A brewer may take up to several months to brew, finish, and package a keg of beer. The quality and flavor of that beer can be ruined in the few seconds it takes for a beer to travel from a keg to the faucet in a draft system that has not been properly maintained.
The enemies of draft beer may include the following:
Yeast
May result from an extremely small amount left from the brewing process, or it may be wild yeast which floats in the air. It is usually found as a surface growth on components of a beer system that is exposed to the air such as faucets, keg couplers, and drains and can be recognized by its white or grey color.
Mold
Mold is usually introduced into a beer system through exposure to the air. It also is usually found as surface growth on components of a beer system that are exposed to air such as the faucets, keg couplers, and drains and is usually brown or black in color.
Beer stone
The raw materials, grains and water, that are used in the brewing process contain calcium. Oxalic acids or salts are present in hops and may be created during the process of changing barley into malt. The combination of these ingredients and the fact that beer is dispensed at cold temperatures may result in Calcium Oxalate deposits known as beer stone. Beer stone will build up and eventually flake off on the inside of the beer tubing if the system is not properly maintained. High amounts of beer stone may also have a negative effect on taste. These flakes are often grey or brown in color.
Bacteria
Bacteria found in beer are not significantly hazard to human health; however, its effect is noticeable in the appearance, aroma, and taste of beer. The presence of bacteria results in an “off taste” and cloudy appearance that makes beer unappetizing. A beer that tastes sour, vinegar-like, or smells like rotten eggs may indicate a beer system is contaminated with beer spoiling bacteria.
Failing to clean and maintain a beer system on a regular basis will result in the ability to pour a “brewery fresh” beer.
Source: Micro-Matic, USA.