Last year, Left Hand Brewing in Longmont, Colo., made news when they tried to trademark the term “Nitro.” Left Hand Milk Stout had been popular for years, but it really took off when they started serving it with a nitro pour.Beers served from nitro taps are carbonated with nitrogen gas rather than carbon dioxide (or a 70 percent nitrogen mix, to be specific), resulting in smaller bubbles that create a creamier texture.For most people, the first experience with nitro is their first pint of Guinness. It certainly …