Ever wondered why draft Guinness has that super-rich, creamy foam that seems to cascade downward in the glass? The answer is gas. Nitrogen gas to be exact.

In the 1950s, brewers at Guinness developed the method for carbonating beer with a blend of nitrogen and carbon dioxide. The intent was to mimic the creamy, low-carbonation mouthfeel of traditional cask-conditioned ales at a time when beer service in the UK was transitioning to more modern methods of draft beer dispensing.

Cask-conditioned ales develop their carbonation through refermentation in the vessel from which they are served. Beer is either poured by gravity from a cask on the bar or pumped to the faucet with a device called a “beer engine.” In modern draft systems, beer is pushed from the keg to the faucet with pressurized carbon dioxide. The result is a beer with significantly higher and pricklier carbonation than that of traditional cask service.

Nitrogen is very difficult to dissolve into beer. It requires pressure levels much higher than those typically used to move beer. So when the beer is poured into the glass, those nitrogen bubbles quickly dissipate. The loss of gas results in lower-level carbonation, giving that smooth, creamy mouthfeel. That rapid release of nitrogen creates a rising column of bubbles in the center of the glass that forces the beer and bubbles along the wall to sink, causing the characteristic cascade. Nitrogen makes smaller bubbles than carbon dioxide, resulting in that familiar creamy head.

But nitrogen gas affects more than just mouthfeel and appearance. Carbon dioxide is not neutral. Our taste buds perceive it as lightly sour. Additionally, the higher carbonation affects the expression of malt and hop aromas and flavors. Compared side by side, the same beer carbonated with nitrogen and carbon dioxide can almost seem to be entirely different brews.

In the 1970s, Guinness developed a technology to get that nitrogen effect in a can. Since then others have followed suit. Now there are a number of packaged, nitrogenated beers available on store shelves.

Available bottled in both Nitro and regular form, Left Hand Milk Stout is a great beer to compare the effects of nitrogen carbonation. Flavors of coffee and bitter chocolate are present in both, but Nitro Milk Stout pushes the chocolate far to the front, while the regular version favors coffee. Acrid, roasted malt character is more apparent in the regular version. The nitro comes off sweeter. Nitro Milk Stout gives the impression of a soft, comforting blanket compared with the edgier profile of the other. Each is delicious in its own way.

Left Hand has also released nitro versions of its Hard Wired Coffee Porter and Wake Up Dead Imperial Stout. Both are worth checking out.

Boston Beer Co. has introduced three new canned nitro beers into the Samuel Adams family — Coffee Stout, White Ale and IPA. Nitro Coffee Stout starts with the woody, roasty aromas of freshly ground coffee beans. Underlying chocolate notes bring added complexity. The flavor follows suit with additional touches of caramel and vanilla. Moderate sweetness makes it a bold cup that isn’t bitter.

Not all nitro beers are stouts, as demonstrated by Samuel Adams Nitro White Ale. I was hesitant about this one. The name and the use of orange peel, coriander and grains of paradise led me to expect a Belgian-style witbier. Belgian-style beers without the characteristically high carbonation can be a disaster. But this American-style wheat beer proved to be quite pleasant. Bready, wheat malt is the driver with bright lemon and orange citrus adding high notes. The coriander is prominent, but not overwhelming. Grains of paradise leave a peppery bite in the finish.

Samuel Adams Nitro IPA is good, but perhaps the least successful of the three. Nitrogen can have the effect of lessening the expression of certain beer flavors — particularly hops. The aroma of this one promises huge fruity hops. Tangerine and grapefruit, pineapple and mango explode from the glass. Unfortunately, these aromas don’t carry over to the flavor. Instead you’re left with pithy bitterness and not quite enough malty sweetness to balance it. The creamy texture smoothed it some, but it still left me wanting more of that hop fruitiness.

Guinness Nitro IPA takes us back to the brewery that started it all. This hybrid India pale ale delivers All-American hop aromatics, but a flavor profile more reminiscent of England. The nose bursts with juicy lemon/lime citrus, grapefruit, and pineapple. Low, minty, herbal notes give a hint of what’s to come. The flavor has a stronger malt presence, with the toffee and biscuit that typifies English malts. Bitterness is only moderately high. Hop flavors shift from juicy fruit to earthy and herbal, with low citrus overtones. It goes out dry with lingering bitterness, toffee and herbs.

 

Michael Agnew is a certified cicerone (beer-world version of sommelier) and owner of A Perfect Pint. He conducts private and corporate beer tasting events in the Twin Cities, and can be reached at michael@aperfectpint.net.