Wine on tap is sweeping into restaurants and bars around the Bay Area. It's greener than bottles, and cheaper. And the wine always tastes fresh. Most restaurants pour their wine-by-the-glass selections out of bottles that sit for days, often long after the contents inside have staled. But restaurants with tap systems use an inert gas like argon or nitrogen to push the wine through the lines. That gas also protects the wine for weeks against oxidation.