Beer coming from the tap contains carbon dioxide, a by-product of fermentation. (The other by-product being alcohol.) We go one step further in the serving tank (or keg) by adding nitrogen, Some of this nitrogen vapor dissolves in the beer which also contains the dissolved carbon dioxide.

The presence of dissolved nitrogen allows smaller bubbles to be formed with consequent greater creaminess of the subsequent head. This is because the smaller bubbles need a higher internal pressure to balance the greater surface tension, which is inversely proportional to the radius of the bubbles. Achieving this higher pressure would not be possible with just dissolved carbon dioxide, as the greater solubility of this gas compared to nitrogen would create an unacceptably large head.

a pint of nitro stout with whole grain bread and butter

When the tap is opened, the pressure quickly drops, causing the pressurised gas and beer to jet out. This agitation on the surrounding beer causes a chain reaction of bubble formation throughout the beer. The result, when the beer is poured, is a surging mixture in the glass of very small gas bubbles and liquid.

The surging mixture gradually settles to produce a very creamy head.

That's the story of nitro--it's not just for Guinness any more.

Barley's Draggin' Ass Stout

Style Guidelines: Dry Irish-style Stout. It's light-ish body makes it highly drinkable. We give it a lower carbonation rate and serve on our nitro system for that creamy, masking effect. It's a great pick-me-up for when you're, well, draggin' ass. 

Rotation Schedule:Maybe in the summer--maybe not

Food Pairings: Shepherd's Pie, Irish Stew, Scotch Eggs

Body: medium-light

Color: Jet black

Grain: British pale, roasted and black patent; and American chocolate

Bittering Hops: Argentinian Cascade

Finishing Hops:Argentinian Cascade

Original Gravity: 1.040

IBUs (estimate): 30

Alcohol By Volume: 4.2%

First Tapped: June 13, 2008

Barley's Smokehouse & Brewpub Ale House No. 2xx 1130 Dublin Road Columbus OH 43215