The short answer to "Are olives a fruit?" is yes. But don't stop there! Learning more helps explain about the flavor and health benefits of extra virgin olive oil and table olives.
Let's start with the botany: olives are the fruit of Olea europaea—the olive tree. They are a drupe, or stone fruit, botanically similar to the cherry, plum, almond and peach. The part of the olive fruit that we eat is the fleshy mesocarp. That takes care of the trivia quiz question!
An interesting fact about olive oil is that it is a rarity because the oil comes from the flesh of the fruit. Every major edible oil—except avocado—is extracted from the seed. This is why extracting virgin olive oil is a more gentle process than extracting seed oils and does not require solvents. The olive pit contains little, if any, oil; the lower oil yield when pits are removed is more likely due to the lack of the mechanical action of the pit fragments helping break up the olive flesh.
Why are some olives green and some black?
Green olive or black olive, it's the same fruit. All olives start out green, and turn black as they ripen. Most olives go through a purple phase on the way to being completely dark. As with grapes, the time of turning color is called "veraison." Olives to make table olives can be picked at any ripeness: completely green, completely black, or anywhere in between. Black olives of the sort popular in the US are actually picked when green and turn black in the curing process. But a Kalamata olive, for example, is picked after it has turned color. Oh, and those little red pimentos in your martini olive? Always added afterwards—they never grow like that!
There is great variability among different olive cultivars (also called olive varieties). The fruit ranges in size from the size of a Spanish peanut to the size of a small plum. The shape can go from almost round and symmetrical, to curved and pointy. And the levels of "minor components"—polyphenols, squalene, vitamin E, etc.—vary a lot by olive variety as well. This is part of what influences the flavor of the olives or olive oil.
What's different about green olives?
In addition to differences due to olive variety, unripe green olives are generally higher in the minor components, including polyphenols, that are showing multiple health benefits in research. These components show antioxidant and anti-inflammatory benefits, and contribute to lower blood pressure, improved cholesterol profiles by lowering LDL and raising HDL, and help prevent diabetes, some cancers and cognitive decline.
The compounds that makes olives taste bitter, primarily oleuropein, are higher in unripe olives. This means you can expect a more bitter flavor from a earlier harvest oil. The same is true for the peppery (aka pungent) character: this is likely to be more prominent in early harvest extra virgin olive oil.
Does this mean you must always use intense green extra virgin olive oil? Definitely not! As olive fruit ripens there is a decline in some of the minor components, but there are still many healthy benefits so use an olive oil that you enjoy. Experience indicates that people tend to start with milder olive oils and gravitate to more intense ones over time—the same as with wines.
Is olive oil fruit juice?
Does that mean that extra virgin olive oil is a fruit juice? If you look at the FDA definition, it says, "Juice means the aqueous liquid expressed or extracted from one or more fruits or vegetables, purees of the edible portions of one or more fruits or vegetables, or any concentrates of such liquid or puree."
By that definition it is a stretch to call extra virgin olive oil a fruit juice. One of the steps in making olive oil is the removal of all the "aqueous liquid"—in fact in the olive mill it's often referred to as "wastewater." Referring to extra virgin olive oil as "fruit juice" is a marketing thing: producers do it to emphasize that extra virgin olive oil is a fresh natural product. But unlike fresh orange juice, it is shelf stable, maintaining its quality for two years under proper conditions. And of course, most people think of juice as a beverage—olive oil not so much!
Whatever you want to call it, eat it up!
So it's really up to you. If the idea of extra virgin olive oil being a fruit juice resonates with you, great. But if it doesn't, don't let it put you off. The health benefits of the Mediterranean diet are due both directly to the consumption of olive oil, and indirectly due to the way good olive oil makes healthy foods like veggies and legumes taste fantastic and easy to enjoy. Think of extra virgin olive oil as your secret ingredient in the kitchen and at the table, adding deliciousness to your every meal!