It’s a matter of quality — dark glass shields the single olive oil from the damaging effects of light. This is also why many health goods are packaged in brown bottles, wine is packaged in deep green glass, and clear glass milk bottles have given way to opaque cartons.
Even a few weeks of exposure to light will hasten the aging of organic extra-virgin olive oil. To slow this operation, keep your oil in a dark, cold cupboard rather than on a countertop, which is prone to be warmer and brighter.
Is it True that all Black Glass Bottles Used to Store Extra Virgin Olive Oil are the Same?
The oxidation of extra virgin olive oil occurs in two stages. The first is known as auto-oxidation, while the second, and possibly the most harmful, is known as photo-oxidation. As the name implies, photo-oxidation is triggered by light.
The good old-fashioned oxygen found in air and dissolved in Extra Virgin Olive Oils isn’t very harmful on its own. Nevertheless, if it is struck by light that packs a powerful enough energetic punch, it can drive the normally innocuous oxygen into a new and hazardous psychotic condition. This energized oxygen, known as triplet oxygen, initiates a damaging chain reaction that oxidizes fat molecules left, right, and center. The result is a rotten oil that lacks fresh olive flavors and, worse, infuses your dish with the awful flavors of an old fish and chip restaurant or suburban corner grill.
Avoiding photo-oxidation is as simple as not exposing the extra-virgin olive oil to light. To that aim, excellent Extra Virgin Olive Oil manufacturers package their oils in dark glass bottles or cans and advise their consumers to keep their oils in a dark environment. While tin cans are entirely lightproof, dark glass is not. Extra Virgin Olive Oils are stored in a variety of colored glass with varying degrees of blackness. Examine closely: some are a traditional green, while others are more of a “sea green” hue. Others are more olive in hue, while yet others are amber.
Many extra-virgin olive oil manufacturers believe that the darker the glass, the finer, and that’s it. They would, however, be incorrect.
Only light with a small enough wavelength – notably light in the ultraviolet region of the spectrum – can activate oxygen. As a result, colored glass that traps UV radiation is the greatest way to preserve the oil from oxidation. Those that allow UV light to pass through will not protect the single olive oil, irrespective of how black or bright the bottle seems to the eye.
So, how can we assess the efficacy of various glasses and materials of virgin olive oil in blocking UV light? For this task, scientists employ a device known as a spectrophotometer or Spectro. It sends a beam of light with constantly changing wavelengths through the glass and measures how much of that light does not pass through.
Each hue bottle has a unique ‘absorbance’ fingerprint. Certain hues absorb light better than others at various wavelengths. That is, after all, why our eyes interpret them as having various colors in the first place.
When it comes to UV protection, the olive/brown variant outperforms the green version. However, neither is flawless. So, regardless of whether the virgin olive oil is in dark glass, keep them in a dark environment. The PET is a pleasant surprise. It absorbed quite effectively in UV-B but had a very clear window in UV-A. UV blockers are integrated into certain PET. This was unmistakably one of them. Not that you’d be able to know by looking at it!
The stability of the organic extra-virgin olive oil is also why there are so many various forms of olive oil packaging. Non-transparent metal canisters shield the olive oil from light and air. It is also effectively protected by dark-colored, particularly green, glass bottles. Transparent plastic bottles, on the other hand, offer less security. This is less of an issue if the oil has been refined, but for unrefined oils, it might hasten the loss of quality.