Definition - What does Nitrogen mean?
Nitrogen is a non reactive, odorless and colorless gas . In winemaking, it is necessary for yeast as it contains the essential nutrients they feed on. It is beneficial as a preservative in winemaking as it is a stable molecule with a triple bond between two nitrogen atoms. This make-up makes it impossible for nitrogen to react with other molecules in the air.
WineFrog explains Nitrogen
Nitrogen is an essential gas for yeast during the fermentation of wine, however, the most common use for nitrogen is as a wine preservative. While wine is resting and aging in a tank prior to bottling or during some fining stages, nitrogen is gassed into the holding vessel. It is heavier than air, and thus, floats on the surface of the wine, preserving it from any oxygen which can damage the wine.