By Jim Busch (Brewing Techniques)
Patience is required to master the complex process of lagering, but U.S. home brewers are embracing the technology to brew lagers every bit as clean and delicate as those of Europe.
This installment of Home Brewery Advancement begins a two-part series on some of the important processes required to lagering. This issue, I summarize the process of lager brewing. In the next issue, I will explore the chemistry and art of the lagering process.
Lagers are very different from ales in recipe formulation, brewhouse processes, and the all-important temperature-controlled fermentation and lagering. Lagers are much less forgiving than ales because they are delicate, clean, and balanced. Fruity esters, hot higher alcohols, and the huge bittering levels often found in ales are usually avoided in lagers.
Good lagers are hard to find in the United States, and until recently it was rare to find many home brewers who understood the subtleties of lager brewing. This situation is changing as craft brewers become more capable of producing world-class lagers and the home brewing community becomes more technically oriented. This series explores how to successfully brew great lagers at home.
Most first-time brewers focus on ales; only after one becomes fairly experienced does the extra effort involved in brewing lagers seem reasonable. Lagers are more complex and take more time to prepare. The lagering process occurs over weeks and only after the completion of primary fermentation. Lagers also require higher pitching quantities of yeast than do ales, and the choice of yeast strain is at least as important as it is for ales. Brewhouse procedures that minimize oxygen pickup are even more important for pale lagers than for ales. In addition, careful temperature control during the fermentation and lagering periods is essential. For all of these reasons, lagers are hard to make well and are best reserved for more experienced brewers.
Some definitions: The German word lager literally means “to store.” Practically, it defines a style of beer that is fermented by S. uvarum (or S. carlsbergensis, after the historic research performed on lagers at Carlsberg Brewery in Denmark). Lager yeasts are often termed “bottom-fermenting,” but this is misleading because S. uvarum does not ferment on the bottom (nor does ale yeast ferment on the top). Instead, the yeast tends to flocculate (drop from suspension) toward the bottom of the fermentor (and with ale yeasts toward the top) as the beer consumes the fermentable sugars. Lager yeasts ferment some complex sugars that ale yeasts cannot.
Lagering is the process by which lager beer is aged for extended periods at cold temperatures. Strictly speaking, lagering occurs after the completion of fermentation. In unitanks, primary fermentation yeast is dropped and discarded at the conclusion of primary fermentation. In most home brewing conditions, the beer is racked off the primary yeast and allowed to lager in a separate vessel such as a Cornelius keg or a closed carboy. Six weeks is a typical lagering period for a traditional Pils-gravity beer (12–13 °P); 12 weeks or more is typical for a 20 °P Doppelbock.
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Malt: Typically, lagers brewed at home include Märzens and Oktoberfests, Pils, Bocks, Helles, Exports, and Dunkels. While these beers have distinct recipe formulations, the common ingredient is usually European lager or Pils malts. Pils malts tend to have lower protein levels than their domestic counterparts and are somewhat less modified. Although a decent lager can be produced from a domestic two-row malt, a Pils malt (especially German Pils) will produce a more authentic version. (Skip the pale ale malts for lager beers — they have no place in well-formulated lagers.) Specialty malts should also be European types, because domestic specialties tend to be produced from six-row malt, raising the protein levels even higher than domestic two-row malt and often imparting elevated levels of tannins from the husk material. A portion of high-quality Munich malt, often in the 10–20 °L range, is recommended for true malty lagers.
Water: Water chemistry is another area of great concern to lager brewers. While the water supplies of classic lager brewing towns fluctuate widely in mineral levels, a general rule is to minimize sulfates. In general, avoid the use of gypsum (calcium sulfate) in lagers. If calcium ions are desired, try calcium chloride instead. If you use high-sulfate water, it is better to use reverse-osmosis (RO) or distilled water to reduce the alkalinity and mineral content. A low mineral content is particularly important when brewing Czech Pilseners such as Pilsner Urquell; the water should be extremely soft, and only RO or distilled water will be able to approximate this effect in most regions.
The mash: Mashing for lager beers is usually more involved than mashing for ales. Most lagers are brewed using an upward step mash program. In this program, the first step is to dough in at around 104 °F (40 °C) for a beta glucan rest, or directly to 122 °F (50 °C) for a protein rest. Depending on the degree of modification of the malt, this rest could be as short as 10–15 minutes (for highly modified malts) or closer to 30–45 minutes.
The next step typically occurs at 140–145 °F for 10–15 minutes, the optimum range for beta amylase activity and hence yielding the bulk of the maltose production. For very highly attenuated beers, this rest is extended to as long as 45 minutes, resulting in optimum production of easily fermented wort sugars and lower final gravities. Next, the saccharification rest is done between 152 and 158 °F (67 and 70 °C) for 30–60 minutes or until the mash is completely converted. A rise to 170 °F (77 °C) precedes lautering.
The mash program outlined above is typical for many lager beers but will not yield the intensely malty, rich, and complex beers that can be achieved using decoction mashing. The decoction system can make most lagers more complex; with some malts, it can produce a slight increase in extract.
For malty but light-colored lagers, a single decoction is sufficient. The decoction can be done to raise the mash temperature from protein rest to saccharification, or from saccharification to mash-out. In the latter case, an “in-kettle decoction” can be used, obviating the need for a dedicated decoction cooker. To do this, allow the saccharification rest to finish and then transfer roughly two-thirds of the mash to the lauter tun; bring the remaining third carefully to a boil. Continuous stirring is important to prevent scorching, especially in lighter colored beers. After a 20-minute boil, combine the two mashes and proceed with lautering.
Richly dark and malty beers such as Bocks require double or even triple decoctions. The decoctions are pulled, allowed to saccharify, and then boiled. The decoctions are pulled between the protein and saccharification rests (first decoction) and again to step from saccharification to mash-out (second decoction). A triple decoction, typical of the Urquell process, also uses a decoction to transit from the beta glucan rest to the protein rest. Needless to say, these many steps lead to a very long brew day (1,2).
Lautering: Lagers are lautered the same way as ales, although in German lauter tuns brewers often run rakes to keep the mash from compacting too hard on the filter plates. In home brewing, the mash can be cut with a long-handled spoon to help emulate this technique.
The boil and hop additions: Lager beers are also boiled in a traditional fashion; a 30-minute boil is desirable before the first hopping, and the complete boil time is often 90 minutes. Hopping techniques are very important in all beers, and lagers are no exception. Most lagers, with the important exception of Pils, are lightly hopped beers, in both aroma and bittering categories. If you want an intensely malty beer, keep the hopping level close to 20 IBUs. Higher alcohol beers can handle a bit more hops, but an upper limit of 30 IBUs is good for all but Pils beers.
Pils beers are a lager brewers answer to IPAs. The type of Pils that I love is the German-style Pils, intensely hopped with German and Czech low-alpha hops. Saaz, Hallertauer, Spalt, and Tettnang are all excellent choices, individually or as blends. U.S. substitutes are Liberty, Mt. Hood, and Ultra. In general, high-alpha hops should be avoided for lagers. Mid-alpha hops such as Northern Brewer and Perle are fine, and some very good lagers are made with Clusters, provided the total IBUs from them are less than 20. Such mid-alpha hops should be boiled at least 30 minutes.
Late hop additions for aroma purposes are rare; hops are seldom added less than 20 minutes from the end of the boil in traditional lager brewing. Dry hopping is even rarer.
Trub removal: Trub removal is important in all beers; in particular, removal of trub formed in the hot break. For lagers, cold trub removal is beneficial, especially for light-colored, low-hopped beers in which stable flavors are of concern. For most home brewers, cold trub removal involves chilling the wort into the 40s °F, allowing it to settle over several hours, and racking into a clean fermentor, leaving the trub behind.
A home flotation tank can also be devised in conjunction with an oil-less compressor used to inject filtered air inline with the wort or to bubble air into the fermentor. After several hours, the cold trub will be scrubbed to the top, and the brewer can carefully rack from under the trub. This procedure is probably not very practical for most, but it is the method of Old World German brewing. My own advice for home brewers is to first brew without cold trub removal and taste the results to see if it is detectable (3,4).
Yeast preparation: Lagers need lots of yeast, even more than typical ales. For a 5-gal batch, grow 3–4 L of yeast starter, allow this to fully ferment, and decant off the fluid, pitching only the yeast slurry. When growing up fresh lager yeast, the temperature of the starter culture should be gradually lowered until it reaches the final pitching volume. The first culture therefore can be done close to 65 °F (18 °C), but the last should be grown as close to pitching temperature as possible. Be sure to aerate the starter at each step.
Lager beers need to be fermented cool. Chill the wort to 45–48 °F (7–9 °C) before aerating and pitching the yeast. This is a real challenge for many home brewers because tap-water chillers can achieve only tap-temperature wort. Ice baths and in-line immersion ice chillers offer options for squeezing out an extra few degrees. Many brewers therefore can make lagers only in the cold winter months, just like the brewers of old.
One thing to avoid is pitching lager yeast when the wort is above 50 °F (10 °C). Unless a reliable chilling device is available for the fermentor, pitching above 50 °F can lead to ferments in the high 50s °F to low 60s °F, and this is not how good lagers are made — high-quality steam beers, perhaps, but not traditional lagers.
A temperature-controlled refrigerator is a natural choice for storing fermenting carboys or Cornelius kegs. Larger fermentors need to be fitted with a jacketed or immersion chilling system. Techno-gadget freaks should seek out high-quality temperature controllers or make them using the PC-based techniques.
Traditional lagers are fermented close to 48 °F (9 °C) for the duration of the primary fermentation. A sample of wort may be “fast fermented” separate from the main batch to test for degree of fermentability. To do this, keep a sample jar of wort with a large amount of yeast fermenting at a warmer temperature than the main batch. When this sample finishes, you can read the maximum attenuation of the main beer. If fermenting in pressure vessels such as Cornelius kegs, the vessel can be sealed when it is within 1–2 °P of final attenuation, which will naturally carbonate the beer.
Diacetyl rests: Some brewers use a diacetyl rest at the end of the primary fermentation, slowly allowing the temperature to climb from 48 °F (9 °C) to as high as 58 °F (14 °C). The temperature is held at this level for 1–3 days and then gradually decreased to accelerate the natural reduction process of the yeast. Another school uses a diacetyl rest closer to 42 °F (6 °C) for a few days and never allows the beer to rise above 50 °F (10 °C) during primary fermentation. The method you decide to use, if any, is largely dependent on the yeast strain selected and its propensity to throw diacetyl and subsequently reduce it. Strains such as Weihenstephan 34/70 are so clean that this rest is usually unnecessary.
At this point, the beer is fully (or nearly fully) fermented and the true lagering period begins. To lager the beer, slowly drop the temperature 2–4 °F per day until the beer reaches 31 °F (–1 °C) or as close to that temperature as possible. Allow the beer to lager at 31 °F (– 1 °C) for 4–12 weeks; generally, the longer the better. As periodic taste tests will reveal, the rough edge of the beer subdues and mellows over time. At some point, usually 2–6 weeks into the lagering, it is clear that the beer has changed into a smooth, malty, rich beer with little residual fermentation flavors such as diacetyl or sulfur. At this point, the beer is ready to be packaged.
Brewing good lagers is a difficult and unforgiving art, but a most-rewarding one when mastered. In the next installment, I will address more of the chemical changes that take place during lagering and explore some alternative lagering techniques.
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