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Dear Dr. Vinny,

Is it true that nitrogen is sometimes used to flush an empty wine bottle before it's filled? Why?

—Kate, South Africa

Dear Kate,

The bottling process isn’t one of the most glamorous parts of winemaking, but it’s still very important (and fascinating). Remember that when it comes to winemaking, many winemakers are on a mission to eliminate or at least regulate a wine’s exposure to oxygen. Too much oxygen exposure and fresh fruit flavors and aromas can disappear and turn to nutty, tired notes; too little oxygen can result in skunky reduced notes.

Bottling is one of those critical moments when wine is at risk of being exposed to excess oxygen. Aside from getting the wine into the bottle, the primary objective of the bottling line is to protect the wine from oxidation.

Some wineries use nitrogen gas to prime the bottles before they're filled with wine. This process reduces the oxygen content by displacing the air inside the bottle and "diluting" it with extra nitrogen. Remember from science class that the air we breathe is already mostly nitrogen—about 78 percent nitrogen, 21 percent oxygen and almost 1 percent argon (an inert gas that's also popular for preserving wine)—and nitrogen in its natural atmospheric form is non-reactive. It plays the straight man to its highly reactive partner, oxygen.

Some bottling lines actually use very, very tiny drops of liquid nitrogen rather than blasting the bottle with gas. Something like a tenth of a gram of liquid nitrogen at a temperature of –320° F will then rapidly expand into gas inside the bottle. A final shot of nitrogen or argon might be applied right before the cork is inserted for added protection.

—Dr. Vinny

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