Extra Virgin Olive Oil is exclusively obtained from olives, through mechanical process (no chemical processes allowed) and in specific thermal conditions, which do not alter the olive oil in any way. It excludes oils obtained by the use chemical processes, and those blended with oils from other sources. It can be qualified as a natural product. Extra Virgin olive oil has a free acidity, expressed as oleic acid, which cannot exceed 0.8 grams per 100 grams (0.8%). The other characteristics (taste, flavour) must correspond to those fixed for this category. Extra Virgin olive oil accounts for less than 10% of oil in many producing countries.
Olives picked earlier in the year may have more polyphenols* and a longer shelf life. The olives reach their full size in the fall but may not fully ripen until late winter. Not completely ripen olives have slightly less oil, more bitterness but are higher in polyphenols. The olive oil made out of not fully ripen olives, tends to be more expensive because there is a lower quantity of olive oil in not fully ripen olives but because of the higher quantity of polyphenols and antioxidants, early harvested olives produce olive oils which have a much longer shelf life. The peppery and bitter quality and flavour notes of grass, green, green leaf, pungent, astringent are used to describe early fall harvested oils.
*Polyphenols reduce the risk of cardiovascular disease and cancer.
The hand picked olives produces a better olive oil than fruit harvested with a shaker, rakes or row type harvester. Mechanical harvesting easily bruise the fruit with a consequent increasing in acidity. Also this method can't also be used in early harvesting since the olives, being not completely ripen, have a strong resistant stem and can only be picked. In most cases nets are placed under the trees and the olives are allowed to drop for weeks as they ripen. Remaining olives are beaten from the tree and the nets gathered. Some olives may have been off the tree for weeks or months, spoiling in the interim. Olives badly bruised during picking will become rancid before being pressed. Polyphenols and other natural antioxidants in the oil will help keep the oil from going rancid. Some varieties have more antioxidants than others. The Tuscan varieties: Frantoio, Moraiolo, Pendolino, and Leccino tend to be high in polyphenols.
Live olives start to die when picked. The longer it takes to get to the mill, the more the final olive oil will be oxidized . To produce a superior extra virgin oil, the olives will need to get to the mill within 48 hours of picking, also making sure they are well ventilated during this period time.
"Cold pressed" is a marketing label description for olive oil not really cold produced by continuous centrifugal presses. Today the paste is almost always warmed during the malaxation** process, before being centrifuged, using horizontal decanters (Olives are harvested in the winter when it is cold). According to IOOC regulations this is still considered "cold pressed". Heating the paste during malaxation will extract more oil but will hasten oxidation, anyway most of the producers are interested in extract more oil and reducing time by overheating the paste.
**Malaxation, is the action of slowly churning or mixing milled olives in a specially designed mixer for 20 to 40 minutes.
"First cold pressed" is the official definition for olive oil produced by stone mills and hydraulic presses. The paste is subjected to increasingly high pressures to extract the oil, heating the paste is not required by this methods. There is not a second pressing.
Unfiltered oil contains small particles of olive flesh. Olive Oil aficionados claim this adds additional flavour. It can causes a sediment to form at the bottom of the bottle which is the proof or the genuineness of the olive oil. Filtering the oil will reduce the content of healthy components and flavour.
A high smoke point is desirable for a cooking oil. When frying, best results occur when the oil is very hot. The food is placed into the hot oil and the natural sugars caramelise and proteins denature into a thin shell which protects the food from soaking up the oil. The outside is crisp and the interior is just cooked. The extra virgin olive oil smokes from 400 to 375 degrees F, according to it's free fatty acid content. So the Olive Oil is the best one for frying. The olive oil can also be re-used many times since it's fatty acid are mono-unsaturated. After each use strain olive oil through a filter or a double thickness of cheesecloth to remove the accumulated residue. Use common sense, don't plan on frying donuts in oil you have fried fish in.
Shelf life is very variable, depending on the olive variety, ripeness when pressed, care in processing, etc. It also depends on storage after it has left the producer, so it is hard to "guarantee" a certain lifespan. Lifespan can be as little as 3 months for a low quality late harvested olives oil, bottled in clear glass and stored in bright light on a hot stovetop with the cap unscrewed. It can be as much as 3-4 years for an early harvest, high polyphenol containing olive variety, well sealed in dark bottles then stored in a cool dark place. Also researchers have shown that oil stored in polyethylene bottles exposed to light can develop unacceptable limits of peroxide in as little as 20 days. Opened oil with headroom for exposure to air oxidizes more quickly, better to buy oil in small quantities and use it up.
While the nutritional advantages of oils depends on how the olive oil is produced (early harvesting, hand picking, first cold pressing, etc..) a more expensive oil usually has superior quality. There is no way to produce both cheap and genuine olive oil, if you look at the results of the large number of olive oil competitions you will not find any cheap mass market oil.
Bitterness and a burning are considered desirable traits and a sign of a good olive oil. As the olive oil ages over the next 6 months some of the burn will mellow out. So this is usually a sign of a fresher oil.
It's difficult to determinate the exact freezing temperature of the olive oil because it is very variable depending on the olive variety and ripeness of the olive at processing. Olive oil is made up of hundreds of chemicals many of which change with every pressing, olives has also waxes on their epidermis to protect them. So a genuine unfiltered olive oil will clump and form needle-like crystals during the winter when oil is exposed to cold temperatures during transport as the longer chain fats and waxes in the oil congeal. May also appears some clouds or white sediment which the consumer may fear represents spoilage or reduce the olive oil quality, but chilling or freezing olive oil does no harm and the oil will return to its normal consistency when warmed back to room temperature. Place it in the kitchen for a couple of days in order to heat it gently, don't try to heat it in any way (hair dryers, heating fans, etc...). Than shake it and it'll go back to the regular fantastic olive oil you know since always. In fact there are some people that are used to keep it into the refrigerator (not the best way to preserve it by the way).
When olive oil is too old and has oxidized, it is usually rancid. Oil doesn't suddenly go rancid, it slowly becomes more oxidized and as it does, the flavour suffers. All oils go rancid with heat, light and exposure to oxygen. Olive oil with low acidity and high antioxidants last longer on the shelf and tend to oxidize more slowly at high frying temperatures. Extra Virgin Olive oil by definition has nothing added, high antioxidants and low acidity. Most seed oils such as corn, canola and sunflower are inedible and unusable unless they are refined to remove acidity and have artificial antioxidants added to extend shelf life. Even though Extra virgin olive oil are stable, it will go rancid if kept in a hot place in the light. Best storage is in a cool, dark, airtight container. Oil will go rancid much quicker once heated and exposed to air than in a sealed bottle.