Sensory taste panels have helped to elevate California olive oil to premium status, while new hedgerow planting systems are rapidly increasing olive acreage in the state, according to articles in the January-March 2011 issue of the University of California's California Agriculture journal.

"The next decade could see California producing a significant amount of the olive oil consumed in the United States," said UC Cooperative Extension Farm Advisor Paul Vossen, whose work has helped cultivate a unique and growing agricultural market for olive oil in California.

California Agriculture's special issue on olives and olive oil, "Growing bigger, better: Artisan olive oil comes of age," which includes peer-reviewed research articles and news coverage, can be viewed and downloaded at

Vossen was instrumental in establishing California’s first olive oil sensory-taste panel, which was certified by the International Olive Council in 2001; it was the first IOC-recognized panel in the United States. Tasters are carefully selected and continuously trained to recognize defects in extra-virgin olive oil, as well as positive flavor attributes such as fruitiness, bitterness and pungency. Many members of that original panel are now members of the UC Davis Olive Oil Taste Panel, which was recognized by the IOC in late 2010.

In addition to certifying that oils are properly labeled as "extra virgin," the taste panel provides valuable feedback to growers, helping them to fine-tune their growing practices and improve the resulting olive oils.

"From 1999 through 2004, the number of defective oils [tasted by the panel] dramatically declined from 50 percent to less than 3 percent," Vossen and co-author Alexandra Kicenik Devarenne noted in California Agriculture journal. "Due to UC research and support, and the efforts of the sensory panel volunteers, it has become a rarity to find defects in California olive oil."

At the same time, experts say that California olive oils are becoming as interesting and complex as the state’s fine wines.

"California olive oils are not just fats, but are like spices or condiments," Vossen said. "These fine oils impart delicious, subtle flavors to food."

High-density hedgerows.The vast majority of olive oil (about 98 percent) consumed in the United States is imported from Europe and other countries, but new technology is playing an important role in rapid expansion of California production.

In traditional orchards, olives are planted at about 50 trees per acre (about 30 feet apart) to allow them to reach their full, natural size. In the early 2000s, European olive growers introduced hedgerow-based systems -- very similar to those used in grapes -- for growing olive trees. "Super-high-density" hedgerows, with more than 600 trees per acre, reach full production in a shorter amount of time and allow olives to be harvested mechanically, with significant reductions in labor costs.

About 12,000 acres of olives have been planted in high-density systems in California over the past decade. Research in California Agriculture compares cultivars developed in Spain and Italy, which have Mediterranean climates like California's, for use in these modern olive hedgerows.

Just a few olive varieties have been compared for their adaptability to high-density plantings and continuous mechanical harvest," Joan Tous of the Institut de Recerca i Technologia Agroalimentaria in Catalonia, Spain, and colleagues wrote in California Agriculture journal. The researchers looked at characteristics such as growth habit, vigor, yield, maturity and oil quality in olives grown in Spain and Italy.

Olive fruit fly

Olive fruit fly.The detection in the late 1990s of the olive fruit fly, a non-native pest insect, has presented significant challenges for the California olive industry. Found now in more than 40 counties, it is here to stay.

"The olive fruit fly is a primary pest of olives worldwide and is particularly troublesome due to its multiple, overlapping generations each year," wrote Hannah Burrack, assistant professor of entomology at North Carolina State University, and co-authors in California Agriculture. "This life history makes understanding olive fruit fly phenology and infestation patterns particularly important for effective management."

Three articles in the special issue of California Agriculture discuss strategies for controlling olive fruit fly, including global exploration to find natural parasites of the fly; extensive statewide monitoring of the pest and its reproduction cycles; and the impact of Central Valley heat on fly activity and populations.

The table olive industry has zero tolerance for fruit damaged by olive fruit fly, but the olive oil industry can accept some infestation without deleterious effects on the oil's quality or taste.

"With early harvest and rapid processing, minor olive fruit fly damage can be tolerated, which can save treatment costs and reduce environmental contamination," Vossen and Kicenek Devarenne wrote in California Agriculture.