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Why do wines tend to be stored in dark bottles?

In the world of wine there is an established practice that consists in keeping wine in dark bottles. You must probably have noticed that wines come in dark green or amber bottles. Have you ever wondered why? Where does this tradition come from?

Actually, there is more than one reason. Apparently, in the past, making clear glass was almost impossible, since natural impurities were difficult to remove and resulted in an opaque amber tint to the glass. It was almost by chance that glass-makers produced green bottles for the first time: The smoke rising from coal-fed furnaces used in the glass-making industry turned the glass green as a result of the iron oxide impurities it contained.

With time, winemakers realised that storing the wine in dark bottles prevented it from degradation. Wine can be affected by sunlight. Both UV light and visible light cause a series of chemical reactions whose products no-one wants on wine tasting notes. Scientists have shown that dark green glass blocks between 30 and 60% of harmful rays, while amber glass blocks about 90%.

Nowadays, glass makers can produce bottles of any colour. However, tradition plays a major role in the industry, and there are cost-saving reasons too. Amber and green bottles are cheaper to make. Other colours require removing iron oxide impurities and this can be very expensive.

Although the most important reason to keep wine in dark bottles is to avoid damage from light, wineries have aesthetic and economic motives as well to choose dark bottles for the wines they make.

To sum up, wine is a precious product that continues to evolve inside the bottle, so choosing tinted glass to store it will better protect it from oxidation as it ages.

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