Canning Onions (and French Onion Soup)

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Canning onions in a pressure canner is an approved preservation method, but there’s a specific technique to follow.  Learn how to can plain onions, without pickling, and how to modify the recipe for canning french onion soup in beef stock.

Honestly, I’d never really thought about canning onions, it just didn’t seem necessary.  We usually grow storage onion varieties that’ll easily keep 6 to 8 months in our basement, ensuring a supply until the following year.

The thing is, onions need to be cured properly before storage so they’ll develop a protective papery husk, and dry out their wet stem that’s liable to mold otherwise.   They’re harvested large, so there’s still plenty of onion left after the curing process dried out the outer layers.

What happens to small, bruised, or otherwise imperfect onions?  They’re usually used up early rather than stored, as there usually aren’t all that many.

This year, my overzealous 5-year-old garden helper decided to harvest several hundred onions a few months early.  Right in the middle of the summer, I’d sent her out to grab a few fresh onions for dinner…she got a bit carried away, harvesting whole beds and leaving them laying there on the soil until she found the perfect one.

About 20 minutes later she came back in, carrying dinner onions.  I didn’t notice the rest of the dug up onions until they’d lain there in the sun for several days, long past re-planting, and definitely in no shape for curing.

It was way more than we could possibly use before they spoiled, and I wasn’t about to sacrifice the freezer space that we desperately needed to store sweet summer berries.

Time to learn how to can onions!

There are actually a few reasons to can onions, beyond the depredations of an overzealous kindergartener.

Not everyone has a cool basement storage location, especially people living out west where basements don’t really exist and it’s hot much of the year (indoors and out).  In that case, sauteeing them then packing them into the freezer is a good second choice. 

That assuming you have a lot of extra freezer space, but really that’s best used for storing meat or a summer’s worth of frozen berries.  Canning provides you a good option without taking up freezer space.

Even if you never attempt to can onions, knowing that you can is important.  Why? 

The national center for food preservation put out a “choose your own adventure” pressure canner soup recipe, that allows you to make up your own recipe and safely can it.

The only caveat is that all the ingredients must be safe for canning individually.  You can’t add eggs, flour, or pasta to the soup, but since there is a safe canning recipe for onions, you’re able to add those if you wish.

In theory, since there is a canning recipe for onions, you could use that same “choose your own adventure” soup canning instructions to can just onions alone in a jar (with beef stock, veggie stock or water).  I’ll walk you through that option at the end, after discussing the specific tested recipe for pressure canning onions.

(If you’re not familiar with pressure canning, I’d recommend you read this beginner’s guide to pressure canning before you get started.)

How to Can Onions

The instructions for canning onions are rather specific, not necessarily because this is the only possible method, but simply because it’s the only “tested” method.

In the US, safe canning recipes are determined by the national center for food preservation in coordination with agricultural extensions.  They only have so many resources, and they can’t test every possible permutation.  The cooperative extension at Clemson College tested a recipe for canning whole small onions, about 1 inch in diameter.

“Onions are low acid foods with a pH of 5.3 to 5.85. Thus, if they are to be canned, they must be pressure canned for safety. This tested recipe is specific for onions of 1-inch diameter or less…

• Wash and peel onions.
• Cover with boiling water, bring to a boil, and boil for 5 minutes.
• Pack onions into hot jars, leaving 1-inch headspace.
• Add ½ teaspoon salt to pints or 1 teaspoon to quarts, if desired.
• Fill jar to within 1 inch from top with boiling water.
• Remove air bubbles leaving 1-inch headspace. Wipe jar rims and adjust lids to fingertip tight.
• Process pints or quarts in a pressure canner for 40 minutes. At altitudes of 0 to 2,000 feet, process jars at 11 pounds pressure in a dial gauge canner; in a weighted gauge canner, process jars at 10 pounds pressure at altitudes of 0 to 1,000 feet and at 15 pounds pressure for altitudes above 1,000 feet.”

This is the process I’m going to test with my small onions, mostly to see how they turn out. 

After the onions are peeled, they’re then boiled for 5 minutes and then packed into jars leaving 1-inch headspace.  They’re then pressure canned for 40 minutes, with a pressure adjusted to altitude (see above).

I wanted to see how they’d change in the canner, so I filled two jars with onions that had been boiled 5 minutes as described.  I canned just one of them (the quart pictured below) and left the second jar alone without actually canning it.

As you can see, the onions that I canned browned considerably in the canner as the sugars in their tissues caramelized.  I was actually pretty pleased by this because I hoped to be able to use them as a french onion soup base later and caramelization is ideal.

(You can also see that the jar siphoned a bit, losing liquid.  That’s fine and just a cosmetic issue, not something that impacts canning safety so long as the jar is sealed.)

Using Home Canned Onions

So now that I have a jar of home-canned onions, I wanted to see how they’d taste.

They’re quite soft, as you’d imagine after 40 minutes in a pressure canner.  They’re a lot like onions that have been in a slow cooker with a pot roast all day.  Flavorful, slightly sweet, and onion-y of course.

I pulled them out of the jar and chopped them up to make french onion soup, mixing the jar liquid with a jar of home-canned beef stock as the base.  

Canning French Onion Soup

The result was totally fine, but would have been better, in my opinion, if they’d been canned in the beef stock from the beginning.  Thus canning french onion soup instead of just canning plain onions.

That actually is an option, with the “choose your own adventure” canning recipe.  With that recipe, you prepare the vegetables for hot packing, and then pack the jars half full.  This recipe relies on the fact that the jars are only half full of solids, and are mostly full of stock/broth/water so that heat can fully penetrate the soup during canning.   

Top with boiling water or stock, leaving 1-inch headspace, and then process according to the table below.

So now you’re thinking, is a half-full jar of french onion soup really the right ratio?  I found it worked out really well, and it ensures that there’s enough rich flavorful beef stock in the jar to fill the bowl and absorb into the croutons at the top holding up a thick slice of gruyere on a traditional bowl of french onion soup.

I did chop the onions for this soup, rather than leaving them as whole pearl onions as in the onion canning recipe.  That saves work at serving, and the longer canning time and half-filled jars ensures that heat fully penetrates the jars.

(Chopped onions are in other tested safe canning recipes, like canning beef stew, for example.)

What I wouldn’t do, is sautee the onions first.  Onions really change when you sautee them for the 40-60 minutes it takes to slowly carmelize them for french onion soup, and they pack much more densely. 

I found that they really packed into a thick mass at the bottom of the canning jars, and that made me think of canning pumpkin.  You can’t can pumpkin puree because it’s just too thick for heat penetration, and you have to can pumpkin cubes instead.

I’d use that same logic when canning french onion soup, and just hot pack onions that have been simmered for 5 minutes in stock rather than sauteed onions.  

Inside the pressure canner the onions carmelize anyway, giving a rich flavor to the home-canned french onion soup.  I honestly didn’t miss all that time spent slowly sauteing onions for an hour on the stove, and I had a read made meal in a jar!

That’s my interpretation of the National Center for Food Preservation’s guidance, and that’s what I’m now doing in my house.  Obviously, I’d recommend you do your own research and make your own decisions when canning at home.

Here are some good resources:

• Clemson University Guidance on Canning Onions
• National Center for Food Preservation “Can Any Soup” Recipe
• National Center for Food Preservation Soup Canning Fact Sheet

Pressure Canning Recipes

Need a few more recipes to keep your pressure canner running this season?

• Canning Potatoes
• Canning Carrots
• Canning Pumpkin
• Canning Sweet Potatoes
• Canning Beets