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5 from 2 votes

Fermented Onions Recipe

Subdue the pungent taste of raw onion and add a subtle sweet note by lacto-fermenting onions. Fermentation makes raw onions more palatable, while reserving and enhancing the health benefits. Onions, red onions in particular, are a high source of quercetin, a flavonol plant compound, with anti-inflammatory, antioxidant, antihistamine, antiviral, and cardio- and neuroprotective properties. Fermentation boosts the power of quercertin, so it can work better in your body.
Prep Time10 mins
Cook Time0 mins
Fermentation time28 d
Course: Side Dish


  • 1.5 L Airlock Fermenter, knife, cutting board, (mandoline, optional)


  • 5-6 organic red onions, peeled and sliced (reserve the peel)
  • 600 mL non-chlorinated, filtered water
  • 12 grams non-iodized sea salt (about 3/4 tablespoon fine-grain salt)


  • Make a 2% brine: dissolve the salt in hot water; set aside to cool.
  • Wash onions to remove any dirt from the papery onion peel; remove and reserve. Cut any other papery area of the next outer layer underneath the peel; reserve. Half the remaining onion from tip (scape) to root. Slice onions crosswise, about 3-5 mm thick. Determine the thickness of your slices depending on how you intend to use these onions after fermentation (i.e. on hamburgers or tacos, in soups or stews). Alternatively, chop the onions in whatever shape lends well to recipes that call for onions.
  • Place the reserved onion peels into the bottom of a clean 1.5 L Airlock Fermenter. Layer the sliced onions over top, gently packing them with a clean fist or fermentation tamper. Pack jar with onions half an inch below the shoulder. Place a flat glass weight on top. Pour brine overtop to the neck of the jar or until it covers the glass weight by half an inch. (You may have brine left over.)
  • Fill the large airlock with water to the fill line, and insert through the lid. Latch lid and clamp shut. Store at room temperature, between 18-21ºC, out of direct sunlight for 7 days days, then transfer to a fridge or cold storage (<12ºC) for 3 weeks. Will keep for 1 year in an unopened Airlock Fermenter.
  • When ready to eat, replace airlock with the plug. Refridgerate after opening. Ensure onions stay submerged under brine. Discard the onion peels once the onions are consumed. Use within 3-6 months.