Lidia Bastianich is many things: a star TV chef, a restaurateur extraordinaire (Felidia and Becco in New York City, Lidia's Kansas City and Lidia's Pittsburgh) and a celebrated author. The purpose behind everything she does is to introduce American cooks to the magnificence of the Italian table. Here, she tells Food & Wine magazine the five things every cook needs to know about buying and using olive oil, one of the most prized ingredients in an Italian pantry. As she says, "Olive oil is a lesson unto itself, and I'm going to give you a quick one."

1. Use the right grade of oil

All olive oil is graded by the amount of oleic acid it has—the less acidity in the oil, the smoother and more aromatic it is. Extra-virgin olive oil, the highest and most expensive grade, contains less than 1 percent oleic acid; virgin oil has less than 2 percent; regular oil has up to 3.3 percent. I use extra-virgin for drizzling over salads or soups or for cooking something over gentle heat. If I make a braise, I start with a virgin or regular olive oil to brown the meat, then discard it and add more flavorful extra-virgin for sautéing the onions.

2. Read the label

On bottle labels, you'll often see the words "first pressing" or "cold pressing" because they are very important. The "first pressing" of the olives to release the oil is the gentlest. "Cold pressing" means that the oil stays cool while it's extracted from the olives; pressing olives while they're hot yields more oil, but destroys the flavor.

3. Learn the difference between Italian oils

There are more than a thousand different kinds of olives, but only a few varieties are used in Italy to make olive oil. In each region, some varieties grow better than others, and that helps determine the kind of flavor the oil will have. The olives that grow very well in Tuscany yield oils with a peppery finish. The olives that grow in the cooler climate of Liguria make oils that are lighter, buttery and more fruity. If you go down to Puglia, where it's hot and the soil has lots of clay, the oils are very grassy and rich.

4. Taste the oils, then trust your palate

Before you buy a big bottle of expensive, boutique olive oil, make sure you taste it. If you can, buy three small bottles of different oils—perhaps one from Liguria, one from Tuscany and one from Sicily. Sit down and taste them together. Really taste them, noting the distinctive flavors and differences in viscosity (how it feels in your mouth). Take a bite of a green apple to cleanse your palate. People sometimes don't feel secure in their preferences, but if you like an oil, then it's good! Trust your mouth, and then, like anything else, you'll develop an expertise with practice. I like to have the peppery Tuscan oils with steak; if I'm doing a risotto with herbs, I'll use a Ligurian oil. Bigger, "fatter" oils will overpower lighter food, much like a big red wine would.

5. Store oils properly

Another important thing to know about olive oil is that it is molecularly unstable, which means it will oxidize and become rancid. The oil should have minimal contact with oxygen, so if you pay a lot for an olive oil, use it quickly or pour it into smaller bottles to preserve freshness; keep the bottles as full as possible and store them in a dark, cool place. You can store the oil in the refrigerator but it will solidify, so bring it to room temperature before using. Your nose will tell you if an oil has gone off. And if not your nose, then your palate. The oil will smell musty and taste rancid, with harsh acidity.

Updated July 2010