When you pour the beer slowly down the side of a tilted glass, a smaller head is formed, and more CO2 remains dissolved in the beer. If you hold the glass upright and pour straight into the glass, more gas is released, and a larger head will form. Real a cionados will insist that different beers have different ideal pours. Generally, pour an ale so that it has about half an inch of head, lagers with a larger one, and allow a wheat beer to have a big, pillowy head.
What causes beer bubbles?
Beer bubbles/fizz/carbonation is caused by the action of yeast. When the yeast eat the sugars in beer, they produce a by-product of carbon dioxide (CO2) and alcohol. Carbon dioxide is a gas that dissolves in the liquid and remains that way under pressure until you open the beer. You can further release the CO2 by pouring beer into a glass. When you do this, the CO2 that is released during the pour carries some of the aroma with it.
Originally published in our Micro Brew News' Trivia Time, Free State Brewing Company edition.