Curing green olives from an October crate, one water change at a time

i. Buying and cracking

The olives I buy are usually a firm, medium-sized green variety that the stallholder calls by the name of a town an hour inland. They need to be firm, unbruised and still green, not yet turning purple, and I pick through the crate by hand, which the woman who sells them tolerates with good humour. Four kilos is my limit, because every one of them has to be cracked, and every one of them will need a place to sit in water for a fortnight in a kitchen with very little floor.

Cracking means giving each olive one sharp tap with a flat stone or the base of a heavy glass, enough to split the flesh on one side without breaking the stone. It lets water reach the bitter compounds inside and roughly halves the time needed to remove them. I do it on a chopping board on the balcony table with the radio on, and four kilos takes about an hour and a half. Slitting each olive with a knife works too and gives a neater finish, but it is slower and my hands prefer the stone.

ii. Two weeks of water

The cracked olives go into the largest jars and a food-grade bucket, covered completely with cold water and held under with a plate. Every morning I pour the water off, which comes out brown and bitter and faintly stains the sink, and refill with fresh. The kitchen fills with a smell somewhere between cut grass and wet wood, which my neighbours on the landing have learnt to ask about.

I taste one olive every few days from the third day onward, bitten and spat out. The first season I stopped at ten days, which was too early, and the finished olives had a harshness at the back of the throat that never left. The second season I went to fifteen days and the olives were still pleasantly bitter but no longer unpleasant, which is where I want them. The right point is when the bitterness is a flavour rather than a warning, and only tasting finds it.

Space is the real difficulty in a small flat. Four kilos of olives in water fill two large jars and a bucket, and for a fortnight they occupy the floor beside the fridge where the recycling normally lives. A woman two floors down who has done this every autumn of her life told me her mother simply kept the olives in a bucket on the roof terrace and changed the water when she remembered. I have not been brave enough to leave them on the roof, but I have stopped apologising to visitors about the bucket.

• Days 1 to 4: water very dark, olive tastes of nothing but bitterness
• Days 5 to 9: water lighter each morning, flesh starts to taste of olive
• Days 10 to 13: bitter at the finish, the flesh softening slightly at the crack
• Days 14 to 16: the point I stop, still firm, bitter only as a flavour

iii. Into the brine

Once the water cure is finished, the olives go into a strong brine, which is a different thing from the vegetable brines in the rest of this notebook. I use ninety grams of coarse sea salt to the litre of water, dissolved warm and cooled completely, and pour it over the olives packed with wild fennel stalks, strips of orange peel, crushed garlic, a few bay leaves and some thyme from the pot on the balcony. The flavourings are the local way of doing it as far as I can tell from the stallholders, and I have not found a reason to change them.

The olives are edible after about a week in brine but get far better after a month, when the fennel and orange have gone all the way through. They keep in the brine in a cool cupboard until spring, and I take out a small jar at a time and rinse them briefly before serving. A thin film sometimes forms on the surface of the big jar over the winter, which I lift off and top up with fresh brine at the same strength.

iv. What I would do differently next October

The main lesson from two seasons is that the water cure cannot be rushed and the brine can hardly be overdone. The first year's olives were too bitter and slightly too soft, because I changed the water in a warm kitchen at irregular times and skipped two mornings on a work trip. The second year I set an alarm, kept the bucket in the coolest corner, and asked the neighbour opposite to change the water on the one weekend I was away. The difference in the finished olives was obvious to everyone who tasted both.

Next October I want to try a second variety alongside the usual one, a smaller olive I have seen on one stall near the end of the season, and to keep a proper day-by-day tasting log instead of the loose notes on tape I have now. The notebook has room for it. The olive jars are the ones people ask me about more than anything else I make, and they are the ones that taught me the most patience.