By Harold McGee
The fact that virgin olive oils are unrefined has both desirable and undesirable consequences. Of course the beautiful color and rich flavor are great assets. The oils also contain significant quantities of antioxidant substances—phenolic compounds, carotenoids, and tocopherols (vitamin E and relatives)—which make them more resistant than other oils to damage by oxygen in the air. However, the same chlorophyll that colors them also makes them especially vulnerable to damage by light, whose energy the chlorophyll is designed to collect. To prevent “photooxidation” and the development of stale, harsh aromas, olive oil is best stored in the dark—in opaque cans, for example—and in cool conditions, which slow all chemical reactions.