Because olive oil consists of the more stable monounsaturated fatty acids, it can be safely stored at room temperature for several months. It is the only non-processed oil available on supermarket shelves that does not deteriorate quickly while retaining most of its original nutritive value. It is virtually impossible to find oils that have been commercially pressed without heat, but the one exception is olive oil (the other is a special brand of peanut oil).
Production must be a rapid procedure that begins with the fruit being brought directly to the extraction plant after collection. Because it is a fruit, it cannot be stored for any length of time, nor can it be dried. The oil must be extracted as soon as possible before the acid content increases, impairing quality.
The olives are then separated from any foreign material, washed, and ground to a fine paste. Oil extraction from the paste can be done either by hydraulic press or continuous centrifuge. During the extraction, three fractions are separated from the paste: oil, waste water, and the husks or residue. The husks are dried and the remaining oil extracted with the addition of solvent. In this way, more than one type of oil is obtained, and is the oil used in the lower grades of olive oil.
Extra Virgin Olive Oil means the highest quality involving strict guidelines and is extracted from the first pressing of olives. It has full flavor and aroma and contains most of the beneficial substances that are naturally present in olives. The overall quality and nutritive value is superior to either the virgin or refined olive oils.
Virgin Olive Oil is obtained by pressure or centrifuge with a free fatty acid level below 4%. This oil comes from the first or second pressing and is of a somewhat lower quality.
Refined Olive Oil is obtained with a solvent extracting it from the husks and mixed with the originally pressed oil. It has a high free fatty acid content and an unacceptable flavor. Therefore, it must be neutralized to decrease the free fatty acid content and blended with a good quality virgin olive oil to produce a more acceptable flavor. Pure or light olive oils come from the second pressing and, since this oil is higher in solid particles, it must undergo further refining which lowers its nutrative quality.
Other compounds found in olive oil are:
1) Palmitic acid, which can raise cholesterol levels, but olive oil seems to protect rather than damage.
2) Stearic acid, which neither raises or lowers cholesterol.
3) Small amounts of lecithin.
4) Beta carotene and Vitamin E, known antioxidants.
5) Chlorophyll, known to be a good source of magnesium.
6) Squalene, a precursor of phytosterols, which protects against cholesterol absorption from foods.
7) Modified sterols known as triterpenic substances, which seem to benefit the cardiovascular system and have healing and anti-inflammatory properties. Triterpenic acids (oleanolic and maslinic) found only in olive oil, stimulate pancreatic enzymes.
8) Polyphenols, with one such being oleoeuropein, known to lower blood pressure.
9) Plus more than 100 other compounds that give flavor and aroma that have been identified but not studied.
Some minor components of olive oil that can have major effects:
1) Beta-sitosterol lowers high cholesterol levels.
2) Caffeic and gallic acids stimulate bile flow. Gallic acid also inhibits lactic dehydrogenase activity, which is a sign of liver malfunction.
3) Phenolic compounds protect against peroxidation of fatty acids and cholesterol.
4) 2-phenylethanol, present in many unrefined oils, stimulates production of fat-digesting enzymes in the pancreas.
5) Cycloartenol, which is stored in the liver, lowers the amount of circulating cholesterol and increases bile excretion.
6) A combination of Triterpenic acids and 2-phenylethanol slows down cholesterol digestion and its absorption from foods.