The Guinness Brewery says that the perfect pour for their beer is so difficult an operation that you really can’t get a perfect Guinness from anyone other than an authorized pouring expert — and some say it decreases in quality the moment you leave the Brewery itself. However, most beers (and fans) are not so persnickety as Guinness. In most cases, the perfect pour is centered around achieving the perfect amount of foam (or “head”) at the top of the beer.
Hong Luo, physics chair at the University at Buffalo recently explained the science behind a good beer-pour, which turns out to be both simpler and more advanced than you might expect. The basic principle at work is one with which we interact every day: air pressure. The pressure exerted by the Earth’s atmosphere at sea level is stronger than many realize, pressing on humans and everything around us with an ever-present force we’ve evolved to tune out. We can’t feel the power of atmospheric pressure very directly, but we can see its effects.
When the liquid in a beer leaves the bottle or can, it will leave behind an area of low pressure — what air is in the back of the vessel will now be spread out over a larger volume. Once this low-pressure zone reaches a certain strength, there’s no stopping it: Each time liquid “glugs” out of a bottle or can, atmospheric pressure is forcing a bubble of air up into the low pressure zone to equalize them.
This chaotic glugging behavior is responsible for a good portion of the world’s bad pours. One solution is to pour more slowly, maintaining an open area at the top of the opening so air can rush in without disturbing the flow of liquid. A more convenient solution, however, is to include wide mouths on the beer vessel, or a second hold elsewhere on the can — both achieve the same thing, allowing the atmosphere to fill the back of the can.
Heavier beers, like this stout, often require more violent pours to mix up heavier particles.
Combine this advice with a tilted glass, so beer doesn’t pick up too much speed on its way from spout to glass. Let it hit the side of the tilted glass at a relatively low velocity, then slide down to the bottom easy as you please. Don’t forget to bring the glass vertical relatively quickly though — it wouldn’t really be a quality pour without at least a little foam, after all.
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