Guinness connoisseurs are already familiar with the widget that creates the proper foam when a can of the stuff is opened and poured into a glass. Now Guinness has created a rocket-shaped device that releases gaseous nitrogen in a bottle, and you don’t need to pour it out into a glass for the correct effect. Purists, of course, will always insist on Guinness from the tap. And super-purists deride any that isn’t from the source in Ireland.