Here is advice from Dan Flynn, executive director of the UC-Davis Olive Center when buying olive oil:
Look for a harvest date on the label. Freshness is important for quality and nutrition. Some retailers are becoming more savvy about this.
Color is not an indicator of freshness. Some people think a strong green tint means better quality, but some olive varieties are just greener than others. Some high-quality olive oils are a golden color.
Buy olive oil in a container that protects the oil from light. That could be dark glass or a tin.
People need to taste truly fresh oil. I believe most people are used to an oil that is not fresh, and that’s what they think it should taste like. There’s a high-quality product available at the same price. Extra virgin olive oil has a special flavor and freshness. Once people taste fresh extra virgin olive oil, they’ll want to continue choosing it.
Olive oil should smell fruity and taste like olives. Some describe high-quality olive oil as “grassy” or “peppery.”
For maximum nutrition, quality and flavor, ideally, the olive oil you buy should not be more than one year old. It should say “extra virgin.” It should be harvested carefully, processed quickly and minimally, stored in a cool dark environment, and opened and used without too much exposure to air.