Fermented Onions

How to make salt-brine fermented onions

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Fermented onions are crisp and crunchy pickled onions. The mild flavor is perfect for anyone sensitive to raw onions. They are delicious with grilled cheese or sliced into salads. 


Units Scale
  • 3 cups small cocktail onions or 2 large onions, sliced
  • 1 Tbsp non-iodized salt
  • 1 to 2 1/2 cups water (chlorine-free)
  • 1/4 cup culture (optional – see section above for details)


  1. Prepare the onions by slicing off the ends and peeling them. Pearl onions are easier to peel if they are submerged in cold water for about 10 minutes. Do not blanch them, as you don’t want to kill the natural bacterial culture on the onion. Large onions can be halved and sliced into thin rings.
  2. Mix the salt and 1 cup of water in a quart-sized (1 L) jar to make a brine. Mix in the culture, if you are using one. Onions don’t need a starter culture, however, it is a nice way to add flavor. See the section above for details.
  3. Add the onions to the jar and top with a weight. Onions float, so it’s important to use a weight to keep them submerged in the brine. Add enough additional water to fully submerge the onions. The exact amount required will depend on whether you’re using pearl onions or sliced onions, and if you’re using a starter.
  4. Cap with a loose-fitting lid or a fermentation-specific lid. Leave the onions somewhere dark to ferment for up to 1 week. They can be left in a dark location for up to a year, however, you need to take extra care to ensure a good ferment. See the notes for details.
  5. After fermenting, store in the fridge and use within 1-2 months.


  • If you are sensitive to raw onions, make fermented slices rather than whole pearl onions, as they will be easier to digest.
  • To ensure a good long ferment (more than one week), make sure to sanitize your jar. It’s also important to use a fermentation-specific jar that will allow gas to escape while preventing contamination. Personally, I like fido jars.
  • It’s okay if you don’t have a good fitting fermentation weight. Just be sure to stir your onions every two days, so that all onions have a chance to be below the brine.