Olives: How They Became Edible

Every other food in this section was already food before anybody pickled it. A cucumber is a cucumber. A herring is dinner. The olive is the one thing here that is inedible on the branch, which means somebody, at some point, worked out how to fix that — and the obvious question is how, and which way was first.

I had a picture in my head of how it might have gone. An olive falls into the ashes of a fire. Rain comes. The rain turns the ash into lye. Days later somebody picks the olive up and it is not bitter any more.

I want to say straight away that the chemistry in that picture is sound. Wood ash and water do make an alkaline solution, and alkali is exactly what breaks oleuropein. But the archaeology says the sequence is inverted — and the way it is inverted is more interesting than the story I was telling myself.

The short answer

Water and salt were first, by roughly four thousand years. Ash and lime came far later, and when they arrived they were not the discovery that made olives edible — people had been eating cured olives for millennia by then. Alkali is a speed upgrade. It took a month down to a day.

So the ash did not solve the problem. The ash solved the waiting.

What was actually found, and where

The best evidence comes from two submerged Chalcolithic villages off the Carmel coast of Israel, drowned by rising sea level and excavated underwater.

Kfar Samir, at around 7,000 years before present, is the earliest known olive oil production anywhere — crushed pits, pulp, and a heavy olive pollen signal. Which is worth pausing on by itself: the first thing anybody did with an olive was crush it, not cure it. Oil is the older technology. The table olive is the later invention.

Hishuley Carmel, a few hundred years younger at 6,656–6,450 BP, is the other one, and it is the one that answers the question. Published in Scientific Reports in 2021, it is described by its authors as the earliest evidence for large-scale table olive production, and they note it predates the historical evidence for consumption of table olives by almost four millennia.

How they can tell a table olive from an oil olive

This is the part I like, because it is a genuinely clever piece of reasoning from almost nothing.

They counted broken pits. Oil production crushes the fruit, so an oil site leaves you smashed stones. Curing does not crush anything, so a curing site leaves you whole ones.

Site	Pits sampled	Intact
Hishuley Carmel (table olives)	3,113	48%
Kfar Samir (oil)	5,106	15.6%

Some of the Hishuley Carmel pits still had fruit pulp attached — which is not what waste from an oil press looks like. It is what a fruit that was soaked and rinsed looks like.

And the method they infer is the boring one

The authors’ conclusion, verbatim: the structures “were used to prepare table olives for consumption, probably by curing them in sea water or in salt.” They point at the obvious reason — the site sits on the Mediterranean, which is “a source of both sea water and salt required for debittering/pickling/salting the fruit.”

They then went and tested it. 600 Suri olives, three treatments — seawater at about 3% salt, seawater brought up with 8% sea salt, and tap water at 11% NaCl — tracked for 112 days. A separate dry-salting pilot using wild olives and coastal sea salt produced edible olives in 20 days.

⚠ What this does and does not establish. It establishes that people were curing table olives at scale seven thousand years ago and that seawater and salt do the job. It does not establish that this was the first time anyone ever did it — the same literature says plainly that the origin of debittering “is as yet undated.” What survives underwater is what was thrown away in quantity at a village that happened to drown. Absence everywhere else is not evidence.

Then the record goes quiet for four thousand years

And when it starts up again it is Roman farm manuals, and there is still no lye in them.

Columella, De Re Rustica XII.49, first century AD, is the fullest account. Bitter olives harvested in autumn, crushed and soaked in warm water, drained, then packed with fennel and mastic seed and toasted salt, covered with must — grape juice — and sealed. Edible in three days. He gives a brine version too, and for black olives a dry salt cure: about thirty days draining under salt, then rinsed and jarred.

Read that list again. Water. Salt. Brine. Time. Every one of the methods on the olive page except the lye.

Cato, two centuries earlier, gives epityrum — a chopped olive relish with oil, vinegar, coriander, cumin, fennel, rue and mint. That is a dressing, not a cure; the olives were already edible before they got there.

So when does the ash show up?

Later, and I cannot tell you exactly when — which I would rather say than invent.

The International Olive Council, which is the trade’s own body, puts it in one sentence: “In the past, olive or oak ash — and sometimes lime — was used to remove bitterness.” So the practice is real and the IOC treats it as historical. What the IOC does not do is date it.

🔴 And here is the one specific date I found, and why it is not on this page as a fact. Several food-history pages attribute an ash-and-lye olive cure to Palladius, the fourth-century Roman agricultural writer, complete with a quoted recipe involving sifted cinders, old wine and cypress leaves. I went looking for the passage. The chain runs blog → blog; I could not get it back to Rodgers’ Latin text or to Fitch’s 2013 translation, and I do not have a copy to check. It may well be perfectly true. But this section has already caught itself once believing a confident, much-repeated date that turned out to be a trade body citing a magazine, so I am recording it as unverified rather than printing it and moving on. If somebody has Palladius on the shelf, I would genuinely like to know.

⭐ Why ash is not quite lye, and why lime keeps turning up beside it

This matters for the story, because it is the reason the ash step was a partial answer rather than the finished one.

Leach water through wood ash and what dissolves is mostly potassium carbonate — potash. In water that gives you a properly alkaline solution, because carbonate pulls protons off water, and alkaline is all you need to start hydrolysing oleuropein. That is why the picture I had in my head works at all.

But potash is not a hydroxide, and it is a good deal gentler than one. To get an actual strong alkali out of ash you have to causticise it: add slaked lime, and the calcium takes the carbonate, leaving potassium hydroxide behind. Which is exactly why the IOC sentence says “and sometimes lime.” The lime is not an alternative to the ash. The lime is what makes the ash serious.

And sodium hydroxide — the stuff in the bottle, the thing every modern recipe means by “lye” — is an industrial product. Cheap soda ash only arrives with the Leblanc process at the end of the eighteenth century and the Solvay process in the nineteenth; electrolytic caustic soda is later still. The lye cure as we now practise it is younger than the steam engine. The olive is not.

The California ripe olive, and a credit that gets handed to the wrong achievement

Freda Ehmann is regularly described as having invented the lye cure. She did not, and it is not a close call — alkali curing predates her by centuries and the IOC’s ash sentence predates it by longer.

What she did do, from an olive grove outside Oroville, California, starting in 1898, was build the first serious American business out of a canned, oxidised, shelf-stable “ripe” olive, working with researchers at the University of California. ⚠ Even that is muddled in the sources I read: some name Eugene Hilgard, others credit George Colby and Frederic Bioletti with the canning method specifically. I have not resolved which, so I am naming all three and the institution.

🔴 And the olive she made is a green olive

This is the fact that reframes an entire supermarket aisle.

A California “black ripe” olive in a can was not black when it was picked, and it was not ripe. It is picked green. Then:

1. Lye, at around 1% sodium hydroxide, in repeated soaks.
2. Air blown through the water between soaks — this is the actual step. Oxygen polymerises the olive’s own phenolic compounds and they go dark.
3. Ferrous gluconate (or ferrous lactate or sulphate) to fix the colour, because the pigment that oxidation produces is not stable on its own.
4. Canned and heat-sterilised.

The blackness is manufactured. The iron salt on the ingredients panel is not a dye in the cheating sense — it is a mordant holding a colour the process created — but the olive did not arrive at that colour by ripening, and “black ripe” is a trade term, not a description.

Which explains the taste. A canned black olive is mild and uniform and slightly hollow because nothing lived in it and nothing was allowed to. Compare the brine-cured Kalamata, which spent eight months being fermented by bacteria. Same fruit. Different amount of biography.

The order it actually happened in

Roughly when	What	What it is doing
~7,000 BP	Crushing for oil	Not a cure at all — the oldest use of the fruit
~6,600–6,450 BP	Seawater, brine, dry salt	Leaching and osmosis. Slow, safe, no chemistry required
Classical era	The same, written down (Columella, Cato)	Refinement, not innovation
Undated, pre-modern	Wood ash, sometimes with lime	The first alkali. Faster. Weaker than what came next
19th–20th c.	Sodium hydroxide	Industrial alkali. Hours instead of weeks
1898 onward	Lye + forced air + iron salt	The canned “ripe” olive. A new product, not a new cure

⭐ So: was I right about the fire?

Half. And the half I was wrong about is the half I would not have guessed.

The mechanism holds. Ash and rainwater really would debitter an olive, slowly and unevenly, and ash really is the first alkali anybody used on this fruit.

The chronology does not. By the time anyone was leaching ash, olives had been a preserved food for thousands of years. Nobody was standing over a fire pit solving “how do we eat these?” — that was solved. They were solving “how do we stop waiting a month?”

And the honest ending is that there is no record of the discovery at all, by fire or otherwise. My ash story is a just-so story. So is every other origin tale for this — including the tidy ones told with more confidence than mine. What we have is a heap of unbroken olive pits on a drowned Chalcolithic beach, and the fact that whoever left them there had already worked it out.

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Next: Which Olive, and What For — one species, hundreds of cultivars, and the reason you cannot make a Castelvetrano out of a Kalamata. Or back to Olives for the methods themselves.