Eis, Eis, Baby
Eisbock is a rare and misunderstood style that is more about process than anything else. It’s related to (and derived from) the doppelbock style, and is created by freezing the beer slightly to concentrate the alcohol and flavors when the frozen water is removed. The science bit here is that alcohol has a lower freezing point than water, so when beer is chilled to slightly below the normal freezing point for water (32 °F/0 °C at sea level), the water portion of beer will begin to freeze first — a process known as freeze distillation or freeze concentration. The slushy, partially frozen water is removed, and the remaining beer has concentrated alcohol and flavor.
An eisbock is not necessarily the biggest or strongest lager, just one that has undergone this freeze distillation process. Traditionally a regional German product, it has been applied to the doppelbock style, so an eisbock is thought of as a lager style. There is no reason why freeze distillation cannot be applied to other base styles, but eisbock is an actual German style not an experimental beer.
This past winter I brewed a doppelbock recipe as a collaboration brew with a local brewpub, and I had to make it as a single-infusion mashed beer, not my traditional double-decocted version. The resulting beer was slightly leaner in mouthfeel, but that is actually an advantage when using it as the base of an eisbock — the technique increases body in the final beer. I think the eisbock method works better when you start with a leaner beer than a huge malt bomb of a lager. It is certainly possible to overdo the flavors.
The style winds up being hard to find in the U.S. commercially because of laws related to concentrating alcohol — it’s basically a form of distillation and technically (read: legally) requires a different (read: more expensive) license. Imported beer may not have the same requirements, and homebrewers certainly have more flexibility in production, which is why I tend to see more of it at homebrew competitions than anywhere else. The Beer Judge Certification Program (BJCP) Style Guidelines categorizes eisbock as Style 9B in the Strong European Beer category, along with doppelbock and Baltic porter.
History
There is a fair amount of lore surrounding the eisbock style. As I say, any explanation that starts with, “as the story goes . . .” usually means “watch out, I’m about to make all this up.” The legend usually involves a hapless brewery apprentice carelessly leaving casks of doppelbock outside during cold weather instead of moving them to the cellar. After discovering that the casks had frozen over night, the brewmaster made the apprentice drink the mistake, which of course led to the apprentice having a grand old time. Of course, no names or breweries are involved, so it’s impossible to verify. I’m not buying it, but this supposedly happened around 1890.
By whatever (accidental or inspirational) means it was created, it is known that brewers at Kulmbacher Brewery were making this around the start of the 20th century. Founded in 1895 under the name Reichelbräu, it is located in Kulmbach in the Franconian region of northern Bavaria in Germany. Casks of doppelbock were placed outside on cold nights, and the liquid was collected the following morning. The process is now done with mechanical refrigeration, of course, but the beer retains the description “G’frornes” meaning “frozen.”
This 9.2% beer is the origin of the style, but not many breweries make such a specialized product. Niagara Brewing Company in Canada used to make a nice example, although it was only 8% ABV. Some smaller American craft breweries might make it occasionally as a special project, although because it is considered a form of distillation it is usually not well advertised (or possibly not made by traditional means).
As a side note, Schneider makes an eisbock version of their Aventinus weizen-doppelbock that weighs in at 12%. Since this is based on a weizenbock not a doppelbock, I consider this to be a specialty beer in the categorization scheme. This is a modern product dating to 2002, while the original weizenbock was first made in 1907. Although not part of the style for competition purposes, comparing the two versions side-by-side is an interesting experiment (as long as you aren’t driving any time soon).
Sensory Profile
The easiest way of thinking of the style is as a richer, stronger dark bock or doppelbock, but that’s not a complete picture. The freeze concentration process also concentrates flavors (and flaws), producing a darker color and more full-bodied mouthfeel. It isn’t just simply a stronger doppelbock since the process is integral to the style. Some doppelbocks (or other strong lagers) may be stronger than eisbocks. Remember, some commercial examples are under 10% ABV. So, please don’t think of eisbock solely in terms of alcohol.
An eisbock is deep copper to dark brown in color, which is darker than the dark version of most doppelbocks. Yet this color is not derived from roasted malts, so don’t expect any burnt or roast flavors, except perhaps a faint chocolate note. The super malty-rich flavors of Munich-type malts (including dark Munich malts) is prevalent, with their strong Maillard product flavors imparting richness and depth.
An eisbock is a strong lager, so it should have the smooth palate of other German lagers, even if the body is quite full. The alcohol warmth should be noticeable, but hot and harsh edges are still a fault. Concentrated alcohol-related flaws, such as fusels, are a serious fault. The alcohol finish can also help balance the malty richness on the palate. The finish should not be sugary-sweet, sticky, heavy, or cloying, either.
The aroma is like a dark doppelbock, but more concentrated. Rich bready, toasty malt with light caramel or chocolate notes is common, and a dark fruit character (plums, grapes) is also frequently found in support of the malt. Hops are not found in the aroma or flavor, and just enough bitterness is present to avoid a cloying character. However, the alcohol also can provide some of the counterpoint to the malt richness, not just hop bitterness.
Compared to a doppelbock, an eisbock can have lower carbonation and less of a head. But some examples may have higher carbonation to attempt to offset the increase in body. It should still be a clear beer, although it may be too dark to tell in normal light conditions. The body is fuller, which can make the palate seem somewhat silky. The flavors are more intense and concentrated, but still should be appealing. Discerning tasters should appreciate how a cleanly-fermented beer with concentrated flavors does not become a fault-ridden trainwreck.
Brewing Ingredients and Methods
I won’t really go into depth on brewing an eisbock (doppelbock) since this style is mostly about the concentration process. The base doppelbock grist usually is heavy in the Munich and dark Munich malt, but other malts are common. Pilsner and Vienna malts can be used to cut the richness of the Munich malt. Medium crystal malts can be used to add more depth to the sweetness and bring in some additional dark fruit flavors. Aromatic malt can be used to boost the malt presence. Decoction mashes are traditional but I’ve also made this with an infusion mash, usually with a bump up in the dark Munich malt. Avoid heavily toasted or roasted malts.
Hops are usually just in the bittering, with German noble hops the common choice. A clean bittering hop like Magnum is also a good choice. Low mineral water or water with a light amount of chlorides is fine; anything that isn’t heavy in carbonates and sulfates should work. The yeast should be a clean and neutral lager strain, with low sulfur production. I sometimes use WLP833 (German Bock) yeast in bocks, but here I think it would make the beer too rich and malty. Something a little more attenuative is needed. A normal lager fermentation schedule should be followed, keeping fermentation temperatures cool and lagering for a couple months.
Let the doppelbock finish lagering to clear and clean up any fermentation byproducts. Now you can evaluate it prior to the eisbock process. Do not carbonate the beer yet. Just check that the beer tastes good, doesn’t have any serious flaws, and no longer tastes green. If it does, let it continue to lager. Otherwise, rack it into a purged keg and we can get started.
Before I explain how I concentrate an eisbock, a note about equipment. I normally lager in a keg because I need to use my lagering fridge for this step. I’m using a converted freezer with a temperature controller, so I am able to adjust the temperature accurately. This is important for the process. Don’t use glass fermenters as they can crack or shatter.
With my keg in my temperature-controlled freezer, I set the temperature to around 28 °F (-2 °C) and let the keg begin to freeze. I check it every few hours by gently rocking it, checking for a slushy sound and feeling. We don’t want it to freeze hard, so I don’t recommend sticking it in a snowbank overnight, regardless of folklore. Once at the slushy phase, it’s time to transfer. Don’t let it freeze too much (though if you do, you can always allow it to thaw partially).
There are other ways of doing this. I have heard other brewers let the keg fully freeze, and then thaw the beer, collecting as it melts to reach the desired target volume (and hence, concentration). Others will put the keg just a few degrees below freezing, say 29 °F (-1.5 °C), knowing that the alcohol has a lower freezing point. After a day, remove whatever liquid portion remains, sample, and then lower the temperature another degree if further concentration is desired. Repeat the process until the target volume has been collected. There is some manner of trial-and-error or repeated adjustment in all three methods. Chill out (heh).
I use CO2 to push the beer into a clean, purged keg, watching the transfer line for signs of cloudiness. I try to push only clear beer. Note that you are basically taking a guess about how much water has been frozen from the beer. We will measure the actual concentration after we are finished.
Once the beer has been transferred, the target keg can be lagered for additional time to condition. I normally check the frozen keg to determine how much water was removed. Let it melt, then measure the volume. I aim for 20% concentration, or about a gallon (3.8 L) of water removed from a 5-gallon (19-L) batch. The target keg can now be carbonated, and enjoyed after it has aged enough to smooth out the alcohol.
Homebrew Example
My eisbock is really just my normal doppelbock recipe, with the eisbock concentration technique. I know some people say to brew a different type of doppelbock, but I don’t. Or maybe I don’t aim to brew an overly malty doppelbock to start with. Either way, I’m happy with this beer as a doppelbock, but I also think it makes a great eisbock.
I prefer my doppelbocks to not be super sweet or heavy. It’s still a German lager, after all, and I want to be able to drink a fair amount of it. So, I shoot for a malty palate with rich flavors, but a dry finish.
I like to use a double decoction with my doppelbock, but, as I mentioned earlier, I did recently make it at a commercial brewery using a single-infusion mash because of the system. So, this recipe reflects that version, except it has my original hop and yeast choices. Really, the hops can be any noble-type variety; in my commercial version, I used Magnum. Just for fun, I tried the Mexican Lager yeast, and found that I really liked the low sulfur, clean and malty palate, and dry finish of it. Any lager yeast with a similar profile is likely to work.
I use the concentration method outlined in the article. Having a temperature controller on a freezer or some other method of accurately controlling temperatures around freezing is the key, as well as having the necessary kegging equipment to conduct the transfers. Pay attention during the freezing process, this should take hours, not days. Maybe smoke a brisket or a pork shoulder while this is going on. You need a similar amount of attention to the process. Give the finished beer additional time to smooth and mellow out, basically lagering it again. Time is your friend here, so be patient and you will be rewarded.
Eisbock by the Numbers:
OG: 1.078–1.120
FG: 1.020–1.035
SRM: 17–30
IBU: 25–35
ABV: 9–14%
Eisbock
(5 gallons/19 L, all-grain)
OG = 1.081 FG = 1.017
IBU = 21 SRM = 20 ABV = 8.4% (before concentration)
Ingredients
5 lbs. (2.3 kg) Pilsner malt
5 lbs. (2.3 kg) dark Munich malt
4.5 lbs. (2 kg) Munich malt
1 lb. (454 g) Carapils® malt
1 lb. (454 g) CaraMunich III malt
1 lb. (454 g) Caravienne malt
8 oz. (227 g) crystal malt (80 °L)
3.5 AAU Crystal hops (60 min.) (1 oz./28 g at 3.5% alpha acids)
3.5 AAU Tettnang hops (60 min.) (1 oz./28 g at 3.5% alpha acids)
Wyeast 2206 (Bavarian Lager) or White Labs WLP940 (Mexican Lager) yeast
Step by Step
This recipe uses reverse osmosis (RO) water. Adjust all brewing water to a pH of 5.5 using phosphoric acid. Add 1 tsp. of calcium chloride to the mash.
Mash in Pilsner and Munich malts at 152 °F (67 °C) and rest for 60 minutes. Add remaining malts, begin recirculating, and raise mash temperature to 168 °F (76 °C) by direct heat or infusion with boiling water and rest for 15 minutes. Rest at mashout temperature for 20 minutes while recirculating. Sparge slowly with 170 °F (77 °C) water, collecting 6.5 gallons (24.5 L) of wort.
Boil the wort for 90 minutes, adding hops at the times indicated in the recipe.
Chill the wort to 48 °F (9 °C), pitch the yeast, allowing temperature to rise to 50–52 °F (10–11 °C), and ferment until complete. Rack and lager for eight weeks at 32 °F (0 °C).
Rack to a clean keg and move to a temperature-controlled fermentation chamber. Lower the temperature to 28 °F (-2 °C) and check every few hours until the beer sounds slushy when gently shaking the keg. It should be ready within a day or so. Do not allow the keg to completely freeze. The goal is to transfer about 4 gallons (15 L) of beer, leaving 1 gallon (3.8 L) of ice behind.
Prepare a second clean keg. Connect the kegs using a short ‘jumper’ hose between the two beer side posts of each keg. Using a gentle pressure of CO2, push the concentrated beer from the frozen keg to the fresh keg. Watch the transfer and stop when cloudy particulates are seen in the transfer line. Lager the new keg for up to six months to smooth flavors.
Force carbonate in the keg. I’m not sure enough viable yeast will be left to bottle condition, which is why I recommend kegging eisbock. More yeast, in addition to priming sugar, would need to be added if you chose to bottle condition.
Eisbock
(5 gallons/19 L, extract only)
OG = 1.081 FG = 1.017
IBU = 21 SRM = 20 ABV = 8.4% (before concentration)
Ingredients
8.25 lbs. (3.7 kg) Munich liquid malt extract
3 lbs. (1.4 kg) Pilsner liquid malt extract
3.5 AAU Crystal hops (60 min.) (1 oz./28 g at 3.5% alpha acids)
3.5 AAU Tettnang hops (60 min.) (1 oz./28 g at 3.5% alpha acids)
Wyeast 2206 (Bavarian Lager) or White Labs WLP940 (Mexican Lager) yeast
Step by Step
Use 6.5 gallons (24.5 L) of water in the brew kettle; heat to 158 °F (70 °C).
Turn off the heat. Add the malt extracts and stir thoroughly to dissolve completely. You do not want to feel liquid extract at the bottom of the kettle when stirring with your spoon. Turn the heat back on and bring to a boil.
Boil the wort for 60 minutes, adding hops at the times indicated.
Follow the remainder of the all-grain recipe instructions.
