Black Olives in Brine, Naturally Fermented
The oldest and most patient method: ripe black olives go into salted water uncut and give up their bitterness on their own over several months.
- Time
- 3-6 months
- Serves
- 3 kg
- Level
- Medium
- Cuisine
- Mediterranean
This is the oldest form of olive curing: no intervention at all, the fruit neither cut nor cracked. The olives go into salted water and time passes.
The work is done by lactic acid bacteria. Able to multiply in a saline environment, they convert the sugars in the olive into lactic acid; the acidic conditions that result both suppress spoilage organisms and help break down oleuropein, the bitter compound. So the bitterness here is not simply washed out — fermentation is working too.
In return it asks for patience: three to six months, depending on variety, ripeness and temperature. What you get is a depth the fast methods cannot produce. For a comparison of the methods: how olives are cured.
Directions
- Sort the olives: choose purple-black fruit that is fully ripe but not yet soft, discarding any bruised or rotten.
- Rinse and drain them; they do not need to be fully dried.
- Make the starting brine: dissolve 240 g of rock salt in 4 litres of water (6%).
- Put the olives in a large glass or food-grade plastic container and pour the brine over to cover.
- Hold them under with a plate and a clean weight — any olive that floats will go mouldy.
- Cover the container with cloth or a loose lid. Fermentation produces gas, and a tightly sealed container builds pressure.
- Through the first month, check the surface weekly and lift off any foam or white film with a clean spoon.
- At the start of the second month, refresh the brine: pour off the old and make a new one at 8% (80 g salt per litre).
- From the third month, taste monthly. The olives are ready when the bitterness has gone — three to six months depending on variety.
- When ready, pack into jars with the thyme and lemon, top up with brine and float a finger's depth of olive oil on top.
Tips & storage
⚠ Never seal the container tightly. Fermentation produces carbon dioxide, and a tightly closed glass jar can crack under pressure. Use a cloth cover, a loose lid or an airlock.
Too little salt and it spoils; too much and fermentation stops. Six per cent is right at the start: it lets the lactic acid bacteria work while suppressing what you don't want. Raising it to 8% in the second month secures it for storage.
A white film is not cause for panic. The thin white layer on the surface is usually harmless kahm yeast and is lifted off with a spoon. But if you see fuzzy green, black or pink mould, that batch is discarded.
The olives must always stay under the brine. This is the most common cause of spoilage. A sealed bag filled with brine makes a good weight.
Warmth speeds it up and raises the risk. 18–22 °C is ideal. Above 25 °C fermentation accelerates, and so does the chance of spoilage.
Don't rush it. Olives not ready at three months are not spoiled — the variety is simply slower. Decide by tasting.
Storage. A year in brine under a layer of oil, somewhere cool and dark. Two months in the fridge once opened.
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