Two pear-shaped avocado varieties dominate supermarket produce sections. The Hass has a buttery flesh and a pebbly skin that darkens from green to purple-black as it ripens. It constitutes more than three-quarters of the avocado market, and traces its lineage to a tree planted in the 1920s by mail carrier and horticulture hobbyist Rudolph Hass in his front yard in La Habra Heights, Calif. Less widely available is the smoother, paler Fuerte avocado; compared with the Hass, the flesh remains firmer and not as rich.
An avocado is ripe when it yields to gentle finger pressure. Avoid avocados that feel mushy or appear shriveled. Ripe avocados can be stored at room temperature for up to two days, or refrigerated for three days.
Unripe avocados should be stored in a warm, dark place. To accelerate ripening, place the avocado in a brown paper bag (at room temperature) with an apple, banana or kiwi fruit; all emit ethylene gas, which triggers ripening.
When exposed to air, an avocado's flesh quickly turns brown; cut just before serving. To store a cut avocado, wrap it in plastic wrap (gently pressing and smoothing the wrap right onto the fruit's cut surface to seal out air) and refrigerate.