No, this is not a post declaring olive oil bad or even ugly! Olive oil is an awesome source of healthy fats, full of antioxidants and anti-inflammatory properties! Even more impressive; a good quality olive oil has a substance called oleocanthal which has the same pharmacological effects as ibuprofen. There are, however, some important tidbits that many people are not aware of in terms of keeping or maintaining those health benefits.
1. Fresher Is Better:
Choose an olive oil that has a packaging date that's less than a year old and use it within a year's time. The better quality olive oils will always have that stamped date.
2. Best To Worst:
Extra Virgin Olive Oil - the Mercedes of olive oils
Virgin Olive Oil - by definition, this oil has not gone through any processing
Light Olive Oil - not lighter in caloric value, just lacks flavor (what's the point?!)
Refined Olive Oil - low quality; refined by charcoal or chemical method (say again?!)
Blended Olive Oil - a blend of low quality olive oil PLUS other vegetable oils (just avoid that mess!)
Here's where trial and error come to play because the best method of choosing an olive oil is by using your senses - smell and taste. For obvious reasons, most grocers will not allow you to open several bottles of olive oil simply to smell and taste. However, if you go to local Italian markets, they will often times have samples sitting out for you to taste and smell. If you live near Salt Lake City, check out Caputo's Deli (they have it ALL!). The smell should be of...well...olives! Fresh and clean. The taste should also be of - yep - olives! Light and tasty, not greasy. If there's a metallic taste, it's probably gone rancid. If you get your olive oil from the local market, more than likely you'll be in good shape in terms of quality and certainly selection. Purchasing imported olive oil is not necessarily a guarantee of quality/freshness. It has had to travel many miles and spent much time in storage, making the oil less flavorful. Trying some domestic olive oils might be a smart choice!
Here is where alot of people go astray. Olive oil can and will oxidize when exposed to heat and light (its greatest enemies!). Store in a cool dark place. If at all possible, purchase your oil in a dark bottle or, if buying in bulk, in a can rather than clear bottles. Extra virgin is the least stable, so try keeping it in a cooler location (not near the stove!). You can store in the refrigerator, but you'll lose the delicate flavor.
5. To Heat Or Not To Heat:
It is true that olive oil is unstable when exposed to heat. The oil will oxidize. The higher quality oils will tend to have higher levels of antioxidants and phenolics which means less oxidative damage compared to lower quality olive oils, but the oxidative properties still exist. In order to minimize these oxidative damages, it's best to purchase high quality olive oil, store in a cook, dark location and use with lower heating temps.