Olive oil is made by gently crushing and pressing olives until the oil is separated from the fruit pulp. The flesh of a ripe olive is about half oil. When the skin of a just ripe olive is broken, the first oil to flow from the flesh is called “virgin” or “sublime” or “first expressed” oil.
The best oil comes from olives picked just after ripening, before the olive turns black. Oil from olives not ripe or too green will be bitter. Oil from olives too ripe will be rancid.
When olives are crushed and pressed, the pit at the center of the fruit is not broken. At the crush, the flesh of the olive fruit is turned into a paste. From the paste, the oil is extracted in droplets by the pressure of a press (traditionally a stone press, more recently metal rollers) and sometimes by the use of a centrifuge. After the first or “virgin” crush a solid pomace remains from that additional oil can be processed which is less pure or natural. The time to extract the oil from olives–from crush to bottling–can be a few weeks to a few months.
The most flavorful and sought after olive oil is the purest and most natural–the oil from the initial crush or pressing is called “extra virgin.” Like wine and cheese, olive oil can reflect terroir (a French term)–that is the flavor of the environment where the olive was grown including the degree and fluctuation of temperature and humidity during the growing season, minerals in the soil, air and water purity, and even the plants and animals growing close by. Thus just pressed olives oils may be described as light and fruity, strong and forceful, and with differing degrees and flavor or spiciness.
Olive oil is one of the most digestible of the edible fats. It is the only vegetable oil that can be consumed freshly pressed from the fruit. Extra virgin olive oil is best for dipping, drizzling, brushing on vegetables and meats before grilling and for mixing in dressings, marinades, and sauces. Extra virgin olive oil has a low smoke point so it is best not used for cooking.
Keep reading for how olive oil is classed, stored, and cooked.
Olive oil is described by how the oil is extracted from the fruit as well as additional, if any, processing. “From hand-picked olives” is sometimes the initial description of an olive oil, it implies that the olives were hand selected at the exact ripeness desired and not mechanical harvested–which could allow for the inclusion of over or under ripe fruit.
First cold press. First cold press olive oil is oil from the first “pressing” of whole unblemished olives. First cold press oil is the least processed olive oil. It is the first oil to come from the press of the olives. No heat which can change the oil’s chemistry is used. The term “cold pressed” is applied because the oil is extracted by only mechanical pressing. Cold pressed and extra-virgin oil will contain no more than 1 percent oleic acid, the acid which gives olives their bitter taste. Cold pressed olive oil is usually pressed within a day of harvest and is the most pure and natural olive oil.
Extra virgin. Extra-virgin olive oil is another way to describe oil from the first “cold pressing” of whole unblemished olives. Extra-virgin oil is the least processed olive oil, no heat or chemicals are used to extract the oil, only mechanical pressing. Extra-virgin oil will contain no more than 1 percent oleic acid, the acid which gives olives their bitter taste.
Virgin. Virgin olive oil comes from the second pressing of the olives. Virgin olive oil comes only from mechanical or “cold pressing” just as extra-virgin oil, but virgin olive is not the first oil extracted. Virgin olive oil can contain up to 2 percent oleic acid. The flavor of virgin olive oil will not be as pure as extra virgin olive oil.
Ordinary virgin. Ordinary virgin oil is the least flavorful of cold pressed olive oil and can contain up to 3.3 percent oleic acid. This oil can be used for frying where flavor is not essential.
Pure. Pure olive oil or “100% pure olive oil” is actually a combination of refined olive oil and virgin olive oil. Pure olive oil is processed; it has been filtered and refined often using heat or chemicals and is not “virgin.” Pure olive oil is sometimes labeled “olive oil.”
Light or extra light. Light or extra light olive oil is a combination of processed olive oil and other processed vegetable oils. Light olive oil is not pure olive oil.
Storing olive oil. Keep olive oil in a cool dark place tightly sealed. Light, air, and high temperatures will cause olive oil to spoil and turn rancid. Store oil in dark colored glass bottles so that light does not affect the oil. Fresh olive oil should always be favored. Olive oil deteriorates with time and becomes stale. Use olive oil within a year for the best flavor and fragrance. Use oil more than a year old for cooking, not for dipping or drizzling or use on salads and in dressings.
Cooking. Use refined olive oils for cooking. Extra-virgin olive oil will burn at temperatures near 350°F (180°C); the taste will be unpleasant.
How olive oil is pressed. Need more detail? Here is how olives are crushed and pressed to extract olive oil. First the olives are crushed or ground into paste using large millstones or metal rollers. The olive paste usually stays under the stones for 30 to 40 minutes. The oil collected during this initial pressing is called first pressed or extra virgin oil. After the initial grinding, the olive pulp or paste is spread on fiber disks or a coarsely woven fabric which is folded to make pulpy blocks or “cheese,” about a yard square and 3 inches thick. These blocks are stacked on top of each other, often with slats between them. The blocks are placed into the press and pressure is applied. From this second pressing a lower grade of oil is extracted. Oil from each pressing is filtered through a woolen cloth or fiber and allowed to settle at the bottom of tin or glass lined settling tank. The oil stands for several weeks and sometimes up to five months. During this time, sediment is drawn from the tanks several times before the oil is finally bottled.
Pictured above: Just harvested olives on the way to the crush.