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  • Author or Editor: Paul Vossen x
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The true origin of the olive is not known but is speculated to be Syria or possibly sub-Saharan Africa. For more than 6000 years, the cultivated olive has developed alongside Mediterranean civilizations and is now commercially produced on more than 23 million acres (9.4 million ha) in the Mediterranean basin. New plantings also exist in California, Chile, Argentina, South Africa, and Australia. Various nonscientific selection processes created a multitude of different cultivars. Many villages in Europe, the Middle East, and North Africa feature distinct varieties. However, it is also common to see the same cultivars with different names and, in some cases, different cultivars with the same name. This is currently being sorted out with DNA identification. The olive tree requires some chilling; tolerates hot, dry conditions; does not like moisture during bloom, and actually produces better with some stress. As a result, olives were traditionally relegated to lands where little else would survive. For thousands of years olives were grown primarily for lamp oil, with little regard for culinary flavor. World production of table olives is now about 1.5 million t/year. The “California Style” black table olive is virtually unknown outside the United States, and this very mild-flavored olive is largely used on pizzas. Elsewhere, table olive recipes are as varied as the villages in the Mediterranean region. Oil styles are also varied, and most olive fruit (≈16 million t/year) is processed into oil. There are about 19 classic styles of olive oil produced in the world, primarily based on specific varieties grown in different regions. In some cases oils are made with a blend of regional varieties. Defective olive oil is common worldwide. The author discusses six of the world's most influential olive oil varieties ‘Picual’, ‘Coratina’, ‘Koroneiki’, ‘Arbequina’, ‘Frantoio’, and ‘Leccino’; covers some horticultural history of oil olive cultivation and processing; and describes the most current trends toward superhigh-density plantings and automated continuous oil processing.

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A comparative study was conducted to evaluate the influence of seven different levels of irrigation applied to `Arbequina I-18' olive (Olea europaea L.) trees grown in a super-high-density orchard (1,656 trees/ha) in the Sacramento Valley of California. Water was applied differentially by drip irrigation at rates of 15%, 25%, 40%, 57%, 71%, 89%, and 107% evapotranspiration (ETc) in 2002, and 28%, 33%, 55%, 74%, 93%, 117%, and 140% ETc in 2003. Each treatment was replicated three times. Olives were harvested on two different dates each year from each of 21 plots. Three of four harvest dates showed a decrease in maturity index with increasing irrigation levels. Oils were made from olive samples collected from each plot and analyzed for oil quality parameters. Total polyphenol levels and oxidative stability decreased as the trees received more water, especially for the three lowest irrigation treatment levels in 2002, but few differences were noted between treatments in 2003 when all the trees were irrigated more heavily. Average oxidative stability was correlated very closely with total polyphenol content with r 2 = 0.98 in 2002 and 0.94 in 2003. In 2002, free fatty acid levels increased and peroxide levels were unchanged, but in 2003, free fatty acid levels were unchanged and peroxide levels decreased in treatments receiving more water. Saturated fatty acids did not significantly change in 2002, due to tree irrigation level. The mono-unsaturated fatty acid levels and oleic–linoleic relationship declined while poly-unsaturated fatty acid levels increased in 2002 with increased irrigation. In 2003, there was no notable difference in the ratio of mono to poly unsaturated fatty acid levels. The individual fatty acid most consistently affected by more irrigation water was stearic, which decreased in both years. Total sterol content (mg·kg–1), percentages of cholesterol and erythrodiol were significantly influenced by tree irrigation levels, but increased in one year and either decreased or were unchanged the next. Oil sensory properties of fruitiness, bitterness, and pungency all declined in oils made from trees receiving more water. The lowest irrigation levels produced oils that were characterized by excessive bitterness, very high pungency, and woody, herbaceous flavors. Intermediate irrigation levels (33% to 40% ETc) produced oils with balance, complexity, and characteristic artichoke, grass, green apple, and some ripe fruit flavors. Higher irrigation levels lowered oil extractability and produced relatively bland oils with significantly less fruitiness and almost no bitterness or pungency.

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