I recently purchased a bottle of extra virgin olive oil. It was a deep green-gold color, as usual. However, it has begun to lighten. The oil is still clear, not cloudy, and still good. It has not been exposed to direct light, or even much indoor lighting.
I have heard that this can happen, but I've also heard that only vegetable oil might lighten.
Oil coming out of the press is sometimes a brilliant emerald green. Chlorophyll and carotenoid pigments create the color. Olive oil undergoes many changes after production. Oxidation from the air in the bottle, auto-oxidation and exposure to heat and light drive these changes. Oil usually lightens in color as pigments are used up by oxidation. New olive oil is sometimes too harsh to use; producers will wait months before releasing their new crop to smooth out the bitter and harsh flavors. As the oil in the bottle ages it will lighten in color and the flavor can continue to mellow. In 1 to 3 years the oil will eventually become rancid. Heat and light speed this up but unless frozen, these changes inevitably occur even in well stored olive oil.
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