A good bottle of olive oil is a requirement for just about every kitchen. From drizzling over vegetables or meats to crafting salad dressings and bread dips, a little olive oil can make your cooking sing. But how much do you need to spend for a quality olive oil, and how long will it last once opened? Is extra-virgin olive oil all that it purports to be?

We get these kinds of olive oil-related questions often at The Bee's Food and Wine section. To help sort through the answers, we consulted two local olive oil experts: Dan Flynn, executive director at the University of California, Davis, Olive Oil Center; and Darrell Corti, the epicure and grocer who's an internationally recognized expert on olive oil and a frequent olive oil competition judge.

The olive harvest typically begins in early November, and more consumers are turning to olive oil for their culinary needs. According to Flynn, about 2 million gallons of olive oil are expected to be produced statewide in 2012 – about double the amount from the previous year. Like wine, sorting through rows of olive oils at the store sometimes feels like a guessing game. Quality can range greatly, as will their flavor profiles, which span from fairly neutral to so pungent that the spiciness can make you cough.

"The quality of olive oils are based on the variety (of olive used), the time of their picking and the type of extraction used," said Corti. "All oils have a flavor character that's pungent and bitter. That's the normal flavor component of an olive. You want the oil to retain its bitterness and pungency."

So, what's the best way to care for these oils, and what should you look for when shopping? Here's some olive oil guidance from Flynn and Corti:

Olive oil and oxidation: How long will it keep?

Let's say there's a great price on a gallon of olive oil that seems hard to pass up. Well, unless you plan to cook a lot with olive oil and use it fairly fast, it's best to buy these oils in smaller amounts.

The best olive oil is the freshest olive oil, and as with wine, oxygen is an enemy. Once a bottle is opened and oxygen gets introduced in the bottle, that's the start of an oxidation process that leads to declines in flavor and aroma. Olive oils contain fatty acids that can help fight off oxidation, but in the end, oxygen will always win. Plan on using up that bottle within weeks.

"As you use the oil, you're going to add some head space into the bottle, and that's how oil gets oxidized," said Flynn. "I try and use an oil as quickly as I can. Six to eight weeks can be good. If you can't use it in that time, you're maybe buying too big a container."

Unopened bottles of olive oil can last up to two years if stored properly. Olive oils aren't meant to age like wine, and their flavors can soften with extended time in the bottle. To keep your olive oils the freshest they can be, heed this advice:

"Keep them in a cool, dark place – and buy them often," said Corti.

Heed the harvest date stamped on the bottle

This assumes your olive oil bottle comes stamped with a harvest date. If not, that's a key indicator that your oil likely isn't of the best quality. Some olive oils might have a "best by" date instead, but harvest date will be a better indicator of how fresh your oil may be.

"A 'best by' date is important as well, but we've found in some studies that a lot of that oil has already gone south," said Flynn. "They had some rancid and off flavors, but were within the 'best by' date. Look for the harvest date. Every olive oil, no matter how good it starts out, is going to decline. Retailers are becoming more aware of this importance."

Assessing 'extra-virgin'

The term "extra-virgin" is supposed to connote the utmost in olive oil purity. By definition, an extra-virgin olive oil must be free of defects, while exhibiting a certain measure of fruitiness. The oil must also be extracted solely by mechanical means, and no solvents may be used during processing, among other factors. Such standards are set by the International Olive Council, the United States Department of Agriculture and other bodies. Tasting panels also are used to determine if an olive oil is indeed extra-virgin.

Plenty of controversy has surrounded "extra-virgin." A UC Davis Olive Center study found that 69 percent of imported oils in the American marketplace listed as "extra-virgin" didn't meet set standards once sampled by a UC Davis and Australian research team. Ten percent of California olive oils didn't meet the extra- virgin test. The study found defects caused by oxidation, processing flaws and adulteration with cheaper oils.

That's to say, don't buy an olive oil by the term "extra-virgin" alone.

"Not all extra-virgin olive oils are created equally," said Flynn. "It is something to look out for, but people need to be smart. You can have a bland oil that will pass that test. Also, if you find an oil that's made from multiple countries, there's not a good track record from tests that it will be very good."

Don't judge an oil by its color

Olive oils come in many shades, from golden yellows to deep, grassy green. But unlike wine, in which evaluating color is a key part of any analysis, there's no connection between the lightness or darkness of an oil and the strength of its flavor. In formal olive oil tastings, the oils are placed in colored glasses – often cobalt blue – so a taster's sensory analysis isn't prejudiced by the oil's color.

"The color of olive oil has nothing to do with the taste of the oil," said Corti, in a firm tone. "What you do want to pay attention to is its clarity."

That's to say, even light-colored olive oils can boast intense flavors.

"We did a tasting where we had a super-fresh oil from Chile, a store-bought import and a California arbequina produced in November. The Chilean was the lightest, but because it was so new it was the one with the biggest, robust flavor."

You don't have to splurge to get a quality olive oil

Olive oils can be found across the price spectrum, from a $4 bottle of Star at the supermarket to imports and other meticulously crafted oils that cost upward of $30. Still, price alone doesn't necessarily determine an oil's quality. In a recent test of 23 olive oils by Consumer Reports, only two olive oils were rated "excellent": McEvoy Ranch olive oil ($22) and Trader Joe's California Estate olive oil ($6).

"That's a good indicator that there's good oils across the price range," said Flynn. "If people do pop for an expensive bottle, they should still use it up. Don't save it for a special occasion. It will be best right at the outset."

"You need to be considerate of the harvest date and how old that oil is," said Flynn. "I've been to a lot of shops with $30 oils, and those oils were a couple years old."

On cooking with olive oil

Unless you have money to burn, using high-quality olive oil for cooking and frying somewhat defeats their purpose. These oils generally have pronounced flavor profiles, and heat will just strip away much of their taste. They're best used for drizzling over vegetables or carpaccio, or as the basis for salad dressings and dips for bread.

"You typically want to appreciate the full flavor of the olive oil," said Flynn. "I freely put the value California oils in a pan. They're cheap enough and can be used for basically everything."

Still, a high quality olive oil for frying or sautéing can generate pleasing results. Even if their flavor profiles might be forsaken, these olive oils can hold up well to high-heat cooking.

"Conventional wisdom says olive oil has a low smoke point," said Flynn. "That's true of lower-quality oils, but a decent-quality olive oil will take you up to 400 degrees with no problem. You can deep fry with an extra-virgin olive oil if you want to."

The last word on freshness

"One thing people don't really think about with olive oil because it's a natural product, freshness is really important," said Flynn. "In a week or two, you can see how the flavor of the oil changes. Think of it more like a fresh product, like milk or orange juice. That'll give people a different view of how long to keep it and what it should taste like."

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