Brewing Eisbock

February 16, 2017 By K. Florian Klemp

Have you run the table on brewing strong beers? If imperial everything, barley wine and quads no longer excite you, how about taking a stab at eisbock? For the uninitiated, eisbock is bock subjected to freezing, creating a fraction of ice that is then removed, concentrating the beer. Eisbock is a rarity, made by scant few commercial brewers and not often attempted by homebrewers. For those proficient in making German lagerbier, specifically doppelbock, it is a mere procedural step beyond. Eisbock is made to intensify the inherent malty depth and potency of bock, making it a beer without peer.

It is said that eisbock was invented at the Reichelbräu brewery in Kulmbach, Upper Franconia, around 1890 when some kegs of bock were unwittingly left outside on a particularly frigid night. While salvaging the beer, the unfrozen portion was found to be potent and profoundly delicious. This serendipity inspired the brewery to make eisbock a regular offering. The original Kulmbacher Eisbock is still brewed and can be cloned at home.

Base Recipe

Eisbock is elusive, rare, expensive and a bit challenging to make, but can a similar beer be made without freeze concentration? Under perfect circumstances, yes, but the formidable strength, 9% and well beyond, tests the performance limits of most bottom-fermenting yeasts when used within their comfort zone.

Flirtation with the alcohol tolerance limit can result in underattenuated beer, while pushing the temperature limit can produce off-flavors, risks I’m not willing to take. Well-crafted eisbock is malty-sweet but not cloying, properly attenuated, mildly estery and clean as a whistle.

When cobbling doppelbock recipes together, I always recommend considerable reliance on base malts, especially melanoidin-rich Munich, as the optimal strategy. I find excessive amounts of character, coloring or roasted malts and grains (more than 10 percent of the total) unnecessary, as the high-gravity wort, kettle caramelization/Maillard reactions and contribution from toasted malt provide plenty of richness, aroma, flavor depth, body and appropriate coloration. Freeze concentration will enhance those attributes. Your mileage may vary; go with your best doppelbock recipe.

Extract brewers should use Munich malt extract, a convenient 50/50 blend of pilsner and Munich malts, in lieu of base malts.

Mash at 152 to 154 degrees F for medium to full body, and aim for OG 1.074 to 1.085. Use noble hops at 20 to 25 IBUs with low aromatic additions. My favorite strong lagerbier yeast strain is Wyeast 2308, as it produces malty brews and ferments worry-free up to 62 degrees F and 9%, adding a welcomed technical buffer under most circumstances. Any flaws will also be exaggerated in the finished beer.

Robust fermentation and yeast health are critical, so begin with a strong yeast starter and ensure good aeration at pitching. Finish fermentation with a diacetyl rest (65 degrees F for 24 hours), then rack and lager at 32 degrees F for 6 to 8 weeks, or until the wort is brilliantly clear.

Icing

After cold-conditioning comes the step that separates, quite literally, eisbock from other beers. The objective is to freeze 20 to 40 percent of the total volume at temperatures just below freezing. Use a freezer set at 25 to 28 degrees F, a refrigerator cranked to its highest setting, or the au naturel method of setting the container outside if the weather cooperates. Carboys, lidded buckets and corny kegs all suffice.

There is no decisive way to determine when the proper amount of ice has formed, so keep in mind that visual and physical inspection during the freeze process is key. Ice will float on the beer, so swirling and stirring will not only help to assess the volume of ice and degree of freezing, but also help separate the frozen and liquid fractions.

The water in the beer should begin to freeze and get a bit slushy within 24 hours. Keep close watch on it over a couple of days. If it is overfrozen, allow thawing to readjust. Carboys allow easy visual inspection, but could potentially crack. Siphoning is the only option for transfer post-freezing.

Lidded bottling or fermentation buckets are the best option in my opinion. The wide opening allows easy inspection and manipulation. Ice can be stirred easily and scooped out if desired. Beer and ice can be separated by either siphon or bottling spigot.

Corny kegs offer the same advantages as buckets, but the opening is smaller and visual inspection a bit more difficult. Swirl or rock the keg as freezing progresses to break up the ice and estimate the volume of ice without breaching the opening. For a fully closed system, rig up a “trans-corny” jumper tube, from liquid to liquid fitting, and push the beer with light CO₂ pressure, leaving the ice behind.

One could also distribute the beer among several gallon jugs for freezing if the other methods aren’t feasible or only a regular refrigerator freezer is available. Save the residual ice and allow it to thaw to estimate the degree concentration by correcting for volume.

Conditioning and Aging

Carbonation always adds a bit of life and aromatic enhancement, but with strong beers, it is not imperative, and low carbonation is preferred. To bottle, underprime to offset the potential fermentation of residual sugars, and add a dose of fresh yeast since the freezing and high gravity will conspire to cripple the primary yeast. Test for flavor and carbonation after one month. This beer will continue to mature and improve for months if made and archived well.

Kegged eisbock has some advantages, as it permits optimal carbonation control and allows sampling over a long period of time as the beer matures and evolves.

Editor’s Note: This story appears in the March 2017 issue of All About Beer Magazine.