No one from a Mediterranean culture, where olives have been gathered since about 8000 BC and certainly cultivated since about 3000 BC, would even think of eating them olives raw. Leave it to Americans, though, to invent a “raw food” movement, whose adherents seek out raw olives to eat.
What makes Raw Olives very bitter is a substance in the flesh of the olive classed as a “glucoside.” All glucosides are bitter for the most part, no matter what plant they are in, but the olive’s glucoside, called “oleuropein”, is noteworthy for its bitterness. Oleuropein is also contained in the leaves and the wood of the tree, in case you’re a real raw food fan and are thinking of chomping down on those, too.
You can buy Raw Olives by special order or at some ethnic markets — the main buyers are people from Mediterranean who enjoy processing olives with their own recipes.
To be made edible, Raw Olives are processed by one of several curing methods, which draw out the bitter Oleuropein. Two methods use a liquid of lye or brine; another method cures them dry between layers of salt. Lye treatment tends to draw out far more of the bitterness than the other methods. The catch is, it draws out a lot of the flavour, too. Plain water will also draw out the bitterness, though not as quickly. Merck Index, Eighth Edition, 1968 lists Oleuropein as “moderately soluble in water.”
Very experienced growers will sometimes taste an olive from the tree. These must be old, wizened growers with cast-iron taste-buds, because before the taste of the olive will come through as it is chewed, the taster has to pass first through a fair bit of bitterness that would make anyone else’s face screw up. Even they, though, often test just mature, black olives, which are slightly less bitter than the green.
Literature & Lore
There’s an urban myth that the bitterness is actually a toxin that can harm you, and that curing draws out the toxin, or that lye neutralizes the toxin. In some people’s minds, this is compounded by the book on farming written by Cato (Marcus Porcius Cato 234 BC to 149 BC), in which he notes that the paste left after olives were pressed for oil could be used as an herbicide and pesticide. At least that’s how people paraphrase him. But the truth is — the Romans called this leftover paste “amurca”, and they knew it was bitter. Cato says to get the oil away from it as soon as possible. But what he actually says in “On Farming”, Paras 91 to 101, in which he covers uses for Amurca, is that amurca is useful to keep pests “away”: he talks of sprinkling it on granary floors to deter weevils and mice, coating vines with it so that “no caterpillars will come”, and coating the inside of clothing chests to keep moths away. It’s clear that he thought the smell or taste of it would be a deterrent to pests: he doesn’t give any indication of saying that he thinks it will kill them. As for it being an herbicide, he talks about using amurca as a fertilizer for trees.
Now, you have to wonder why people who believed that Raw Olives were toxic never stopped to asked themselves why olive oil, which is pressed from raw olives, isn’t.
Oleuropein is derived from the scientific name for the olive, “olea europa”.