What is the little capsule inside a Guinness bottle in the United States, CO2?

MotherGoose

Using brain cells that might have solved the third-world debt crisis, a couple engineering types invented a little plastic device, known in brewing circles as a "widget," that's placed in each can (not bottle) of Guinness Draught. (See patent info at www.ivo.se/guinness/patent.html.) When you pop the top and pour, the pressure in the can drops to ambient, stout squirts out of the widget, and nitrogen is liberated from solution and aerates the exiting beverage. Result: nitrogen microbubbles galore, same as if the pouring were done by your local barkeep. http://www.straightdope.com/columns/000526.html Mar 17 04, 12:21 AM