I mentioned in previous posts that olive oil when is exposed to light and heat, it becomes rancid. When you are buying olive oil, you should follow some very important rules, to ensure that you are buying a good quality product.
Make sure that you are buying olive oil in glass bottles (preferably in dark glass). The dark glass will protect from oxidation that is caused from exposure to the light. This “liquid gold” is very sensitive to light and temperature.
Place the oil in a cool place, away from heat. Light and heat will spoil the oil and will minimize its nutritional value.
There are many different grades of olive oil. Personally I recommend “cold pressed” extra virgin olive oil, because its process and acidity levels are very minimal, it is very high in phyto-nutrients, antioxidant phenols, carotenoids, chlorophyll, vitamin E and has a distinct and delicate taste.
“Cold press” is a term that should be on the label. It means that the heating that was used to process the olives, was minimal.
At the University of Leida in Spain, a research was conducted and reported at the Food Chemistry and the Journal of Agriculture, that the levels of phyto-nutrients, antioxidant phenols, chlorophyll, carotenoids, had dropped considerably, and the vitamin E had dropped completely, after the oil was stored for 12 months, even under the best conditions.
Another research conducted at the University of Bari in Italy, confirmed that light destroys the antioxidants in the olive oil.
Olive oil stored under supermarket light, loses about 50% of its vitamin E.
I buy my olive oil online. I know the oil is stored in boxes in a warehouse and has never been exposed to light or heat. When I get it at home, I transfer some in a stainless steel container for olive oil (for a few days use), and the rest gets stored in a cool dark place. I usually buy about six months supply.