By Jack Horzempa
Homebrewers typically start off by making ales. This is because craft beer is mostly associated with ale styles but also likely because beginning homebrewers view the lagering process and the temperature considerations involved (e.g., cooler fermentation temperatures and the need for a cold conditioning) as too complicated. But making lager beers can be a fun thing to do.
To paraphrase some lyrics from a Talking Heads song: And you may ask yourself, "Well, how did we get here?"
The very first lager beers were produced sometime in the 1400’s in Central Europe in the area that is now present day Southern Germany and the Czech Republic.
What made lager beer unique was that it was fermented with a cold tolerant type of yeast. Yeast was not known to be a microorganism until much later thanks to the studies of Louis Pasteur in the 1800’s. As it turns out these lager beers were fermented by a species of yeast now known as Saccharomyces pastorianus, with the term “pastorianus” as an honor to Louis Pasteur. Saccharomyces pastorianus is a hybrid of Saccharomyces cerevisiae (ale yeast species) and Saccharomyces eubayanus; how exactly this hybridization came to be is still a matter of scientific study.
Sometimes Saccharomyces pastorianus has been referred to as a ‘bottom fermenting’ yeast but based upon my observations of the fermentation of lagers in my homebrewery I do not put much weight in this description. I find that my lager beers develop a krausen (foamy head) on top just like my ales and while the fermentation action may be a bit more subdued due to the colder temperatures, they look similar to me.
There are some additional differences between Saccharomyces pastorianus and Saccharomyces cerevisiae beyond just the cold vs. warm aspect:
Refrigeration was not invented until the latter half of the 1800’s so cooler fermentation and cold conditioning was managed via seasonal brewing and in the case of lagering sometimes using ice. In 2019 I took a tour of the Pilsner Urquell brewery in Pilsen, Czech Republic, and they still produce Pilsner Urquell the old way via fermenting and lagering in the cellars beneath the brewery. Below is a photo of an open fermenter and you will see in chalk this beer is being fermented at 5 °C (41 °F) which is quite a cold temperature for lager fermentation:
Below is a photo of a beer being poured from a lager barrel (made out of oak and lined with pitch). The Pilsner Urquell cellar brewed beer is lagered at the same temperature that the beer is fermented (i.e., 41 °F) for a duration of approximately 30 days.
Traditionally lager beers were produced in Germany (e.g., Bavaria) by placing the barrels of beer in cool/cold caves or cellars. To help maintain the cool temperature, blocks of ice which had been harvested during the winter, might be added to the caves. These beers would be stored in these conditions during the warmer months of the year and be made available for consumption throughout the summer and into the next fall.
In the mid-16th century, the Duke of Bavaria Albrecht V decreed that beer could not be brewed during the warmer/hot times of the year since brewing under these conditions often resulted in beers of poor quality. Under Albrecht’s decree, brewing was only permitted from St. Michael’s Day (September 29th) to the feast of St. George (April 23rd). The beers consumed during the summer and early fall therefore had to be produced in the winter/late spring months.
As a homebrewer I am of the opinion that the fermentation step is the most important phase of producing beer. If a beer is improperly fermented then no subsequent steps can ‘save’ the beer. While conducting a fermentation of a lager beer is on the surface very similar to fermenting an ale there are some other considerations. One often mentioned distinguishing feature of lager yeast strains vs. ale yeast strains is that they produce beers with a comparatively more neutral yeast produced flavor. For example, lager yeast strains typically produce significantly lower levels of esters (which contribute fruity flavors).
The differences in lager yeast strains are not as varied in comparison to ale yeast strains but they need to be carefully considered nonetheless. Some lager yeast strains, per the yeast vendor descriptions, will enhance the malt qualities of the beer while other strains will highlight hop flavor expression and the perception of crispness to the beer. How these aspects are perceived in the final product will also be a function of the wort. For example, in producing a malt forward lager such as an Amber Oktoberfest beer you would want to produce a wort using darker malts such as Munich Malt and then ferment that beer using a lager yeast strain that augments the flavor perception of malty. In contrast if you what to produce a lager such as a German Pilsner you want lighter malt/wort and a lager yeast strain which enhances hop flavor and crispness.
As with fermenting an ale it is prudent to follow the yeast vendor’s recommendation for fermentation temperature which will be further discussed.
The rule of thumb for fermenting a lager is to use twice the amount of yeast as you would for fermenting an ale. Part of this rule is a consideration that when fermenting cool (e.g., 45 – 55 °F) yeast metabolism is slower so more yeast cells is beneficial to conduct a robust fermentation. In my homebrewing practice when producing moderate gravity lagers (e.g., OG of around 1.050) using a liquid yeast from a vendor such Wyeast or White Labs, I produce a 2 liter yeast starter (with intermittent shaking) and this works for me. Another option is to pitch multiple liquid yeast packs. Fermentis recommends using two sachets when pitching their lager dry yeast products (e.g., W-34/70).
As with ales, if you are producing a higher gravity lager (e.g., a Doppelbock) you should increase your pitch amount accordingly.
It is important to properly aerate/oxygenate the wort since a lager fermentation is ‘stressed’ via the cooler temperatures; it is important to take all steps necessary for a healthy fermentation.
The same is true as regards proper yeast nutrition. Do not forget to add yeast nutrient in the kettle towards the latter part of the boil.
As has already been mentioned a lager is traditionally fermented cooler than an ale. Having stated that there are some lager yeast strains which are reported to be more tolerant of fermenting warmer (further discussed later in this section).
It is my personal practice to ferment lagers within the yeast vendor’s recommended fermentation range. I recently produced two lagers (Czech Dark Lager and Bohemian Pilsner) using White Labs WLP802 (the Czech Budweiser Budvar yeast strain). White Labs lists the recommended fermentation temperature range as 50 – 55 °F. For both batches I conducted the primary fermentation in the low 50’s °F. I maintain a steady fermentation temperature during the entirety of the primary but some brewers may prefer to utilize a varying temperature schedule. For the interested student some further reading on lager fermentation temperature profiles:
While I have no personal experience with producing lager beers via a warm (e.g., 68 °F) fermentation I have some knowledge here. I attended a presentation at HomebrewCon 2019 where a Fermentis person (José Pizarro) presented data (both experimental and sensory testing) that W-34/70 can be used to ferment warm and still produce a beer with lager characteristics. I have also watched videos where folks fermented warm with Wyeast 2124 and those beers were described as having lager characteristics. I find this information to be convincing.
One manner in which homebrewers maintain cool fermentation conditions is using a freezer or refrigerator with an external temperature controller set to an established temperature setting. Below is an example of a temperature controller which can be used to maintain a cool fermentation temperature:
My technique for fermenting my lagers in cool conditions is to ferment during the winter months in my unheated half-basement; my basement maintains an ambient temperature in the low 50’s. I also place my fermenter (a plastic bucket) on the concrete floor which functions very well as a heat sink (removing the heat from the fermenter).
The rule of doubling mentioned above for yeast pitch amount also applies to fermentation time. To ferment a lager generally requires about double the length of time for an ale. As an example, I have gotten into the habit of brewing on weekends. I will brew my lager beer on a Saturday and wait two weeks until that Saturday to transfer to a secondary for lagering. A variable here is the OG of the wort with higher gravity beer maybe needing more time to complete fermentation.
When fermenting lagers a diacetyl rest is typically recommended towards the end of primary fermentation. There is an article which discusses this in more detail:
https://www.morebeer.com/articles/Diacetyl_Rest
I will confess something: I have homebrewed a lot of lagers (I estimate 80+ batches) and I have never conducted a diacetyl rest. I find that if you just conduct a healthy primary fermentation and give it enough time in the primary (e.g., two weeks for a moderate gravity lager) the yeast will properly ‘clean up’ any diacetyl that was produced during the primary fermentation. But every homebrewer is different and every homebrewery is different so my suggestion is a diacetyl rest is perhaps good ‘insurance’ for others.
From my perspective a primary fermentation is completely finished when two conditions are met:
When I decide to package my ales, it is critical to achieve both of the above. But what about when producing lager beers? When producing lager beers there is the extra next step of cold conditioning beyond just a primary fermentation so there can be some wiggle room here.
I have a preference to not let my beers in the primary ‘sit’ on the yeast too long. While in all probability I will not necessarily perceive the effects of yeast autolysis here I prefer to remove the beer from yeast in a timely manner. Having stated that I also do not want to move the beer before the yeast has cleaned up undesirable fermentation byproducts like diacetyl (I strongly dislike diacetyl which taste like butter for my palate) and acetaldehyde. In my homebrewery I have consistently found that two weeks is sufficient time for the yeast to process both diacetyl and acetaldehyde to be below the taste threshold.
I have noticed that after lagering is complete the specific gravity reading may drop a point or two from the reading I take when I transfer the beer.
My recommendation is that your beer is ready to be transferred to the lagering vessel when both diacetyl and acetaldehyde is no longer perceptible (e.g., taste the beer from your hydrometer sample) and when the specific gravity reading is very close to your expected final gravity goal; make your specific gravity reading be the deciding factor vs. the calendar.
Heretofore the discussion was solely concerning making lager beer but there are some ales which are traditionally lagered as well. Two types of ales that I homebrew regularly which I also put though a cold conditioning phase are Kölsch and Altbier. These German ales are traditionally cold conditioned. I have found these beer styles do indeed benefit from a lagering phase. For the beers I have brewed I have found that the length of lagering and the lagering temperature is less stringent than needed for my lager beers. Just a couple/few weeks seems to work well and I have even lagered at cellar temperature (e.g., 50 °F) to great effect. Another 'trick' I have done which works for me is that I permit the beers to complete fermentation and then the bottle conditioning phase and just lager for a couple of weeks afterwards within the bottle. These batches taste great for me.
After the completion of a healthy lager fermentation, we can now proceed to the lagering (cold conditioning) phase.
Lagering vessel choices
Since the beer will be sitting for a period of time an important thing that is needed is a lagering vessel which is impermeable (or nearly impermeable) to oxygen. Oxygen is the enemy of beer since beer going stale is in large measure due to oxidative reactions. It may be counterintuitive but just because a material is solid does not mean oxygen cannot permeate through it. As a case in point the plastic that is used to construct fermentation buckets is made of HDPE (High-density polyethylene) which is permeable to oxygen; over a period of several weeks oxygen will ingress through the material and affect the beer inside the bucket (i.e., oxidation). During primary fermentation this is a lesser issue since the oxygen will get ‘scrubbed out’ during the active carbon dioxide production/outgassing but during the lagering phase this oxygen ingress is a problem.
Oxygen impermeable materials for lagering vessels are glass (e.g., glass carboy), stainless steel (e.g., corny keg) and plastic carboys constructed of a special PET (polyethylene terephthalate) plastic, which while not 100% impermeable, for plastic they greatly mitigate oxygen ingress.
Another important aspect of the lagering vessel is that it be completely filled to reduce air (oxygen) in the headspace. A 5 gallon batch of beer needs a 5 gallon vessel that should be filled to the top.
While a glass carboy has the advantage of being relatively inexpensive and 100% impermeable to oxygen it is a fragile vessel and when broken the shards of glass can be very dangerous. If you choose to use glass carboys make sure extreme caution is exercised with the awareness that an accident (broken carboy) could occur. During handling wear protective clothing such has heavy duty boots, heavy duty long pants and long-sleeved shirt, gloves, etc. Use a heavy-duty plastic milk crate to carry/move the glass carboy.
A plastic carboy made out of special PET (e.g., Better Bottle, Vintage Shop. Etc.) is a safer choice than glass. But since a plastic carboy is more prone to scratching any cleaning is best done using a soft rag inside the carboy; a stiff brush is not recommended for cleaning. A special PET carboy is not 100% oxygen impermeable but is sufficient for lagering a beer.
A more expensive choice for lagering is a corny keg which presents some options. Some homebrewers prefer to lager their beers in one corny keg then at the completion of the lagering phase transfer to a serving keg to get the beer off the residual yeast/sediment. This requires two corny kegs and carbon dioxide to force carbonate the beer in the serving keg. If instead the same corny keg used for lagering is also used for serving, a spunding valve can be attached to the keg to foster natural carbonation. A spunding valve is in essence a pressure relief valve which can be set to achieve a certain pressure before outgassing. The concept is to transfer the beer from the primary when there is still a little bit of residual extract to the beer and over time the yeast will complete the final stages of fermentation while simultaneously carbonating the beer and lagering.
Once the beer is transferred from the primary fermenter to the chosen lagering vessel the beer needs to be taken down to a selected lagering temperature. Some homebrewers choose to do this very slowly; something like decrease by 5 °F per day until the selected lagering temperature is reached. Other homebrewers, like me, choose to cold crash to reach the lagering temperature more quickly. Since I make my lagers in the wintertime my cold crashing process is fairly simple – I simply place my carboy on my brick patio for about 8-10 hours and let the cold temperature provided by mother nature to do the job. This process works very well for me.
The general concept for lagering is to condition the beer at or near freezing temperature (32 °F). Freezing cold is colder than what the German brewers would have achieved in their lagering caves and it is colder than Pilsner Urquell uses to lager their cellar brewed beers (i.e., 41 °F). During a tour of Únětický Pivovar in the Czech Republic I saw the control panel for their lagering process and the typical lagering temperature at that brewery is 2 °C (35.6 °F). In my homebrewery I choose to lager at 38 °F and this temperature works for me.
There are two basic considerations in play when it comes to the lagering phase:
A balance of sorts needs to be achieved with the two items above in that the colder the better for optimizing precipitation but too cold and the yeast activity is greatly slowed which impacts yeast induced flavor maturation.
These topics will be further discussed in the companion article entitled:
Now we come down to the $64,000 question (only you old folks will remember that TV show reference): how long do we need to lager our beer?
There is no one answer to that question since there are many variables in play here:
In the book “New Brewing Lager Beer” Greg Noonan suggested that lower gravity beers should be lagered for something like 3 - 7 days for each 2 °P of the OG of the beer. As one example, for a 1.040 (10 °P) beer a lagering duration of 15 – 35 days is needed. For mid-higher gravity beers, he suggests 7 – 12 days per 2 °P. For example, for a 1.048 (12 °P) beer 42 – 72 days of lagering would be suggested. A notion that more time should be devoted for lagering higher OG beers is evident here.
During my visit to the Czech Republic I toured a number of breweries and their practice is to lager for one month.
It seems to me that the rules established by Greg Noonan are quite conservative. For the past couple of years I have chosen to lager my moderate gravity beers for a month and this duration works for me.
I will further discuss aspects related to lagering duration in the companion article The Science of Lagering.
I previously discussed kegging beer with two options being to transfer from the lagering keg to a serving keg with the benefit of removing the beer from yeast/sediment. Or you could spund within the lagering key with the benefit of achieving natural carbonation.
I choose to bottle my lagers and a question that often comes up is whether there is enough yeast in the beer for bottle conditioning to occur. I can report that for my homebrewing practice there is always a sufficient amount of yeast in the lagered beer to permit bottle conditioning to take place. One thing I do is permit additional time in the bottle for a total of three weeks of bottle conditioning at room temperature. For folks who are a bit nervous in this regard, you could choose to add some additional yeast into the bottling bucket with any neutral ale yeast strain being an acceptable choice here; this is especially a good idea for higher gravity lagers (e.g., Doppelbocks). I would also suggest that additional time in the bottle would be beneficial for higher gravity lagers.
Now, go out and make some lager beers!
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