A cold beer on a hot day is one of life's wonderful small pleasures. Although many bars and beer lovers refrigerate their kegs to extend the life of the beer and keep it pleasantly cool, it's important not to let the temperature get too low. At very low temperatures, the beer in a keg can wholly or partly freeze.
The Science of Suds
Ethyl alcohol, commonly called ethanol, is the type of alcohol found in alcoholic drinks. Because of differences in molecular structure, ethanol has a much lower freezing point than water: Pure ethanol freezes at 173.4 F below zero, while water freezes at 32 degrees F. However, like all alcoholic beverages, beer is a solution of ethanol in water. As a result, its freezing point is between that of ethanol and that of water -- and much closer to water.
When Cold Beers Go Bad
Most beers have a relatively high freezing point because of their low percentage of alcohol by volume. Because the amount of alcohol in beer varies, the exact freezing temperature will vary slightly from beer to beer. However, retailers typically put the freezing temperature of beer at around 28 F. They usually recommend a serving temperature of around 34 to 38 degrees F.
A Frozen Fraction
When beer gets too cold, it will start to freeze -- but it won't all freeze at the same time. The alcohol in beer won't freeze until it gets closer to the freezing point of ethanol. What happens as the temperature drops is that the water in the solution begins to freeze out. Ethanol molecules keep some of the water in its liquid state by preventing them forming a solid, but some of the water will turn to ice, leaving a slush in the keg. This "fractional freezing" can even be used to concentrate beer, producing winter ales with higher alcohol levels.
Why Serve Cold?
With beer freezing at around 28 F and many bars serving beers at 34 to 38 F, it's easy to see how small variations in refrigerator temperatures can lead to a frozen keg. If this is the case, why do bars refrigerate beer at all? The first reason is to inhibit bacterial growth, preventing beer from spoiling. Additionally, some drinkers prefer the taste of cold beer. However, traditional beer advocacy group the Campaign For Real Ale (CAMRA) condemns overly cold beer, claiming that serving at low temperatures masks the beer's subtle flavors. It recommends serving beer at cellar temperature, around 52 to 55 F.
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