Packaging is as important to good beer as proper brewing and serving methods. Beer is relatively easy to damage. It is actually a fairly delicate product. It might not be the most interesting thing about our favorite beverage, but it is worth knowing about the containers that deliver our beer to us.
Beer of any kind has three main enemies as it travels from the brewery to your glass: light, heat, and oxygen. The perfect container would protect beer from all three. However, there is not much that packaging can do about heat; that is left in the hands of the distributors and retailers. The most we can hope for from our containers is that they prevent exposure to light and oxygen.
Besides protecting beer from light and oxygen, another concern when packaging beer is pressure. In order to produce the right amount of fizziness in the beer, the container needs to be airtight, strong, and well-made enough to resist the internal pressure of carbonation.
Over the years, brewers have come up with four basic types of packaging: casks, kegs, bottles, and cans. Each type of package protects beer in different ways with varying degrees of success. The result is that the same beer served from each these containers can taste quite different.
Although a few brewers still use wooden casks, most modern casks are metal. Traditionally, brewers fill casks with unpasteurized, still beer along with a measured amount of sugar and then seal them. Since there is still yeast in the beer, the sugar kicks off a secondary fermentation that carbonates it.
Casks have been around since before brewers understood yeast. Consequently, they do not completely address the protection needs of beer and require the most amount of care. When casks arrive at their destination, they must be stored on their side in a cool place until that secondary fermentation is completely finished. Determining when that is is up to the pub or restaurant, so casks need to be handled by someone properly trained and experienced with casks.
Once tapped, casks allow the beer to come in contact with oxygen and the clock starts ticking; the beer must be drunk within a matter of days before it spoils. The oxygen introduced produces diacetyl that adds a buttery or butterscotch flavor to the beer. Although diacetyl in a beer at detectable levels is generally considered a mistake, it does not have an entirely unpleasant taste and fans of cask ale embrace it as part of the experience.
The cask ale tradition is strongest in the United Kingdom where it is jealously guarded by the Campaign for Real Ale or CAMRA. The organization identifies unpasteurized, package-conditioned beer as the only real beer, making casks and a few bottles the only acceptable containers. CAMRA is an interesting organization. Criticized as strident and too unyielding in its definition of beer, it nonetheless played a key role in saving the cask ale tradition from near extinction in the 1960s and 70s.
The beer keg is really the modern evolution of the cask. Kegs solve the oxygen problem of casks. And, since kegs are made entirely of metal, there is no chance that kegged beer will become light struck.
Kegs work by using pressurized gas–either carbon dioxide or a carbon dioxide and nitrogen mixture–to force the beer out. As beer is dispensed from the keg, more gas is forced in, maintaining the pressure on the beer and thus keeping is carbonated and protecting the beer from oxygen.