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Can light change the smell of a liquid?


Packing certain liquids in transparent containers is not a good idea, especially white wine. Wine lovers may have noticed a disturbing recent trend. Whites, which until now were normally sold, like their red cousins, in green bottles, are now beginning to appear in transparent. It is believed that this increases sales by showing the liquid they contain. But, although it can attract sight, such packaging can end up ruining the olfactory experience after uncorking, since light is a powerful driver of chemical change. This was demonstrated by a study by scientists from the Edmund Mach Foundation, in northern Italy, published in Proceedings of the National Academy of Sciences. Here we tell you about its main results. Lightstrike, known to the French as goût de lumière, occurs when incoming photons trigger undesirable photochemical reactions that leave the wine with a smell of "boiled sprout" or "wet dog." Some are more susceptible than others, reds are usually protected by their tannins and pigment molecules known as anthocyanins; whites, less. In the study carried out, the effects on odor change were observed for 20 varieties of white wine depending on the packaging and exposure to light. To do this, they left bottles packaged in transparent glass and left in the light (similar to the supermarket), green bottles in an equally illuminated place and bottles in transparent glass but stored inside cardboard boxes. After 60 days, the researchers evaluated the "odor footprint" of each bottle, using gas chromatography to extract and separate volatile compounds..

How did the olfactory footprint change

As expected, the olfactory footprints were grouped according to the type of grape and the bottle. They identified which odorous compounds were most sensitive to light and, therefore, were most likely to play a role in the light strike. Beta-damascenone, which gives notes of roasted apple, quince or flowers, was the compound most affected by light. In a transparent bottle, the concentrations of this molecule decreased by 65% after a week. In a green one, even after 50 days, it had decreased by only 40%.

Another victim was geraniol, which contributes to the aromas of roses, fruity or citrus fruits of some wines. In transparent bottles, its concentration fell 30-45% after 21 days. In comparison, it only decreased by 25% after 50 days in green bottles, and there was no decrease in the bottles in the boxes. In addition to losing these desirable and characteristic aromas of a good wine, new undesirable odorous compounds emerged. For example, the amount of 4-hepten-1-ol, reminiscent of fish and stale oil, tripled in transparent bottles and increased only by 10-20% in green bottles. The conclusion is that it is a terrible idea to pack whites in transparent bottles and leave them exposed to light. As usual, traditions are there for a reason.


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