Capers pack big flavor in a tiny package. These little spheres are the flower buds of a prickly shrub that grows all over the Mediterranean. Eaten raw, capers are unpalatably bitter, but once cured in a vinegar brine or in salt, they develop an intense flavor that is all at once salty, sour, herbal, and slightly medicinal. If the buds are allowed to blossom and go to seed, they become caper berries, which are also packed in brine and can be added to salads or eaten out of hand like olives.
Capers come vinegar-brined or salt-packed. Brined capers have the advantage of an almost indefinite shelf life, but the vinegar sharpens their flavor. Salted capers have a pure flavor, but they don't last as long because the salt eventually pulls out all their moisture. Capers taste especially good with fish and other foods that tend to be oily or rich.
Capers come in a range of sizes. The smallest size (nonpareil) is said by some to be the best; others prefer larger capers for their bolder, more interesting flavor. What you choose is a matter of personal taste and what you can find at your market. For salt-packed capers, look for clean white salt; yellowing salt is a sign of age.
Rinse brined capers before using. Salt-packed capers are too salty to be eaten straight from the jar; soak them in cool water for about 15 minutes and rinse in several changes of water. If the capers are large, you can chop them roughly unless you want a big burst of caper flavor. For an unusual garnish or salad addition, pat capers dry and then lightly fry them in a little olive oil. They'll get crisp and open up like the little flowers they are.
All capers should be refrigerated after opening.