Illustration by H.M. Herget, Nat Geo Image Collection
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A 1944 artist's rendering suggests how ancient Greeks may have harvested olives for oil.
Illustration by H.M. Herget, Nat Geo Image Collection
The Plate

The Bitter Truth About Olives

Thank goodness we figured out how to press olives into oil, because eating them raw is not a pleasant option.

A luscious-looking olive, ripe off the sun-warmed tree, is horrible.

The substance that renders it essentially inedible is oleuropein, a phenolic compound bitter enough to shrivel your teeth. The bitterness is a protective mechanism for olives, useful for fending off invasive microorganisms and seed-crunching mammals. In the wild, olives are dispersed by birds, who avoid the bitterness issue by swallowing them whole.

Given the awfulness of the au naturel olive, you can’t help but wonder why early humans, after the first appalling bite, didn’t shun the olive tree forever.

The answer, of course, is olive oil. The olive is a drupe or stone fruit, like cherries, peaches, and plums, in which a fleshy outer covering surrounds a pit or stone, which in turn encases a seed. In the case of the olive, the outer flesh contains up to 30 percent oil—a concentration so impressive that the English word oil comes from the ancient Greek elaia, which means olive.

Archaeological and scientific evidence indicates that the olive tree (Olea europaea) was most likely first cultivated on the border between Turkey and Syria, spreading from there throughout the Mediterranean, to Israel, Palestine, Jordan, Lebanon, Greece, Italy, France, and Spain. People in the eastern Mediterranean have been grinding olives for oil the last 6,000-8,000 years. Olive oil was used for cooking, cosmetics, medicine, and in lamps. The original Olympic torch burned olive oil. The ancient city-state of Athens was said to have been named for the deity who gave Greek culture its greatest gift: Poseidon made a bid for the prize by producing the horse, but Athena won hands down by creating the olive tree.

The Old Testament is awash in references to olives, listed along with such desirables as honey, figs, grapes, and pomegranates. To destroy an enemy’s olive trees, in Old Testament days, was the ultimate act of war. “Except the vine,” wrote Pliny the Elder in the first century CE, “there is no plant which bears a fruit of as great importance as the olive.”

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Olives ripen on a tree in Duoro Valley, Portugal.

According to food writer Harold McGee, it was the Romans who most likely came up with the technique that put the olive fruit itself on the dinner table. Earlier people had discovered that olives could be debittered by soaking them in repeated changes of water, a painstaking process that took many months. This was somewhat improved by fermenting the olives in brine, which was marginally quicker, but the Romans found that supplementing the brine with lye from wood ashes (sodium hydroxide) cut the time required for producing an edible olive from months to hours. (See this Roman recipe for spiced olives.)

Olives came to the Americas with the Spaniards: an olive grove was planted in Lima, Peru, in the mid-16th century; and Spanish Franciscans planted olives in mission gardens in California in the 1700s. While these west coast olives thrived, however, attempts to establish olives on the east coast fizzled.

Jefferson was an early olive fan: after an olive-observing Mediterranean vacation taken in 1787 while serving as America’s ambassador to France, he pronounced the olive “the worthiest plant to be introduced in America” and “the richest gift of heaven.” After frost thwarted his efforts at Monticello, he petitioned the South Carolina Society for Promoting Agriculture to plant olive trees. Encouraged, he had 500 olive cuttings shipped home from Aix-en-Provence. Like the Monticello plantings, however, these failed to survive. Jefferson blamed the South Carolinians for neglect and lack of enthusiasm, but chances are the faulty party was the climate: the southeastern United States was too humid to support olive trees.

Over 95 percent of American olives come from climate-friendly California, though this still constitutes less than one percent of the world olive market. Today the lion’s share of global olives comes from Spain. In many places in Europe, olive trees are suffering from disease (See Europe's Olive Trees a Are Dying.)

About 90 percent of the world’s olive crop goes to make olive oil. The remainder is harvested for table olives which, though there are over 2,000 known olive cultivars, are known to most of us in two colors: green and black.

Green olives, the kind found in martinis, are picked green and unripe and then cured. These are often called Spanish olives. Tree-ripened olives, left to themselves, turn purple, due to an accumulation of anthocyanin—the same pigment that puts the purple in Concord grapes.

Black olives, though labeled as “ripe” on supermarket cans, actually aren’t: these, a California invention, are green olives that have been cured in an alkaline solution, and then treated with oxygen and an iron compound (ferrous gluconate) that turns their skins a shiny patent-leather black. Olive aficionados don’t think much of these, though in my experience, kids love the pitted versions, which are tailor-made for sticking on the ends of fingers.

There’s no need to stop here, however: there’s a wide range of scrumptious olives that many of us never see. For adventurous olive-eaters, check out A Beginner’s Guide to Olives: 14 Varieties Worth Seeking Out.

One last fact: Vincent van Gogh, who appreciated olives, painted 19 pictures of olive trees.