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Yes, it's a physics related question. Read on.

I know from general knowledge that in order to produce a decent wine, you must keep it in a dark place. Therefore, from my knowledge of physics I guess that the process of wine making doesn't need much energy (I mean the reactions etc). Also I presume it gets the energy from visible light, IR, UV light and all the electromagnetic spectrum. However, you can see most of the wine bottles are painted in dark colors, which brings me to think that they attract more energy from electromagnetic waves than they would if they were painted in brighter colors. However, in those cellars they're kept in, hardly any light goes inside, but still wouldn't it be more efficient to paint them in solid (so you can't see through) colors (white spray, duh)?

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2 Answers 2

[not really a physics question... maybe more like Chemistry?]

As far as I know, wine bottles are not "painted" at all. It's the glass of the bottle itself that is tinted with a dark color. It would probably take more effort (and more cost) to actually paint the outside of the bottle. It's simply easier to tell people to keep the wine out of sunlight. (And of course wine connoisseurs will always prefer tinted glass bottles for aesthetic value)

Straight out of Wikipedia:

The main reason for using coloured or tinted glass is that natural sunlight can break down desirable antioxidants such as vitamin c and tannins in a wine over time, which impacts storability and can cause a wine to prematurely oxidise. Dark glass can prevent oxidation and increase storage life. It is therefore mostly ready-to-drink white wines with a short anticipated storage lifespan which are bottled in clear colourless bottles.

Another important reason that wine is kept in a cellar is to maintain a more constant (and cooler) temperature.

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1) The energy for the fermentation process comes from the sugars in the grapes. Yeast and other microflora aerobically extract energy from the sugars producing alcohol as a waste product of the process.

2) I doubt that the dark glass plays much of a practical role. More likely, it is simply tradition dating back from when clear glass was very expensive. Real glass is opaque to UV radiation and it is UV that does 99% of chemical degradation. Likewise, the practice of storing wine in a cool, dark place probably just comes from the pre-climate control era when dark cellars or caves were the only stable thermal environments.

3) Today, white wines are routinely put in clear glass bottles and you will sometimes see red wines in clear bottles as well. However, since everyone associates dark bottles with red wine, it's a marketing risk to do so. Cultural inertia is hard to overcome.

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