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This month's question: What is Eisbock? How would I make one?

Answer: Eisbock is one of those beers that you usually don't find very often. When you do, it is usually a very memorable event. Or perhaps because of the high alcohol content, one that you've forgotten entirely!

As I mentioned last month, eisbock is the strongest member of the Bock family. It is traditionally made by the Kulmbacher brewery in Germany, and by Niagara Brewery in the United States. Schneider also has an eisbock, though this is made from a weizenbock base, as opposed to doppelbock, which is the base for the usual eisbock method.

Eisbock, which is German for "icebock", is made by a process that is unique in the brewing industry: it is made by freezing out water from beer. The resulting brew has a considerably higher alcohol content. The BJCP style guide lists the alcohol level in the range of 9 to 14%. In the United States, this is considered a distillation process. Hence, it can be performed only by breweries that have gone to the extra effort of getting a distillers license.

In addition to boosting the alcohol content, the freezing process results in some flavor changes. As the beer concentrates, the bitterness, final gravity and color are all boosted. Alcoholic warmth is readily apparent. However, the alcohol flavor lacks the fiery nature associated with very strong beers. The reason for this is that the beer is fermented from wort that isn't as high a gravity as the alcohol content would indicate. Typically, eisbock is fermented from a wort that is no stronger than doppelbock, and can even be a bit less. As a result, the final flavor is full-bodied malty beer that is surprisingly smooth.

To make an eisbock, you need to start with a fully-fermented strong bock, or doppelbock. Make sure the beer has had plenty of time to lager, since it won't be able to after doing the process. Note, though, that it doesn't have to be carbonated. If you don't happen to have a doppelbock, fear not. You can buy some commercial doppelbock and give it a try. Then, get a large open-top container you can put in the freezer. Fill it with your doppelbock, and cover over the top with plastic wrap. For best results, note the volume that you are using. You'll need to allow a couple of hours in the freezer for a small batch, or overnight for a larger batch. As the beer chills, you'll see ice crystals forming, and the beer will congeal into a slurpy-like consistency. Once the beer is frozen, you need to get ready to remove the ice. Take a strainer and set it up over a second open-top container. Then dump the slushy beer through. The ice crystals will be held in the strainer while the concentrated beer goes through.

Once the fluid has stopped dripping, note the volume. The ratio of initial to final volume will determine your concentration ratio. If you freeze out more beer than you had planned, just let the strainer sit and some of the ice will melt. If you didn't freeze enough, it might be because your freezer isn't cold enough.

Finally, you need to package and carbonate your beer. The alcohol level is now too high for just about any yeast to work, so bottle-conditioning is not an option. The easiest method is to fill 2 liter soda bottles with the beer and force carbonate it with a carbonator widget. If you've made up enough for a corney keg, carbonate as usual. Traditionally, eisbock is not a highly carbonated style, so don't overdo it. Since the lagering process is already done, the beer should be ready for serving as soon as it has had a chance to settle.

Vital Statistics for Bocks

Style Starting
Gravity
Final
Gravity
Bitterness, IBU Color, SRM Hop Aroma
Maibock (Helles) 1.064-1.072 1.011-1.018 23-35+ 6-11 Low
Traditional Bock 1.064-1.072 1.013-1.019 20-27 14-22 None
Doppelbock 1.072-1.096+ 1.016-1.024+ 16-26+ 6-25 None
Eisbock 1.078-1.120+ 1.020-1.035+ 25-35 18-30+ None