Curing olives at home

A raw olive is genuinely inedible. Not unpleasant, inedible: there is a compound in it called oleuropein that is so bitter it makes your whole mouth contract. Everything in curing is about getting that out, and there are only two ways to do it. One is a lye bath, which takes about two days. The other is water and time, which takes months. This is the second one.

Picking

We pick Maçanilha Algarvia in the second half of October, hard and green, before there is any colour on them at all. Green olives cure firmer and take longer. If you pick them turning purple they will cure faster and end up softer, which some people prefer.

Sort as you go. Anything bruised, split, or with a hole in it goes out. A damaged olive will go soft in the brine and it will take its neighbours with it.

Cracking

Each olive gets cracked, which means hitting it once with a flat stone or the flat of a wide knife hard enough to split the flesh open without shattering the stone. A shattered stone puts fragments through the whole batch. This is the traditional treatment for the green Maçanilha here, and the point is to open a channel so the water can reach the flesh.

The alternative is slitting each olive twice lengthways with a knife, which is slower, or leaving them whole, which works for black olives and takes considerably longer. Cracking a bucket of olives takes two people an evening and is the only real work in the whole process.

The water stage

Cracked olives go into a bucket of plain cold water, weighted down with a plate so they stay under, and the water is changed every single day. Not every other day. Every day, for about ten days.

Around day eight, start tasting one. It should still be bitter but it should be a bitterness you can hold in your mouth rather than one that makes you spit. When you get to that point, stop. Going further makes them bland and it is the most common mistake, because after eight days of changing water there is a strong urge to keep going and get it perfect.

The water will come off brown and cloudy for the first few days. That is what you want to see.

Getting the brine right

Ten per cent brine, which is 100 grams of salt to a litre of water. Weigh it. The traditional test is to float a raw egg in the brine and adjust until a coin sized circle of shell shows above the surface, which is a reasonable check if you have no scales and a nonsense if you do.

Use non iodised salt. Iodised salt can put an off flavour into a long cure. Boil the water, dissolve the salt, and let it cool completely before it goes anywhere near the olives.

Into brine, and then waiting

Olives into clean jars, brine over them, and aromatics if you want them. We use a bay leaf, a strip of lemon peel, a piece of garlic and a little oregano off the bank. Nothing more complicated than that and it is a matter of taste rather than technique.

Everything must stay under the brine. Anything sitting proud of the surface will go mouldy and it will be the thing that ruins the jar. A small clean weight, or a folded vine leaf, or in our case a piece of the olive branch wedged across the neck.

Then wait. They are edible after about six weeks. They are properly good after four months. The October pick goes into jars in November and we do not open them until February, and every year the batch we opened early was noticeably worse than the one we left.

What goes wrong

A white film on the surface. This is almost always a harmless yeast. Lift it off, check the olives underneath are still firm and smell clean, and top up the brine. If it is fuzzy, coloured, or smells sour rather than briny, throw the jar out.
Soft olives. Usually a brine that was too weak, or fruit that was already bruised when it went in. There is no fixing it.
Olives that are still savagely bitter after four months. The water stage was too short. You can go back: take them out, another five days of daily water changes, fresh brine, another six weeks.
Salt that is too strong, which is fixable. Soak them in fresh water for a few hours before eating.

Two things not to do

Do not seal olives under oil for storage unless you know exactly what you are doing. Plant material under oil at room temperature is the textbook setup for botulism, and there is no reason to take the risk when brine works perfectly. It is the same reason we strain the chillies out of our chilli oil.

Do not use a lye cure at home unless you have read properly about it first. Food grade sodium hydroxide is genuinely caustic, it burns skin and eyes, and while it is a completely legitimate commercial method, it is not something to try casually because a video made it look quick.

How long they keep

A year in the brine, sealed, somewhere cool and dark. Once open, in the fridge, olives under the brine, three weeks. Ours go into jars as table olives in February and last until the following autumn.