Canning Onion Confit

There are some spectacular onion confits and jams floating around the internets right now. This one is an onion and rosemary confiturra from Serious Eats, via The Kitchn, that I heard about through a round-up post on Consider the Pantry (got that?). It’s a luscious combination of red onions, balsamic vinegar, red wine vinegar, white wine, honey, sugar, and herbs. The recipe is perfect—I didn’t change a thing—but I do want to say a word about preservation. Serious Eats says that this is fine for water-bath canning. I’m not convinced.

Here’s my logic. Onions are a low-acid food. To make them safe for water-bath canning, you have to add sufficient vinegar to drive the pH below 4.6. The question is whether there is enough vinegar in this recipe. If you have pH strips handy, then you could just find out, and proceed accordingly. If you don’t, however, you have to do some sleuthing.

Two things made me nervous. First, while Joy of Cooking includes a similar recipe for what they call “red onion marmalade,” it’s not included in their list of condiments safe for canning. But it was what I found in the Ball Blue Book that really convinced me. The Blue Book includes two different recipes for preserved onions: one for water-bath canning, and one for pressure canning. Their red onion marmalade, safe for water-bath canning, has a ratio of 1 1/2 c. onions to 1/4 c. vinegar, plus some orange peel and a whole lot (4 cups!) of sugar. The red onions with honey recipe, on the other hand, has 2 1/2 quarts onions, 1/2 c. wine, and 1 c. honey, and must be pressure cooked. Serious Eats’ confiturra has about 10 cups of onions, 3/4 c. vinegar, and 1/2 c. wine, but by the Blue Book logic, you would need 1 2/3 c. vinegar for 10 cups of onions. Given that the Blue Book is known to be conservative, it strikes me as within the realm of the possible for 3/4 c. of vinegar to be enough, but since I’m giving these as gifts, I wanted to play it safe. Fortunately, since this is a heavily cooked product anyway, there’s no harm in pressure canning the jars.

All of which is a long way of saying: if you want to preserve a low- to moderate-acid onion confit, pressure can the jars at 10 pounds for 15 minutes. If you don’t have a pressure canner, they’ll keep in the refrigerator for at least a month. As a reminder, I’ve got step-by-step pressure canning instructions here.

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14 comments to Canning Onion Confit

  • MK

    I think it would are right….see this paper:

    It says that a pint of onions is properly acidified with 60 ml lemon juice, and vinegar would be the same pH as that. The recipe calls for 1/4 c. red wine vinegar, which is 60 ml. But it has a 1.5 pints total of product.

  • I appreciate all the logic on waterbath vs pressure. I’ve thought about getting pH strips so that I could test out new recipes and know whether they were safe to water bath can. Have you tested pH for canning purposes before?

  • dorisandjilly

    MK: Do you think that means a pint of onions BEFORE cooking, or after? Raw, this used about 2 1/2 quarts onions, so I’m still not sure. Emily: I haven’t actually tested for pH before, because I tend to either follow directions or make up things based on other recipes. Next spring, though, I think I’ll buy some so I can experiment with salsas. You should be able to find them at hardware stores and some pharmacies.

  • Kim

    Looks so good! I’ll have to try this one.

  • Red onion marmalade. The Joy of Cooking recipe is delish. Thanks for wrapping your head around the technical points!

  • I have pH strips but they’ve let me down cheesemaking before so I’m nervous about using them for canning. I wanted to can carmelized onions last fall and looked into this as well. I finally decided to just freeze them in ice cube trays since my favorite onion recipe has some cream in it and you certainly couldn’t can that, at least I don’t think.

    I’m thinking about getting this:

    Anybody else out there have a reader?

  • onion confit sounds interesting . . . what would you do with it?

  • dorisandjilly

    It’s very nice with meat (esp. pork), or with cheese on a cracker. You could probably use it in all sorts of interesting cocktail snacks.

  • Regarding BWB canning, I tend to agree, Doris: I don’t think this recipe is safe for water bath canning. Here is a link to the full paper referenced by MK above:

    Now, I think the conclusions are conservative; based upon the data, 15 mL of lemon juice safely acidified 100 grams of onions to a pH of 4.0. But the final conclusion is that 30 mL of lemon juice/100g onions is required (for a pH of around 3.4). Then they go on to say that 60 mL (or 1/4 cup) lemon juice safely acidified (pH of 3.6 – 3.8) a full pint (~2 cups) of packed, raw, onions (weighing no more than 300 grams, or 20 mL lemon juice/100 grams onions).

    It took a greater amount of vinegar (3/8 cup) to equal the pH (3.8) of 1/4 cup lemon or lime juice in a tomato/onion/pepper salsa test. However, 1/4 cup of vinegar was still safe, at pH of 4.2 (but there were tomatoes in this test, so I can’t rely on these data for onions alone).

    So, my inner geek suggests: 1/4 cup of lemon juice is quite safe for 2 cups packed, raw onions. This translates to 3/8 cup of vinegar for 2 cups packed, raw onions. So 10 cups packed, raw onions would need 15/8 cups (oh, math!) or close to 2 cups vinegar. Given the addition of 1/2 cup olive oil, I would think you’d need even more vinegar to balance that out.

    What’s difficult to tell in the recipe is whether or not you could cook the onions down, and the *resulting* 2 cups onions would be safely acidified with 3/8 cups vinegar (or 1/4 cup lemon juice). The paper says that they packed raw onions into pint jars, added 1/4 cup lemom juice then “cooked, repacked into hot jars, and processed.” No mention of how much volume they lost in cooking.

    I SO need a home pH meter. If only I’d known, back in my laboratory days, that I’d become a rabid home-canner, I would have ‘borrowed’ one from the lab for my kitchen experiments!

  • This is a VERY informative thread. I just made Roasted Garlic and Caramelized Onion Jam for Christmas gifts (recipe in Amendt, L. J. 175 Best Jams etc.), water bath canned the jars – as per the recipe, and then, after labelling them to be used in 3 months, found, to my horror that the recipe calls for the jars (post-water bath canning) to be stored in the fridge. I just emailed the lucky recipients to advise them about this!! I was wondering about the necessity of fridge storage for the sealed jars – I think that the author is being very conservative.

    Having said that, I am still very concerned: The recipe is 5 cups onions, 4 bulbs roasted, squeezed garlic (about 0.5 cup total), 0.5 cups balsamic vinegar, 1 cup cider vinegar and 3 cups sugar. Seemingly, this falls within the Ball Canning book ratio (1.5 cups onion to 0.25 cups vinegar to 4 cups sugar) and should be able to be stored out of the fridge.

    However, given the thread I have just read here, clearly, there needs to be some testing of pH. I have noted from the Bernadin canning book (the Ball equivalent in Canada), that pH must reach 4.6 acidity. So, I guess that the only way to be certain about safety of water canning is to test the pH. Best way to do that, if you don’t have access to a pH meter in a biology lab (I am a biology professor), is to ask your friends who are in Biology undergraduate classes to bring home some unused pH paper strips from their labs – these are usually bought each year. You only need a couple inches of the paper.

    I am also going to ask a question about this on Linda Amendt’s website.

  • Sally Dillon

    I hae a garden full of onions and I am looking for good canning recipes! I amstill not clear on all this – as I have just started canning. I have both a hot bath canner and a pressure canner, but I have not used the pressure canner as yet – it is a but intimidating! Want to try to can carmelized onions as gifts. I am having a terrible time finding a recipe! I made some onion jelly last year in the hot bath canner – I dont think it is very good though – the col;or is not appetizing. I wonder if it is even safe! It’s sitting in my pantry! Any info anyone can share is greatly appreciated!

  • I am inspired by the conversation. I happened upon this post because last night I had a dream about making an onion-apple-strawberry jam and went hunting for recipes. The recipe I made today was an adaptation of Homegrown Pure and Simple by Michel Nischan, and it said to process in a boiling water bath for 20 minutes. I’ll report back if they spoil (although the jars may not last that long. It was delicious!)

    Keep canning!

  • Diane

    Question – what about freezing confiturra? Any insights?

  • Kim

    I’ve made the Serious Eats recipe and it freezes wonderfully – I use the 8 oz. Ball freezer jars.