Why does beer continuously bubble

Those are more or less out of your control, but there are some things you can do to ensure you enjoy the full frothy glory of your suds. So what can you do to get the softest, creamiest beer possible?

This ensures nothing will neutralize your foam or create unwanted nucleation points that lead to loss of head. To achieve the industry standard beer clean glass, follow these steps:. Wash the glass in warm, sudsy water. Rinse it in clean water. Let the glass air-dry upside down on a rack. Temperature is also important, as it may affect bubble size and uniformity, which feed back into the overall mouthfeel.

Temperature will vary based on beer style, but as a broad rule, ice cold and room temperature will offer you the ideal experience from a beer foam standpoint. Start gentle, with the classic degree angle, and pour down the side. As you reach the final quarter of the pour, pour hard, straight down the middle, to encourage nucleation. The ratio of soft pour to hard pour will again vary with beer style. Hefeweizens and wits generally benefit from a more vigorous pour, while stouts should be poured more conservatively — often meaning filling the glass halfway so you can top the head off continuously.

And of course, with nitros, you go hard from the start. To generate that much of an increase, he realized, the pressure at the bottom of the glass would have to be eight times the pressure at the top. Some back-of-the-envelope calculations showed that a glass of beer would have to be feet tall to generate that much pressure. Another problem with the pressure theory: It couldn't explain why bubbles in beer should act any differently from bubbles in water.

It turned out that pressure differences make only a minor contribution to bubble expansion. Instead, like snowballs rolling down a hill, bubbles expand because they accumulate material as they go. The process starts when you open a bottle of beer. The sudden drop in pressure encourages dissolved carbon dioxide to escape from the beer. Most escapes in bubbles that form at the sides and bottom of a glass, where microscopic cracks serve as starting points, or nucleation sites, for carbon dioxide to gather.

When the carbon dioxide at a nucleation site reaches critical volume, a bubble detaches from the glass and launches itself toward the beer's head. The reason that bubbles expand and accelerate as they rise is that bubbles themselves act as nucleation sites. Each attracts more escaping carbon dioxide -- or, as Zare puts it, "bubbles nucleate bubbles. Nucleation also is responsible for the fizz that results from adding ice, sugar or salt -- all crystalline in microstructure -- to a carbonated beverage.

That's not all: We place priming sugar in the bottles. That's just how many bubbles a batch of homebrew produces. Bubbles form around nucleation sites, which are impurities in the beer rare or on the surface of the glass common that allow for CO 2 to come out of solution.

Beer "fobs" or foams excessively when there are too many nucleation sites, but simply rinsing the interior of the glass fixes this by washing impurities away or filling in scratches with water. Careful observation of a freshly poured pint of beer reveals that "beer bubble size varies slowly with nucleation site size and is pretty much constant for a given site," Denny, p.

There are actually two types of foam: "wet foam" consists of spherical bubbles with liquid beer between them and "dry foam" consists of polyhedal bubbles with no liquid between them. Liquid foam slips and slides while dry foam is stiff and sticky. Now we can come up with three equations that describe the change in beer foam composition over time:. Disproportionation is when large bubbles get larger and small bubbles get smaller as the small bubbles pass their gas to the large bubbles.

It is unique to dry foam, where the polyhedral bubbles share boundaries, and happens contrary to what people would likely expect due to the connection between size, surface tension, and pressure. In short, smaller bubbles have higher surface tension and higher pressure.

The pressure, not the volume, equalizes between bubbles, so the small bubbles shrink as they lose gas and the large bubbles grow as they gain gas. Beers on a nitrogen tap or with nitrogen in the cans produce more uniform without disproportionation foam because nitrogen gas is much less soluble than carbon dioxide. This is also why the head on nitrogen beers lasts longer.