"You're dealing with the exact same beer and all the specifications of that beer are exactly the same, with the exception of the volume of dissolved carbon dioxide, which is much lower," Hunter says. "By virtue of that and the nitrogen gas that is in there that is rushed out of solution and comes through in the cascading effect, you're getting a beer with less carbonation in it so you're getting a creamier mouth feel and changing the way your palate perceives it texturally." That said, both beer geeks and average drinkers have their doubts. Tucker says his reviewers' most common complaint about nitro beers is that nitrogen diminishes beer's aroma by trapping it under a layer of fine foam. That claim is unfounded, he says, because the nitrogen bubbles in the head are still very active. Tucker notes that nitrogen can be great for adding a creamy texture to chocolate- and coffee-infused beers such as Dieu du Ciel's Aphrodisiac and Peche Mortel, but he and Berkshire Brewing's Hunter acknowledge that nitrogen can make citrusy beers less acidic. For the IPA-averse, that's not such a bad thing. "We've actually experimented and run all our beers through nitro and found that some we thought would be great were horrible and some we thought would be horrible turned out to be gems," Hunter says. "With the IPA, people flocked to it because the nitrogenation process and the dispensing process releases a lot of the aromatics and strips some of the perceived bitterness, so it has a different effect and comes out seeming like a different beer." Even the subtle changes nitrogen produces in a beer have made more brewers consider using it. Hunter and Berkshire brewing are building a tank specifically for nitro beers that will increase the possibility of doing other styles and speed up the nitro process. Longmont, Colo.-based Left Hand Brewing recently released a nitrogen version of its flagship Milk Stout and eliminated the need for clunky nitrogen widgets that rattled around in previous bottled incarnations of nitrogen beers. As is often the case with nitro beers, Left Hand took its cue from Guinness, which eliminated nitrogen widgets from its bottles a few years back but continues to make nitrogen a core part of its packaged goods business. While Guinness doesn't exactly give out the secrets of its nitrogen-adding process to craft competitors, its master brewer seems acutely aware of why other breweries want to have their beers nitro-powered for St. Patrick's Day and whenever else their local bar can spare a nitro tap. "It's the greatest beer innovation of all time," Guinness' Murray says. "It transformed the brand Guinness and made us the lighthouse beer that you have to craft behind the bar." -- Written by Jason Notte in Boston. >To contact the writer of this article, click here: Jason Notte. >To follow the writer on Twitter, go to http://twitter.com/notteham. >To submit a news tip, send an email to: email@example.com.