Olives are fruits that grow on trees in climates similar to the Mediterranean Basin. Olive trees are some of the oldest fruit trees domesticated by humans, potentially being grown for purposes of harvesting as far back in time as 5000 BC.

Olive trees can live for a very long time. Some of the oldest still-living olive trees like the Olive Tree of Mouchão are ~3350 years old. You don't even know anyone that old!

For about as long as we've grown them, people have pressed olives into Olive Oil using a device similar to mills that grind grain into flour. In ancient Greece, olive oil was highly prized and often exported. The demand for oil cemented the olive as a staple crop in Greece and later the rest of the Mediterranean. It was used as fuel, food, and valued for its use as a beauty cosmetic.

As a fruit, olives are green until they ripen on the tree, at which point they become purple-black. Riper olives produce more oil, but some say younger olives make richer oil. The olive fruit has a pit, sometimes called a stone, that is the seed of the tree. This is removed before further processing, and in the case of table olives is sometimes replaced by slices of pimento chilis. Previously this slicing and inserting was done by hand. Modern developments in manufacturing technology have allowed producers to purée pimento peppers and reconstitute them into standard-size little strips using a gum. The standardization allows the stuffing of olives to be mechanized.

Fresh from the tree, olive fruit is bitter, and must be cured to be enjoyable. Curing is normally done by one of these methods:

• Salt packing
• Lye bath
• Soaking in brine
• Soaking in water or weak brine

At the grocery store they sell table olives in cans or jars. Black olives come in cans and green ones come in jars. That's because black olives in cans caused cases of botulism in the early 20th century in California. Cans can be heated to temperatures high enough to kill bacteria whereas glass cannot stand these temps.

Any cultivar of olive tree can produce these green or black table olives because the color is just a function of ripeness and method of fermentation; green olives are picked younger than black olives.

However California black olives are picked green, soaked in lye and injected with air repeatedly to push the lye further into the flesh, a process that causes the flesh to oxidize. This gives them their unique black color, especially compared to purple olives which are not cured in a way that oxidizes the flesh.