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Dear Dr. Vinny,

I know that sunlight can damage red wine, especially while it's fermenting in a carboy. Is the same true for Chardonnay or Pinot Grigio? I see a lot of white wines bottled in clear glass.

—Steve, Sparks, Nev.

Dear Steve,

It sounds like you’re experimenting with some home winemaking. Good for you! In general, it’s important to protect your wine from exposure to ultraviolet light. It’s particularly important when fermenting your wine in a clear glass carboy, because the light can harm the yeasts and interfere with your fermentation. Sunlight can also affect the temperature, and the yeasts can die if it gets too hot.

In addition to degradation and premature aging, sunlight can also cause wine to become “light struck,” a phenomenon more commonly associated with beer. A photochemical reaction forms hydrogen sulphide and mercaptans, which can cause skunky, cooked cabbage or struck-match notes. Whites, sparkling wines and rosés are more susceptible to getting light struck than reds, since red wines have more tannins, and tannins are known to be protective against this process.

Despite that, you're correct that many white wines and rosés are bottled in clear glass. There are two main reasons for that: tradition (which is very prevalent in wine packaging) and marketing (it’s appealing to see the color of the wine you’re thinking of buying, especially for rosé). These wines are made to be consumed when near-term, and best stored in a dark refrigerator or cellar until consumed.

Fortunately, most wine isn’t bottled in clear glass (the industry term for this clear glass is "flint"), and tinted glass filters most of those harmful UV wavelengths.

—Dr. Vinny

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