They contain a plastic ball that floats when beer is running through the line. When the beer runs out, the ball drops, blocking the line so air won't pass through it.

In the past few decades, Guinness revolutionized both draft beer systems and how stouts are canned. The key? Nitrogen, and a modified ping pong ball.

Jeromy Krom, owner of Clear Line Draft, cleans the draft lines at Bar Rosa, on Wednesday, Feb. 19. The system here is a short-draw, meaning the beer travels a brief distance from keg to faucet.

Carefully remove the old beer line from the faucet shank. • Remove the old beer line from the keg hardware (either sanke-style, homebrew ball lock, or pin lock) and discard it.

I consulted two experts—a food-safety professional and a restaurant bar manager—to learn about the tap-beer system and how to tell if your beer is actually clean.

It was Saturday, and I was drinking beer at a nameless bar in New York's East Village. Enter two 30-year-old frat bros (brotherhood lasts for life, dude), who took a seat at the bar next to me ...

Wisconsin's beer consumption begs the question, how clean is the beer coming from draft lines at bars and restaurants? FOX6 News learned in many cases, you may never know.