Whether you like it green and grassy or butter-churn yellow, chances are you don't know quite as much about olive oil as you think you do. More than just a dip for bread or tasteless oil for heart-healthy sauteeing, true olive oil has as much depth, flavor and character as a fine wine. And can cost you just as much.

Sonoma County and neighboring Marin, Mendocino and Napa are at the heart of an artisan olive oil renaissance that goes back to the early 1990s. Inspired by the robust, peppery, fresh flavors of Tuscan olive oil, a handful of producers -- among them SoCo's own Bruce Cohn, Deborah Rogers, Ed Stolman, Ridgley Evers and Colleen McGlynn -- began producing award-winning small-production oils that tasted more like Italy and less like the bland, flavorless imported oils being dumped on the American market.

"There's fat and there's flavor," says DaVero Olive Oil's Ridgely Evers, one of Sonoma County's most outspoken advocates for buying fresh, local, extra-virgin olive oil. According to Evers, as well as UC Davis olive expert Paul Vossen, most of the cheap, imported olive oil on grocery shelves is old, substandard stuff.

"A little rancidity is normal. But olive oil just doesn't get better with time. You need to get it fresh to capture the essence and flavor," Vossen said.

Those flavors include things like green apple, green beans, grass, hay, butter, nettles, green banana or green tea. They shouldn't include flavors (or smells) like varnish, oil-based paint or old walnuts -- signs of rancidity. Extra-virgin simply means the oil is of the highest grade. Look for a certification on the bottle from the California Olive Oil Council.

Want to know how to get the good stuff? Go right to the source and be prepared to pay a pretty penny -- upwards of $20-$30 a bottle. This isn't cooking oil. Instead, use these high-quality oils for dipping, light dressings and finishing oils for meats and fish -- where you can truly appreciate their flavor. Save the cheap stuff for searing, frying or sauteeing.

The best time of year to get olive oil is straight from the presses in November/December (when it's called Olio Nuovo) or after it has settled, usually around March. Store in a cool, dark place for about a year. After that, treat yourself to a new bottle.

Where to go

The Olive Press: Located inside Jacuzzi Winery (and just down the street from the dip-and-nibble mecca, Viansa winery in Sonoma), it's easy to dismiss the raffia-ribboned, sample-bar charm of the Olive Press as tourist fodder. Which would be a mistake. Co-owner Deborah Rogers is one of the most lauded and respected olive oil producers in California and the Press is a bonanza of hard-to-find, small-production local oils made on-site.

Two of the earliest champions of Northern California's olive oil boom, Rogers and business partner Ed Stolman, recently relocated their milling operation from Glenn Ellen to the higher-trafficked Carneros region. Rogers continues to make her private label, Marquessa, a bold blend of old and new world olives and Stolman's, Lunigiana, has taken top prizes in Italy and Spain -- a bold oil with plenty of bitterness and throat-tickling pepper.

For olive oil enthusiasts, Rogers also bottles a handful of varietal olive oils, from the grassy, fruity Sevillano (one of the most approachable dipping oils we tasted), to the lusty Koroneiki, a Greek olive variety under the Olive Press label. Best-sellers, however, are her growing lineup of flavored oils -- clementine, Meyer lemon, jalape? and most recently, lime. Citrus zest is crushed along with the olives to infuse, rather than just flavor, the finished product. You can taste many of Rogers' oils, as well as offerings from her clients, including microproducers Beltane Ranch, Stone Edge and Napa's Cypress Hill. Go to the Olive Press in Sonoma (24724 Arnold Drive, Sonoma, 800-965-4839) or the Oxbow Public Market (644 First St., Napa).

DaVero Olive Oil: Ridgley Evers has some strong opinions about olive oil, which he's never shy about sharing. One of a handful of olive growers behind Sonoma County's artisan oil boom, Evers and his wife, chef Colleen McGlynn, have made a career out of meticulously understanding the nuances of flavor, balance and timing when it comes to their oils.

The 4,500 trees on their Dry Creek property trace their heritage from a handful of saplings they imported from Lucca, Italy (a Tuscan region with weather much like Sonoma County). McGlynn and Evers, who counts chef Mario Batali among his admirers, can be found most weekends selling their oil at local farm markets and are in the midst of converting their estate to biodynamic farming principles. Their flagship EVOO has all the qualities of a great California olive oil -- fresh grassiness, a mild bitterness and a sneaky pungency. "Three coughs are a compliment," says Evers. Tours, classes and tasting: davero.com or 431-8000.

Terra Bella Vista Olive Oil Co.: A true mom-and-pop venture, this growing Bennett Valley orchard is a labor of love for Doug and Judi Webb. The couple have gone from harvesting just a few hundred pounds of olives in 2004 to 5,300 pounds in 2007. Each November they gather friends and family to assist with the harvest and immediately head for the press, Olivinio in Hopland (also used by DaVero). Tours, by appointment, 586-3777 or tbvevoliveoil.com.

Stella Cadente Olive Oil: A Mendocino favorite, Stella's basil olive oil recently won big love at the Fancy Food Show in San Francisco, put on by the National Association for the Specialty Food Trade every year in January. Though herb-flavored oils sometimes just mask low-quality oil, Stella's bright, fresh-basil flavor doesn't overpower the flavors of the oil. (800) 305-1288 or stellacadente.com.

Skipstone Ranch: Small-production Alexander Valley olive oil with a very fresh, green flavor. Fahri Diner and Jill Layman, who own the property mainly devoted to steep hillside vineyards, take advantage of 550 Manzanillo olive trees planted there. Available online at skipstoneranch.com.

BR Cohn: Winemaker Bruce Cohn's grove of French Picholine olives trees, planted in the late 1800s, inspire the soft, buttery flavors of their Sonoma Estate extra virgin olive oil. Available at the winery, 15000 Sonoma Highway, Glen Ellen, (800) 330-4064 or online: brcohnoliveoil.com.

Dry Creek Olive Company: This recent entrant into the local olive oil scene has impressed even the toughest critics with their approachable and well-made oils. One of the few mills with a granite press (the large circular stone wheels that crush the fruit), Dry Creek mixes olives from local growers, their own estate and does several infused citrus oils. Best bets are the cheeky Healdsburg Blend and refined blood orange and Meyer lemon oils. Want a taste of the harvest? Olio Nuovo is a green, grassy and fruity blend. Tasting room and mill at 4791 Dry Creek Road, Healdsburg, 431-7200.

Dry Creek also mills for a number of small, local producers, including El Poeta (available at the Dry Creek General Store), a strong, earthy, lusty oil that just about knocked our socks off.

McEvoy Ranch: McEvoy has become the gold standard for Northern California olive oil making. Even competitive olive oil producers get a little wistful when describing the painstakingly designed property and state-of-the-art Italian equipment used to mill their mild yet complex extra virgin olive oil -- the one and only oil they produce. The ranch, based in Marin county and owned by newspaper heiress Nan McEvoy, boasts nearly 18,000 trees over 550 acres. It is a private residence, but will be open for tours on Father's Day weekend and occasional dates throughout the summer. Reservations are required. 5935 Red Hill Road, Petaluma. More details at mcevoyranch.com or 778-2307.

Want to learn more? The "Beyond Extra Virgin" Conference will be held at the CIA Greystone and UC Davis from June 21-23, the largest conference on olive oil quality ever held in North America. The Culinary Institute of America at Greystone is located at 2555 Main St., St. Helena. More details: www.cooc.com/events.html