The Warm Lager Method


by Dr. Mickie Willis (Brewing Techniques)

How to Brew Lager Beer at Room Temperature


Can you brew a lager at room temperature?


With the help of insights gained from acoustical theory, one brewer discovered a simple method of brewing crisp, clean lagers at room temperature.



I suspect most home brewers brew more ales than lagers because of the limitations in their household work spaces rather than because of their drinking preferences. Although the popularity of home brewing has increased interest in a greater variety of beer styles, particularly ales, over the past 20 years, beer sales suggest that most Americans prefer lagers. How many more of us would take up lager brewing if it were possible to brew good, clean lagers in our kitchens, without any means of refrigerating the fermenting vessels?

Despite the conventional wisdom that fermentation must be carried out under refrigeration, it is reasonably easy to create crisp, clean lagers, free of the esters, diacetyl, and fusel alcohols that so often mar our efforts to duplicate some of the world’s best beers. The methods presented here are the result of some simple innovations in my home brewery, inspired by the basics of acoustic theory as applied to speaker construction (see box).


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Challenging a Cool Tradition


Much of the difference between ales and lagers is caused by the strain of yeast, of course, but even the best lager yeasts will produce ale-like flavors if allowed to ferment too warm. The traditional strategy for containing this activity (probably discovered accidentally and empirically reinforced) has been to conduct fermentation at cool temperatures (40–55 °F). Good results can be obtained, however, even if temperature is kept low only during kräusen and then allowed to rise to room temperature levels later in the fermentation! While it may be difficult or impossible for home brewers to keep fermentors cool during the entire fermentation process, especially during the summer months, it is easier to keep them cool at the beginning of fermentation — the most important time to keep temperature in check!

Although large batches are typically more difficult for home lager brewers because they are more difficult to keep cool, in this case the larger the batch, the better; thermal inertia slows the gradual rise to to ambient temperature. The rise to room temperature can be further slowed by using an insulated fermentor such as a doubled-walled plastic water cooler. A 10- or 15-gal batch in a well-insulated cooler will take several days to reach ambient temperature. By this time, the most critical time of the creation of unwanted fermentation by-products will have passed. In fact, elevation of temperature late in fermentation is a tactic often used by commercial breweries (most notably in Germany) to help boost the activity of yeast strains that do not easily reduce diacetyl levels produced during kräusen. In this way, brewers effectively damp the most active phase of the process — the fermentation “resonance” (see box) — by deliberately making conditions less conducive to yeast activity at the time when it is most energetic.


Borrowing Lessons from Acoustical Theory

What does brewing have to do with acoustical theory? After all, acoustics involves the mechanical behavior of sound, and brewing involves biological processes. The two share one interesting trait: Both work with uneven energy outputs that must be contained for one reason or another, and both require the careful management of natural tendencies.

Audio engineers, for example, need to design speaker systems that have the most linear audio output possible over the entire range of human hearing. An acoustical driver (speaker), for example, and the air captive inside its enclosure (both the box in which the speaker is enclosed and the room or auditorium into which it plays) vibrate more efficiently at some frequencies than at others. This varied efficiency causes electrical energy input to result in more acoustic output at some frequencies than at others. Uneven response is characteristic of poor speaker systems and is the root of the phrase boom box, now applied to large portable stereos.

Audio engineers and acousticians use the term Q to describe the degree of magnification at resonance of a speaker, speaker system, or other vibrating body. The higher the magnification, the higher the value of Q. We’ve all experienced the effect of high-Q resonance while singing in reverberant environments such as showers, which magnify a narrow range of frequencies (often 70–200 Hz) and makes even the weakest male voice seem rich and powerful. It is the challenge of high-fi speaker designers to design enclosures that damp this magnification at resonance — the speaker system Q — so that the response is as uniform as possible.

Lager brewers too must damp a resonance of sorts to achieve smooth, clean flavor. For us, the high-Q resonance of fermentation is the period of most intense yeast activity, which occurs for the first several days after the lag period. We call this the respiratory, or kräusen, phase, and recognize it as a normal part of brewing. But most of the by-products of yeast metabolism that characterize ales — and that are undesirable in lagers — are formed during this time. Just as audio engineers damp excessive audio output from speakers by designing a box that inhibits the natural resonance of the speaker, so too can brewers effectively damp the most active phase of the fermentation process by deliberately manipulating conditions that are less conducive to yeast activity at the time when it is most energetic.

The analogy goes even further. Take, for example, the case of an unenclosed speaker that has a very high Q at a resonance of 100 Hz. A designer may calculate the dimensions of a box that contains a volume of air that resonates at a different frequency (perhaps 50–75 Hz), which would be out of phase with the speaker. Rather than reinforce the uneven response of the speaker, the box tames the unevenness. The two bodies, with their resonances at frequencies that inhibit each other, will couple to produce a unified sound output that is smoother over a broader range of frequencies than either alone.

In brewing, when we lower the temperature of the wort at the beginning of the fermentation and allow it to rise slowly, later in the process, the temperature curve is “out of phase” with the natural tendency of the yeast body. In the early stages of fermentation, when the yeast is naturally most active, we can inhibit it with low temperatures. Later on, when the yeast naturally tends to become less active, allowing the temperature to rise will increase its activity. Thus, the two factors combine to yield a smoother, more uniform rate of activity than would be the case without “out-of-phase” temperature manipulation. This temperature containment, in effect, becomes the “thermal box” that couples to the yeast activity.

The methods used by audio engineers to damp acoustical resonances and rid speakers systems of excessive behaviors provides an interesting lesson for brewers. By diminishing the natural unevenness of fermentation, brewers can produce excellent lagers at room temperature.


The strategy is to begin fermentation at a very high pitching rate, but at very cold Temperatures — around 40 °F. This flies in the face of conventional wisdom among home brewers, which recommends that yeast be pitched at a temperature somewhat warmer than its standard fermentation temperature and then gradually lowered to a cooler range. With proper pitching rates, however, fermentation will begin within 8–12 hours even at temperatures as cold as 40 °F.


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Procedures for Lagering at Room Temperature


My method for room temperature lager brewing begins with boiling a concentrated wort (whether extract or all-grain), chilling it with ice to near freezing for the best possible cold break, and racking off the trub. This procedure leaves only about 3–4 gal of clear, high-gravity wort (in a 6-gal kettle), to which I add water that has been chilled in my refrigerator. If the water in your area is not reliably free of bacteria, distilled water is cheap enough to buy in convenient 2-gal jugs, or you can preboil water and refrigerate before brewing day. I then pitch the yeast, usually at around 40 °F (4–5 °C). I then allow the fermentation to proceed undisturbed. Of course, the cooler the surroundings, the longer the temperature inside will remain cool, even in an insulated vessel, and the better the results.


Room-Temperature Lagering — A Quick Overview

Any good beer requires good brewing methods, such as proper pH in the brew kettle, adequate cooled-wort aeration, and the use of high-quality ingredients. To create a crisp, clean, clear lager at room temperatures requires some additional tricks and considerations.

  • Use honey as an adjunct (10–30%, depending on the desired dryness, the fermentability of the malt, and the attenuation of the yeast). The use of any adjunct in excess of 30% is unwise and will adversely affect flavor.
  • Use Irish moss 20 minutes before the end of the boil to help coagulate proteins.
  • Cool the wort as quickly and as near freezing as possible (for anywhere from 4–12 hours). Proteins removed at this stage can’t cause haze later. Plus, when proteins are removed before fermentation, they are unavailable to yeast in the production of fusel alcohol.
  • Rack the wort off as much of the hot and cold trub as possible. You will need to adjust your recipe to allow for the loss of as much as 30% of your wort after the boil.
  • Step up yeast to a starter of at least 1 L per 5 gal (2 L is better). Use only high-quality, liquid lager yeast.
  • After thoroughly aerating the wort, pitch cool (no, make that cold) at 35–40 °F (2–4 °C). Adding ice-cold water to cold concentrated wort is one convenient method of achieving such cold pitching temperatures. Use distilled or preboiled water unless you’re absolutely sure your water supply is safe from bacteria. The starter also must be at this temperature, or thermal shock will delay the onset of fermentation.
  • Ferment in the most insulated vessel you can find — 10 gal plastic water coolers are perfect. The bigger the batch, the better, because the increased mass will slow the rise to room temperature.
  • Unless you have a place to store bottles at near-freezing temperatures and are willing to wait for chill haze to settle out naturally, use a secondary fermentation, clarifiers, and force carbonation (in kegs or bottles). It is important to give the beer a secondary fermentation before clarifying because clarifiers such as Polyclar, when used aggressively enough to completely haze-proof a light lager, will also remove so much yeast that the beer will cease to attenuate or reduce diacetyl and will be more susceptible to infection.


Once fermentation is under way, I avoid opening the fermentor for such activities as hydrometer readings and skimming, which only accelerate warm-up and increase the risk of infection. Instead, I rely on the bubble rate in the closed fermentor to indicate the beer’s progress.

Bottling: If I plan to bottle the beer, I conduct single-stage fermentation and bottle directly from the primary fermentor after 12–14 days. I allow the bottled beer to condition and attenuate further for 7–10 days at room temperature and put it in a refrigerator to chill and precipitate and settle the haze. (Without clarifiers, bottle lagering is necessary to eliminate the chill haze. I believe clarifiers are best used when the beer is to be artificially carbonated.) This three-step process typically takes a month or more, after which the lager is at or near its peak. (My wife is splendidly tolerant of my keeping up to 10 gal of beer in our refrigerator — of course, she enjoys it too!).

Kegging: If I plan to keg and force-carbonate, I transfer the beer to a secondary fermentor after 10–12 days and allow it to attenuate and reduce diacetyl. After about 10–14 days in the secondary, I add Polyclar (polyvinyl pyrrolidone) and silica gel to clarify the beer a couple of days before kegging. The beer can be force-carbonated and drunk almost immediately. Total turnaround time for the kegging method is about three to four weeks for completely clear, finished beer versus six weeks or more for the naturally carbonated, bottled version. It is worth noting that adding clarifiers before kegging accomplishes much of the same result (except attenuation) as extended lagering. In addition to precipitation and settling of haze producing molecules, the clarifiers draw out tannins that detract from the beer’s flavor (this happens with cold storage, but at a much slower rate).

I personally do not agree with the common belief that chill haze is tasteless. There is no doubt that a beer tastes the same whether or not haze is visible (except, of course, the difference in flavor that results from serving the beer at different temperatures). But I believe chill haze compounds do contribute to flavor (or, detract from it, depending on your point of view). A beer that is clear at 35 °F (1–2 °C) definitely tastes different from the same beer that has haze-causing compounds present — even if these compounds are invisible at warmer temperatures. If a pure, clean lager is your favorite beer, then haze removal — using either clarifiers or a traditional lagering method — is a must.

Use of adjuncts: One other element can contribute significantly to the success of lagers brewed at room temperature — the use of an appropriate adjunct. Before you reject this suggestion immediately, citing the Reinheitsgebot, remember that some outstanding lager beers brewed outside of Germany (and now even a few inside Germany) make use of adjuncts. Despite the widespread notion that good beers can be brewed by using malt only, there is good reason to incorporate simple sugars into the process. One of the features of lagers, especially Pilseners, is a high degree of attenuation. When mashing, this means that the mash temperature is usually held relatively low — 150 °F (65 °C) — so that beta amylase enzymes convert more starch into shorter chain sugars, which are fully fermentable, resulting in a drier, crisper beer. Why use expensive malt to make simple sugars that ferment out completely and contribute nothing to flavor but do contribute to chill haze?

I prefer to mash at higher temperatures to contribute malt flavor and make up the remainder with adjuncts. (An alternative is to use an extract such as Laaglander dry extract that has a relatively higher proportion of more complex sugars.) All adjuncts, however, are not alike. Although the most common ones are fully fermentable, some are more readily fermentable than others. In this respect, light honey stands out as a superior adjunct. It attenuates as completely as corn sugar but at a slower, more uniform rate, making it the ideal choice for lagers, especially Pilseners. Because it has a somewhat slower rate of fermentation, light honey helps keep initial fermentation subdued; remember, this is when many of the “non-lager” flavor compounds are created.


It’s Easier Than You Think


By rigorously following good brewing practices and borrowing a lesson from the methods used by audio engineers to damp acoustical resonances and rid speakers systems of excessive behaviors, home brewers can diminish the natural unevenness of fermentation and successfully brew excellent lagers with nothing more than a water cooler and a refrigerator.

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