Home / Fermentations

Fermented red onions

Fermented red onions are sharp, colourful, and incredibly useful. Their natural sweetness balances beautifully with the acidity of fermentation, creating a bright topping for sandwiches, bowls, eggs, salads, beans, and grilled dishes.

June 23, 2026

Brine and Bloom

Writing about fermentation for healthier living

Share this article:

Sharp, bright, and useful in almost everything

Fermented red onions are one of the most practical fridge ferments. They add acidity, colour, and crunch to sandwiches, tacos, eggs, beans, salads, and grilled vegetables.

Fermented red onions

Ingredients:

400g red onions, thinly sliced
400ml filtered water
12g fine sea salt
1 garlic clove, optional
½ tsp coriander seeds
½ tsp black peppercorns
1 small bay leaf

Directions:

Dissolve the salt in the water to make a 3% brine.
Place the coriander seeds, peppercorns, bay leaf, and garlic if using into a clean jar.
Add the sliced onions and press down lightly.
Pour over the brine until the onions are fully covered. Add a fermentation weight.
Cover loosely or use an airlock lid. Ferment at room temperature for 4–7 days.
The onions are ready when they are bright, tangy, and slightly softened. Refrigerate once ready.

Notes:

Use clean jars and utensils, keep vegetables fully submerged, and taste as the ferment develops. If a ferment smells unpleasant, develops visible mould, or feels slimy in an unusual way, discard it.

For beginner vegetable ferments, a 2–3% salt brine is a practical starting range, depending on the ingredient and method.