Olive oil is made by crushing olives to a paste. Freerun oils are those that drip from the paste. But most are extracted by pressing or spinning the paste in a centrifuge. For cold press, no heat is applied. The finest oil, extra-virgin, is often described as a first cold press and unrefined. Additional pressings, often with heat or chemicals, produce lesser-quality oils. Oils may be filtered to make them clear; however, unfiltered oils may clarify on standing.
A California olive oil must be made only with olives grown in the Golden State. If it's an estate oil, all the olives were grown on the owner's land. If the olive oil is labeled organic, the trees are chemical-free.
The label may specify when the fruit was picked. Usually, early harvest means fall to winter, late harvest winter to spring. Early oils tend to be green and taste grassy, while late oils are typically gold and buttery-tasting. The olive varieties may or may not be identified on the label.
Store olive oil airtight in a cool, dark place. Do not refrigerate.
HOW SHOULD OLIVE OIL TASTE?
The California Olive Oil Council (COOC) seal "Certified Extra Virgin" on the label means the COOC has tasted and approved the oil's quality. Approved oils rate as close to flawless as possible. Descriptions of tastes or aromas include fruity, grassy, fresh, clean, and pungent. Oils may have have a slightly bitter flavor, reminiscent of raw artichokes, but they shouldn't be harsh. Nor should they taste or smell musty, fermented, muddy, vinegary, metallic, or rancid.
Three experts ― Darrell Corti of Corti Brothers specialty food and wine merchants in Sacramento; Maggie Klein, author of Feast of the Olive: Cooking with Olives and Olive Oil and co-owner of Oliveto Cafe & Restaurant in Oakland; and Giovanna Passalacqua, a COOC-trained olive oil taster ― explain how to evaluate oils: First check for aromas, then taste (on cubes of bread). An olive oil should taste good ― a judgment anyone can make.