Fermented onions are mildly tangy, naturally sweet, and packed with probiotics that support gut health. This simple ferment transforms ordinary onions into a flavorful condiment that’s perfect for topping salads, sandwiches, or adding brightness to cooked meals. Their gentle acidity and crunch make them an instant kitchen favorite.
Ingredients (for a 1L Fermentation Jar)
- 650 g onions, thinly sliced
- 20 g sea salt (1 tbsp)
- 300 ml filtered water (1½ cups)
Step-by-Step Recipe
Instructions
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Prepare the Onions
Peel and slice the onions thinly. In a bowl, mix the onion slices with sea salt and let them rest for 1 hour. Massage gently to help release their natural water. -
Sterilize the Jar
Clean your 1L fermentation jar with hot water and let it air dry completely before use. -
Pack and Add Brine
Transfer the onions along with the water they’ve released into the jar, packing them tightly to remove air pockets. Place a glass weight on top to keep the onions submerged. Pour in the filtered water to cover the onions completely. Leave at least 2 inches of headspace in the jar to allow gases to expand during fermentation. -
Seal with an Airlock
Close the jar with a grommet lid. Fill the airlock halfway with water so gases can escape while keeping contaminants out. -
Ferment
Let the jar sit at room temperature (around 25–30°C / 77–86°F) for 5–7 days. -
Check Daily
Press down gently each day to ensure the onions remain submerged. Begin tasting from Day 5 — they should develop a light sourness with a pleasant crunch. -
Store and Enjoy
Once the flavor is to your liking, remove the glass weight and airlock, seal with a storage lid, and refrigerate. These fermented onions will keep well for up to 6 months.
Tips & Notes
- Salt Ratio: 3% brine keeps onions crisp and safe for fermentation.
- Headspace: Maintain 2 inches to avoid overflowing brine.
- Airlock Lid: Reduces the need to open the jar during fermentation.
- Flavor Boost: Add chili flakes, black pepper, or thyme for a spiced variation.
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Storage: Keep refrigerated after fermentation; flavor deepens over time.
Final Thoughts
Fermented onions are the perfect mix of tangy and sweet — a probiotic condiment that elevates any meal. Try them in sandwiches, tacos, or grain bowls for an instant flavor upgrade!
