There are two kinds of people in this world: those who like Guinness and those who don’t. The latter should just skip this post.
One reason for the love/hate split is called something like “Guinness Flavor Product” by the sages of St. James’ Gate. It’s pretty simple: they let 5 percent of every batch go completely nasty-sour, then add it back in.
In reality it’s a bit more complicated than that, but a very small proportion of soured Guinness is what imparts the beer’s famously dry, tart aspect.
Another thing Guinness brewers do (other Irish stout makers too, most likely, though I’m not 100 percent sure) is use flaked oats—otherwise known as oatmeal.
The oats contribute glycerides, the gelatinous compounds that make Guinness feel so thick. You can’t really taste them, but they impart that silky mouthfeel and “weight” that make you think it’s a heavy beer, when it’s got roughly the same density and alcohol content as regular Bud.
And then there’s the nitrogenated “carbonation.” Instead of using straight carbon dioxide, the brewers at Guinness dissolve a mix of nitrogen and CO2 into the beer that roughly approximates their concentrations in the atmosphere (roughly 75 percent to 25 percent, respectively).
So instead of the bubbles looking to equalize with the atmosphere (by losing 25 percent of their CO2, gaining the equivalent in nitrogen and collapsing in the process), the mixed gases stay inside the bubbles—and the head stays on the beer.
As an added bonus, nitrogen also makes smaller bubbles than CO2, so the head is denser. And the nitrogen surging through the beer also smoothens its flavor by stripping away any volatile organics (like hop oils and fruity esters), leaving behind the malty goodness and roasty chocolate flavors we know and love.
Next up, a blind comparison of four other Irish stouts and “the black stuff.”