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Slideshow: The Physics Of Oxygen-Free Beer

When it comes to fresh, draft beer, “Oxygen is the enemy.”

So says Jed Jenny, beer manager for The Wine Source in Hampden.

Growlers are usually filled from a tap like a draft beer, and oxygen sneaks in. But one local liquor store, The Wine Source, has installed a custom-built machine called a counter-pressure filler to keep the oxygen out.

Here's how it works: six kegs of beer are kept in a walk-in cooler. The beer lines run through an insulated wall into the counter-pressure filler. The empty growler is placed on the filling arm. The growler is first filled with carbon dioxide, which pushes out the oxygen. Once the carbon dioxide pressure in the growler is about the same as the pressure in the keg, Jenny will reduce the pressure in the growler. This draws the beer out of the keg and into the growler. The filler has a switch which allows Jenny to bleed out any oxygen which may have sneaked back in.

Jenny says little oxygen means beer will stay fresher longer. Added bonus: little foam.