It can be hard to reconcile the hard green and purple fruit growing on silvery leafed, gnarled trees with the olives we eat. An olive straight from the tree doesn't seem edible: it's mouth-puckeringly bitter - the fruit needs to be cured, pickled or otherwise processed for it to be palatable. Whether an olive is green or purple (these turn black when processed) depends on their ripeness. The species is famous for its longevity as well as its ability to withstand extreme growing conditions, and the tree and its products are revered in some cultures and religions. In modern times, olive oil has become known as a healthy fat - it is monounsaturated and said to be good for the heart. Whole cured olives can be easily pitted by lining them up a few at a time on a chopping board. Use the flat blade of a chef's knife to press on the olives firmly and roll them slightly under the knife. This loosens the pit, which can be pulled out by hand. If you have an abundance of olives, make them into the delicious, pungent dip called tapenade. Pit the olives then roughly chop them with capers, garlic, olive oil, mashed anchovy, fresh lemon juice and black pepper. You can use a food processor to chop the ingredients, but don't purée them too finely; the mixture should have a coarse texture. Serve the tapenade with crudités or spread it on thin pieces of toast.