WASHINGTON — I went looking for extra tomatoes at the farmers market this weekend (my backyard crop is not up to par this year), and I got another "extra" as well: a brief refresher course about extra-virgin olive oil.

Thanks to my farmers market tutor, Keith Voight, I can now pass this true-false quiz. Can you? (Answers below.)

1. The designation "extra-virgin" means something different in the United States than it does in Italy, Spain, France or Israel.

2. A real extra-virgin olive oil has no defects in taste or odor and a very low level of acidity.

3. Olives pressed for extra-virgin oil can be picked early or late in the fall-to-winter season.

Voight owns All Things Olive, an online retailer based in Kensington, Md. He has sold exclusively Californian extra-virgin olive oils for five years. He also spends a fair amount of time educating others about the oil's particular characteristics.

At its essence, real extra-virgin olive oil is pure, raw, unprocessed and unrefined, with no defects in taste or odor and with less acidity (oleic acid) than virgin or pure olive oils. And it has to be extracted from the olives within a day of when they are picked, to keep that acidity low.

Voight carries extra-virgin olive oils that are mild and delicate; fragrant and fruity; leafy and grassy; olive-y and peppery. Their flavor depends in part on at what point the olives were picked during their October-January harvest.

It's his contention that most Americans have never really tasted extra-virgin olive oil because of its relatively low yield and the extra care it takes to produce it properly. His line is all-Californian because the state has its own olive oil control board (look for state-made oils with a COOC seal) and takes its olive oil production seriously, with a study center at UC-Davis and various organizations aimed at standardizing and improving quality. Voight does not think Californian extra-virgin olive oils are on a par with some of Europe's finest — yet, anyway. But he does prefer them to imported oils because freshness is key, and that advantage goes to the extra-virgin olive oils made and sold in the Golden State.

A tasting of his selections led me to choose the mild, late-harvest Apollo Mistral, made in northeast California. It is soft and buttery, good for white wine dishes, salads and seafood, he says. Last night I drizzled it into orzo with medallions of lobster, sauteed corn, scallions and tomatoes. Because it's in a dark bottle and only 375 ml, it will remain unaffected by sunlight (which can break it down) and I'll most likely use it up fairly quickly.

If I wish to use it instead of butter in recipes, I'll try this handy dandy chart I found at www.OliveOilSource.com:

BUTTER VS. OLIVE OIL