Actually very easy

Cured green olives

The beliefPeople assume an olive can be eaten off the tree, and that its bitterness is a matter of variety.

The truthNo olive is edible raw. Its bitterness is one molecule, and water or salt draws it out over months.

Half an hour of work, three months of waiting

How to make it

What you need

3 kg green olives
For the brine: 100 g rock salt per litre of water
Lemon, bay leaves and garlic
Glass jars and a weight

How the engine read this list (6 lines)

3000 g	Green olives	green-olive
100 g	Rock salt	salt
1000 g	Water for the brine	water
—	Lemon	lemon
—	Bay leaves	bay-leaf
—	Garlic	garlic

An empty weight means that line could not be turned into grams — either the amount is open ("to taste") or the ingredient has no record here. Neither enters the sum as zero; they do not enter it at all.

Sort the olives, discarding bruised ones. Crack each lightly with a wooden mallet or score it two or three times: without an opened surface the bitterness will not leave for months.
Put them in a wide container, cover with fresh water and change it daily for ten days. The water yellows less each day, and that is how you watch the bitterness leave.
Make the brine at 100 g of salt per litre. To check the strength, float a raw egg in it: a coin-sized patch showing above the surface means the ratio is right.
Pack the olives into jars with slices of lemon, bay and garlic between them, pour the brine over and weigh everything down beneath it.
Keep them somewhere cool and dark for three months, tasting weekly through the first month. When the bitterness has gone, top each jar with a finger of olive oil and close it.

Why it works

An olive’s bitterness comes from a phenolic compound called oleuropein, and it is so dominant that a raw olive is effectively inedible. There are three ways to remove it and all do the same thing: move the oleuropein out. Water curing is the slowest and most natural — daily changes of water carry the compound out by diffusion over 20 to 40 days. Brine curing draws the bitterness out and starts a lactic fermentation at the same time: in 8–10% salt water the bacteria turn sugars into acid, the pH falls below 4, and the olive both sweetens and keeps. The third route, lye, is industrial: sodium hydroxide breaks the oleuropein down chemically and delivers in a day — taking the texture and much of the aroma with it. At home the right method is brine: it asks for patience, but it leaves the olive an olive.

The rough sum

4100 grams going in

4350 kcal in total

100% of the mass has figures behind it. This is the sum of what GOES IN rather than of what comes out. Wherever something evaporates, drains or ferments the two differ: a kilo of milk is 150 g of cheese.

Diets it qualifies for

Gluten-free Vegan Vegetarian Lactose-free

Storage & shelf life

How long it keeps

In brine, cool and dark: 1 year
In brine, in the fridge: 2 years
Out of the brine, under oil: 1 month
Out of the brine, exposed: 3 days

Olives are preserved by salt and acidity working together, and both weaken with time. Since the brine is diluted by the olives’ own water, refreshing it every six months helps. The film of olive oil on top shuts out oxygen and markedly delays surface yeast — it is a technical layer rather than a flourish. Olives going soft say the salt has fallen; shrivelled olives say it is too high. Both are corrected by adjusting the brine.

When to bin it Slimy or stringy brine, or a sharp rotten smell, means the whole jar goes. So does fuzzy or coloured mould — do not skim it and eat the rest.

History

Where it comes from

The olive is the Mediterranean’s founding plant and has been processed in Anatolia for eight thousand years; olive stones found in the Aegean prove it. Working out how to remove its bitterness was a chemical discovery rather than an agricultural one: nobody guesses that a fruit becomes edible after three months in water, and that knowledge accumulates only by trial and transmission. The difference between cracked, scored and whole brined olives is technical rather than a matter of taste: the more the surface is opened, the faster the oleuropein leaves — cracked olives sweeten in three weeks, whole ones in three months.

The knack

Avoid metal lids: brine is both salty and acidic, it eats the metal and the olives take on the taste.
Skim any white film and push the olives back under. It is kahm yeast: harmless, but it flattens the flavour.
Black olives do not take the same treatment: a ripe olive has less oleuropein and more oil, and is cured in dry salt instead.

Fermentation