California's burgeoning olive oil producers are counting on a newly enacted state labeling law to persuade more consumers that American brands are more virginal than their imported rivals.

The measure, signed into law on Friday by Governor Jerry Brown, tightens the definitions of various calibers of olive oil, such as virgin and extra virgin, to conform with standards recently adopted by the Department of Agriculture.

Supporters of the bill say overseas labeling enforcement has slipped to the point where the overwhelming majority of imported extra virgin olive oil on supermarket shelves is actually a lower-grade product.

The aim of the new law is to help persuade California shoppers to reject imported olive oil touted as extra virgin in favor of domestic brands that are more honestly labeled, and more than likely made from olives grown in-state.

We spend a lot of money for imported extra-virgin olive oil that in many cases isn't extra virgin, when we produce actual extra-virgin olive oil ourselves, said state Senator Lois Wolk, a Democrat who sponsored the labeling measure.

In 2010 studies, University of California at Davis and Australian researchers found that of the five best-selling imported extra virgin olive oils 73 percent of bottles tested failed to meet International Olive Council standards for extra virgin.

To California's expanding olive oil industry, what extra virgin means is a big deal. The state's extra virgin is unable to compete against lower-priced and sometimes lesser quality imports claiming to be extra virgin.

A tighter definition of olive oil grades is aimed at preventing that.

Each year, more California growers enter the marketplace. The amount of California farmland devoted to olives raised for oil has increased from 6,000 acres in 2004 to 30,000 acres today.

Given its Mediterranean-like climate, California accounts for 99.5 percent of U.S. domestic olive oil production. It ranks about 20th worldwide.

Still, roughly 80 percent of all categories of olive oil are made in the European Union. While labeling standards there are comparable to the USDA's, enforcement has been lax, allowing for adulteration and labeling abuses, critics say.

The volume of olive oil consumed by Americans has jumped ten-fold during the past 30 years, from 8 million gallons to 80 million gallons annually.

One of the fastest-growing production crops is olives. They're being planted the way they were planting vineyards 10 years ago, said Wolk, whose kitchen contains bottles of olive oil made in her northern California district.

The good stuff tastes different. More flavorful. Full-bodied.