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Tangy fermented red onion slices

These fermented red onions are crisp, vivid and gently tangy, made in a simple 2% salt brine. Their bright colour and lively flavour make them a beautiful, practical topping for sandwiches, tacos, grain bowls, salads and everyday meals.

July 13, 2026

Brine and Bloom

Writing about fermentation for healthier living

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These fermented red onions are bright, crisp and gently tangy, with a vivid pink colour that deepens as they ferment. Easy to prepare and highly versatile, they are perfect for sandwiches, grain bowls, salads, tacos, burgers and summer plates.

FAQs

How long do fermented red onions take?

They usually take 3–7 days at room temperature, depending on the temperature of your kitchen and how tangy you want them. Taste from day 3 and move them to the fridge when they taste right to you.

Why are my onions turning bright pink?

That is completely normal. Red onions release their pigments into the brine during fermentation, creating a vivid pink or magenta colour that is one of the most appealing parts of this ferment.

How can I use fermented red onions?

They are excellent in sandwiches, wraps, grain bowls, burgers, tacos, salads and mezze-style plates. They also pair very well with roasted vegetables, cheese, beans and grilled halloumi.

Lacto-fermented red onions

Ingredients:

Makes 1 medium jar

2 medium red onions, about 300–350 g
10 g fine sea salt
500 ml filtered water
1 garlic clove, lightly crushed, optional
½ tsp black peppercorns, optional
½ tsp mustard seeds, optional
1 small bay leaf, optional

Directions:

Dissolve the salt in the filtered water to make a 2% brine. Stir until fully dissolved.
Peel the red onions and slice them into thin half-moons or rings, depending on your preference.
Place the garlic, peppercorns, mustard seeds and bay leaf, if using, at the bottom of a clean jar.
Pack the sliced onions into the jar, pressing them down gently but firmly.
Pour the brine over the onions until they are fully submerged. Leave about 2–3 cm of headspace at the top of the jar.
Use a fermentation weight or a small food-safe weight to keep the onions below the brine.
Close the jar loosely, or use a fermentation lid. Leave at room temperature, away from direct sunlight, for 3–7 days.
If using a standard lid, open the jar once a day to release gas. Press the onions down if needed to keep them submerged.
Start tasting after day 3. When the onions are lightly tangy, slightly softened but still crisp, transfer the jar to the fridge.
Keep refrigerated and use clean utensils when serving.