadn’t thought to use it in my canner!

    1. I use vinegar in the canning pot and after clean with a cream of tarter paste to remove any residue

  • Marisa, thanks so much for the (double!) shout out. I think it’s great if folks can learn from my mistake with the iron-apple butter. As much as I’ve learned from investigating different kinds of metals for jam pans, I find that I still have some floating questions. One of them has to do with the cast iron:

    I wonder whether cast iron would behave the same as copper if the fruit were mixed with sugar before it is added to the pan. I cooked down raw cranberries in my cast iron pan (I know, I know) but I wonder what would have happened if they’d gone into the pan with the sugar. I bet the reaction would have been significantly less. Witness, for example, this gorgeous skillet jam offered by Dinner with Julie. I don’t think her cast iron skillet is coated, though it’s hard to tell for sure.

  • Shae, was actually thinking about Julie’s skillet jam while I was writing that post and wondered something similar. I also wonder if it also has to do with the fact that strawberries have less acid than cranberries. Maybe? It’s the sort of thing I’d be excited to do some semi-scientific tests on, if only I had the time.

  • Yes, I want to learn more about it, too. And I agree — there’s probably not much worse you could prep in a reactive pan than raw cranberries!

  • What about pots with nonstick coating? My set of pans is Pampered Chef, and they’re hard-anodized aluminum with nonstick coating. I’ve been using my enameled cast iron, but it would be nice to have more options.

  • For years (since the late ’70s) I’ve been using a combination of a 42 pint stainless and 42 pint aluminum stock pot for cooking my tomatoes for canning. I often need that much capacity for a canning session. Being too dumb to know that I should not use reactive metal to cook the tomatoes, I just did it. At times, I have also used enamel lined pots and even my electric roaster. I have never noticed a difference between them in terms taste or quality of the finished product. In fact, I enjoyed some 2011 vintage juice this morning for breakfast…yummm!

  • I found a pizza tray I thought would be ok so I tossed it into a large pot to keep jars off bottom. I first, sterilized the jars then boiled the filled jars in the same water. I used a separate non-reactive pot for the brine.
    Did I destroy the pickles?
    Do I need to throw away all of it or are they still edible? They’ve been in the cabinet since I made them because I noticed the pizza tray totally oxidized while boiling. Duh! 🙁

    1. Your pickles are fine. You only want to avoid reactive cookware when you’re cooking the food. Once it’s in the jar, it won’t impact the quality of the finished product.

  • What type of pots are the magnalite?Cant find the answer on the net. That’ for fs what I use for beets and pickles.

    1. If it’s the dark grey thick metal (vs much thinner typical stainless, copper or aluminum pots), it’s probably anodized aluminum. My magnalite skillet (heavy pan) is anodized aluminum.

  • What about ladles?

    My Mom has a vintage Wagner Ware aluminum ladle that is the perfect shape for pouring the jam into the jars. Will that little bit of exposure react with the jam or leave a metallic taste?

  • I made 16 quarts of apple sauce in a stainless steel pot which turned out great! Tonight I made another batch using the same batch of apples, however this time I used an anodized aluminum pot. The end result was significantly different. It had a distinctive taste that until this blog, I could not place. Now it is clear that it is a metallic taste. I wonder now if it should be dumped.

  • I always do all my canning with stain steel surface because from what i read, it seems to good as it is non reactive with most food items.

  • What about the really old enamel ware pans/pots? Mine are the white ones with the red trim around the rims. Some have chips on the outside but not the inside. Are these ok to cook my pickle brine in? I don’t have another really large pan? Just getting started. Only use these normally for my kitchen decorations only, have them hanging in my antique looking red & white kitchen???? Thanks, Cindy

  • It is being studied now that aluminum from soda and Beer cans might cause Alzheimer’s and maybe add in children. Might explain my problems

  • Darn!!
    I just happened to read this after my fist ever canning in which I made and canned 8 pounds of tomato relish… better eat it now.
    I suppose it wont last long at all.

  • I have made some elderflower cordial and left it to cool in a stainless steel pan
    When I came to decant it after an hour the cordial had reacted with the metal and turned it black ?
    Is the cordial still drinkable as it does not taste metallic
    Is it now poisonous ?
    Thank you

    1. Stainless steel isn’t a reactive metal, so it probably oxidized because of the air exposure. As long as it tastes okay, it is safe to drink.

  • I make refrigerator pickles, I’ve never processed them for proper “canning” but for the past 2 summers, I’ve been tweaking my process and I find that my brine always comes out better when cooked in one of those old fashioned blue-with-white-specks enamel pots.

    My aluminum pots caused strange flavors consistently, particularly if I used less salt. Also noticed that the pickles were much crisper.

    1. Aluminum is always going to cause strange flavors because it’s a reactive metal and so is imparting that metallic flavor into your brine.

  • question about aluminum sheet pans (still a canning question, i promise). i’m about to do a batch of tomato paste, and would love to cook down the paste on my sheet pans, since they’re deeper than the other pans i have. but the pans are aluminum, and i cannot determine if it’s anodized. should i just deal with my barely deep enough jelly roll pans, or are the sheet pans safe, do you think? thanks!

  • Oh boy! Two questions. I canned about 16 1/2 pints of strawberry preserves about a week ago. My 2nd batch, as the first batch batch was made for family to refrigerate and eat. This last batch was to put up for the ear in the pantry. Not knowing I used a nonstick black lined pot! Do I need to throw them all away? Second question. I bought a stainless steelpots now that I know better. Do I need to season them? If so, how?.

    1. The jam should be fine. In the case of non-stick, the jam making process can be hard on the non-stick coating, causing it to be less non-stick over time. And you don’t need to season stainless steel. Just give it a good washing the first time out and you’re ready to go.

  • I recently made pickles that have to soak in lime for 24 hr. I was not thinking and put them in my mothers old aluminum pot. When i took them out the bottom of the pot was etched and turned white after it was washed. I finished them in a stainless steel pot. Are they ok?

    1. The pickles might have a metallic flavor after contact with the aluminum. You should taste them to see.

  • So the pots and pans that I have are a bit older and I think it might be time to replace them. As you said here, there are some things that I have to look out for as certain materials will react with others in a negative way. I’ll probably see about going with some stainless ones as there is pretty much no chance that they’ll react negatively.

  • I just canned 14 jars of tomatoes and 5 jars of salsa for the year. I cooked the tomatoes in an older aluminum pot. Are the tomatoes safe to eat or should I discard?

  • I am going to process tomatoes. I have a pot big enough for the blanching stage that is stainless. I plan to do quart sized jars and the only pot I have that is big enough for the water bath stage is aluminum. Is that ok?

  • I recently bought a large deep alluminum pot to use as hot water bath for dill pickles. The inside of the pot turned black. Should I throw out 20 quarts of pickles?

    1. Your pickles should be fine. The food you’re canning doesn’t come into contact with the water from the canner, so any reaction that occurred shouldn’t impact your product.

  • I was given a copper jam pan a few years ago as I love making various jams, many of which involve stirring the fruit with pectin & lemon juice & adding sugar in once the fruit is boiling (peach, strawberry). It’s unlined and I’m just now hearing I shouldn’t be putting any fruit in there without it being mixed with sugar first.

    Do I need to dump all of the jars I have where the pectin/sugar method was used? I’ve never noticed an off flavor & our family has gone through dozens of jars.

    Thanks for any insight!

  • I have been looking for a stainless steel ladle. I am currently using a stainless steel measuring cup. I test my equipment using a magnet – if the magnet adheres to the pot, etc. then it is stainless steel. However, I just purchased an 18/8 stainless steel ladle and did the magnet test. The magnet does not adhere to the ladle. My question: is 18/8 stainless steel good enough not to react when canning?

    1. As long as it isn’t aluminum, it should be fine. Your food only spends a short time in contact with the ladle, so there’s little time for any acidic leaching.

  • I have a double batch of bread and butter pickles that I doubt will fit in my stainless steel tock pot. Can I prepare them in one of my black hot-water bath canners? Thanks!

    1. I would only use a canner for an acidic food like pickles if it can be scrubbed clean and doesn’t have any dings or cracks in the enamel. If there are any flaws in the enamel, you can potentially impart a metallic flavor into the food from the bare aluminum of the pot.

  • My pot for cooking lemon preserves is all clad with an copper core. Just need confirmation that this pot would be good to use

    1. Yes, that’s a great pot. It’s got a stainless steel interior, which is always a good choice for acidic foods.

  • I just made 4 pints of pickles (my first time canning.) Without really thinking I made the brine in a non enamel coated cast iron pot. Do you think they are going to have an iron taste? I’m so bummed that I didn’t think about that.

    1. They very well may have a metallic flavor. It depends a lot on the quality of your seasoning on the pot.

  • What about Copper Chef pans? They have a non-stick coating. I just made my first pickles ever and now I’m freaked out that I need to toss them! I have 12 jars of pickles / pickled okra made in this!

  • I was cleaning out my freezer and found sliced apples and peaches which I threw into one of my canners to cook down for apple/peach butter I haven’t added anything else. Will the aluminum kill me or is it just an off putting taste?

    1. It’s not going to kill you, it just may impart a metallic taste to the finished product. If it tastes okay to you, it is fine.