How it works: Another naturally carbonated style, wheat gives weissbiers and hefeweizens a golden color, a cloudy look, and a delicate, sometimes fruity scent. Most wheat beers are bottle conditioned, which means fresh yeast is added just before the bottle is sealed. The yeast cells settle on the bottom after they've tired themselves out re-fermenting the ale, and, in the process, adding an extra blast of carbonation. And, as Jason Alstrom, co-founder of beeradvocate.com, explained, wheat malt is naturally great for head retention. That's the chemistry; now for the physics. When the bottle is poured, the spent yeast cells come out in the last drops. As they fall to the bottom of the glass, they stir the beer's flavors and give the carbonation process yet another kick, so the frothy head is constantly cultivated.
The verdict: The spectacle at the Bukowski Tavern in Cambridge began when the bartender turned the bottle straight upside-down with the neck inside the glass. Since the bottom is thinner, there's less room for air to interfere and less foam bubbled up. In a ceremonial closing flourish, the bartender raised the bottle high over the glass for the last drops to cascade out. Then the yeast went to work, making its commute downwards. A creamy head stayed at a constant half-inch as time passed, sustaining a delicate aromatic hoppiness.