Eisbock uses a fractional freezing process to concentrate the beer’s strength, and it does so without requiring your yeast to work overtime. The result is a smooth, rich, and intense lager—perfectly suited to sipping on a cold winter night.
Style: The classic type of eisbock is an intensified doppelbock, with amplified bready richness and warm (but smooth) alcohol. It tends to have more noticeable fruit flavors than a typical doppelbock; subtle roast may emerge, too. The key is that less obvious flavors may come to the fore in a finished eisbock. That means that simply making our standard doppelbock, freezing it, and calling it an eisbock is not the most successful approach. The recipe should account for the freeze-concentration, to avoid a beer that is overly sweet, bitter, or alcoholic—because a good eisbock is none of those.
Ingredients: Time for restraint. Don’t try to make the beer intense; let the freezer do the work. Normally for a doppelbock, I use mainly Munich malt with a couple of small add-ons to round out specific flavors. With eisbock, we don’t even need those. This grist is simple: 100 percent Munich (9L), shooting for a starting gravity around 1.080. Don’t worry if you miss by a couple of points—it won’t matter much in the end. Two or three additions of classic German hops for about 20 IBUs should be enough to balance the sweetness and add some earthy, floral flavors. I use Bavarian lager yeast here (Wyeast 2206) for solid attenuation; we don’t want a beer that’s too heavy, even after concentration.
Process: Pitch plenty of yeast and aerate thoroughly to minimize off-flavors and ensure a thorough fermentation. You also want a thorough diacetyl rest, which also helps ensure a more complete fermentation. The fun part comes after primary fermentation. Transfer to a keg for the freeze; you can also use a plastic fermentor or bottling bucket. NO glass carboys—the main thing is to rack into something that won’t crack when the beer starts to freeze. Then put the vessel in a freezer of sufficient size—or outside if it happens to be that cold—and leave it alone. Give it a little shake every few hours, but don’t be surprised if it takes a while to develop that “slushy” sound. After about 10 hours, you should finally get some noticeable freezing. Your goal is to freeze enough water to reduce the volume by about 25 percent. There’s no definitive answer on how long that takes; for me, it’s about 16 hours. Keep checking, keep shaking, and trust your gut.
When you think you have about 25 percent ice, rack the beer out from underneath the ice and package it. You can let the ice melt to find out how close you got to the 25 percent mark (that’s 1.25 gallons/4.75 liters for a 5-gallon/19-liter batch). Whether kegging or bottle-conditioning, carbonate to about 2.25 volumes, and let it age a while to mellow out. Most will be a little rough at first; they can benefit dramatically from lagering for up to three or four months.