Olive oil is a monounsaturated oil that resists oxidation and hydrogenation. Monounsaturated oils contribute to good health and do not increase cholesterol or cause hardening or clogging of the arteries like some saturated fats.
When looking for a good olive oil, do try to find one that is organically grown to minimize your exposure to pesticides, if possible. Purchase in containers of a quantity that you can easily use within 6 months, and preferably those bottled in dark glass, and then store the tightly sealed bottle in a cool, dark space.
Taste is definitely a personal preference, but not necessarily an indicator of quality. A broad range of flavors exist among oils, due to the time of year the olives were harvested, the location in which they were grown, and the variety of the olive trees that produced them. If possible, purchase from a source that allows you to taste beforehand, or buy a very small quantity to be sure it is to your liking. Italy, Spain and Greece are known for their excellent olive oils, but California has also begun producing some really great oils, as well. (Some sources claim that California olive oil is preferable because our domestic standards for determining quality are considered more strict than foreign standards.)
Virgin olive oil has been obtained from the olives by only mechanical means, meaning no heat, chemicals, radiation or microwaves have been used in the extraction process. Extra-virgin oils are cold-pressed, which minimizes any change at all to the oil and produces an oil with an acidity lower than 1%. It is considered of the highest quality and is delicious on salads or as a finishing oil where a perfect, fruity taste can most be appreciated. Ordinary virgin olive oil has a higher acidity, and the flavor does not break down during cooking like extra virgin olive oil. It can also be used for baking. For this reason, it is probably one of the most versatile oils to have in the kitchen.
Regular olive oil has a higher smoke point – the point at which the oil begins to smoke, or burn – which means that you can cook with it over higher heat than with virgin olive oil. Still, 250°–325° is about as high a heat as you would want to use when cooking with olive oil. Anything over that results in the destruction of natural antioxidants and the creation of free radicals.