According to Tom Mueller, author of "Extra Virginity: The Sublime and Scandalous World of Olive Oil"; blogger at extravirginity.com.
Olive oil is closer to a fruit juice than to a nut or seed oil. Many fruits start to degrade as soon as they've been picked, and olives are especially susceptible, so scan the label for a harvest date -- the more recent, the better; ideally it should be within the past 12 months. Or at least look for the latest best-by date you can find. Among supermarket oils, I like the California producers Corto Olive and California Olive Ranch; both use harvesters that get the fruit off the trees and into the mill within hours.
Nearly every label lists terms like extra virgin and first cold press, which really don't mean much anymore. And while I'm all for organic, I'm not convinced that the market is being policed efficiently enough to ensure that the makers are actually meeting regulations. More important is that the oil, which is light-perishable, is packaged in tin or dark glass.
The label should say exactly where the olives were grown. Often you'll see some folksy text on the label about Italy, but in smaller print it may say that the olives came from Spain, Tunisia, or elsewhere -- it's a real grab bag. Some of the best oils are artisanal ones made in Italy, Greece, and Spain, including one of my favorites, Oleoestepa.
It's amazing how quickly olive oil shops are proliferating around the country. Ask about the types of olives in what you sample. Some, like coratina and koroneiki, produce big, pungent oils. Others, like arbequina and arbosana, tend to be milder and more buttery.
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