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Science Insight: Why the Dark Bottle?

Fine wines are bottled in dark green glass and milk bottles have been replaced by opaque cartons. The best olive oils are bottled in dark glass or in tin cans. Ever wondered why?

The short answer is that dark glass protects the oil from the deteriorating effects of light. Even a few weeks of light exposure will accelerate the aging of olive oil. We implore you to store our oil in a dark, cool cabinet or pantry rather than on a countertop, or, worse still, next to a window or source of heat. In Italy, given the high rate of extra virgin olive oil consumption in this country, bottles do not spend long on shelves in homes or in stores. Buying direct from the producer is a way of avoiding the deleterious effects of poor storage in shops on quality oils.

Extra Virgin Olive Oil contains more than 100 volatile compounds belonging to different chemical families; acids, alcohols, esters, or carbonyls. Concentrations depend on the olive variety, production methods, the storage time of the olives between picking and pressing, and the storage time in the bottle. EVOO can oxidize in three ways; thermo-oxidation, auto-oxidation and photo-oxidation.

Olive oil is particularly sensitive to photo-oxidation because of its content of chlorophyll which is a natural photosensitizer. Chlorophyll is practically absent in other oils such as sunflower or other seed oils.

When oxygen dissolved in Extra Virgin Olive Oil is hit by light it is transformed. Sun energy can be broken down into different types of light; ultraviolet, visible, and near-infrared. The shorter the wavelength, the greater the potential damage. Oxygen in oil will only be energized if it is hit by light with a short enough wavelength – particularly light in the ultraviolet part of the spectrum.

When hit by the light this energized oxygen, known as triplet oxygen, starts a destructive chain reaction, oxidizing fat molecules. Specifically, light triggers chlorophyll which reacts with triplet oxygen to form an excited state of singlet oxygen. Singlet oxygen is a highly reactive molecule. The reaction rate of singlet oxygen with foods is much greater than that of triplet oxygen. Lipids, or fat molecules, are responsible for texture and flavor in food, and when oxidized form aldehydes which have an undesirable taste and smell. The result is a rancid oil with decreased nutritional value.

There is good news for consumers of our oil; studies have shown that the higher phenolic content of olive oils is directly linked to an increased stability of the oil, and consequent slowing of the oxidation process.

Colored glass that absorbs UV light will best protect the oil from oxidation. If UV light can penetrate, the bottle will not give any protection to the oil, regardless of how dark or light it is. Every color of glass has a distinct ‘absorbance’ fingerprint. Some colors absorb light better at different wavelengths than others. Indeed, that is the exact reason why they are perceived by our eyes as having different colors in the first place.

We carefully chose our bottle to offer the most complete protection to our precious oil… please remember to look after it carefully!

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