Lagering - Is it worth the effort? George J. Fix
To the average homebrewer, the term "lager" is a descriptor for beer styles; namely numbers 12 (Bock) through 17 (Vienna/Maerzen/Oktoberfest) on the AHA category description list. The one common factor in these styles is the type of yeast used, and not the way they are processed. On the other hand, historically the reverse is the case, and a "lagered beer" has generally been one which has been afforded an extended cold maturation, independent of the type of yeast used. Arnold finds that extensive cold storage goes back to the very beginning of monastery brewing (approximately 50-100 A.D.), if not sooner. This possibly pre-dates the systematic use of what today is a genetically narrow band of microbes called lager yeast. However, this begs the absolutely fascinating open question of exactly when lager yeast entered monastery brewing.
In Bavaria lager beers were also called summer beers because they were brewed from September to April, and cold lagered during the summer months. When refrigeration was introduced near the end of the 19th century, brewing was possible year round. Yet the 3-6 month cold storage still found favor, and 6-9 month cycles were common for high gravity lagers.
An interesting twist occurred in the U.S. among ale brewers in the sense that early on extended cold storage was employed by them. Greves, an English brewer who visited the U.S. just before the turn of the century, commented on this point. He cited two reasons for this departure from traditional British ale brewing practice. First, he noted competitive pressure from lager brewers, who tended to promote the theme that beer clarity and beer purity were synonymous. Cold storage is one of the best ways to clarify beer, a point that is discussed below. Very likely these influences affected German ale brewers in the Rheinland as well. The second reason cited by Greves was the unfavorable climatic conditions in the U.S., and therefore the need for cold maturation to promote beer stability before distribution. Greves praised the overall quality of American ales, but he concluded that cold storage was not needed in the U.K.
One of the most obvious trends in brewing practice in the 20th century has been the gradual reduction of aging times. "Common beer" using short 2-3 week cycles have been present throughout this century, but it was not until the last part of the century that short cycles were used for premium products. Even Pilsner Urquel, argueably the flagship lager, has been affected by these trends. It was brewed on a six month cycle throughout much of the 20th century. This was cut to three months in the post World War II era, and it is now produced using cylindrical conical fermenters with a short brewing cycle. Critics of this trend cite competitive pressures, and a relatively flat beer market for putting a premium on plant efficiency. Lighter flavored beers were also increasing in popularity during this period. These beers tend to require less aging, the limiting case is water which requires none!
Defenders of short aging periods argue differently. First, given the increased understanding of beer fermentation that has occurred in the last few decades, it is now possible for brewers to reduce green beer characteristics in the main fermentation. In previous periods that was one of the main purposes of aging. Also, there has been vast improvements in yeast management as well as considerable improvements in the quality of brewing materials, most notably malt. These also reduce brewers dependence on aging.
As homebrewers we are free of many of the pressures facing commercial brewers. As a consequence, we can and do put beer quality above any other consideration. Thus, if extended cold storage will improve beer, it will be employed by most homebrewers. On the other hand, it makes little sense to cold lager beer beyond the point where improvements stop. This begs the central questions associated with this article. Namely, exactly what does cold maturation do for us, and how much is enough?
We shall define cold as below 2°C (36°F), although some of the mechanisms discussed below can also take place at slightly higher temperatures.
1. Beer Clarification
The most obvious benefit of cold maturation is the precipitation of haze active polyphenols and proteins. The cold conditions also encourages yeast flocculation. It is my experience that the beer should clarify within the first week of storage. This is possibly why two week cycles for ales, and three week cycles for lagers are so widely used in commercial brewing.
Failure to clarify during the first week of storage is usually due to technical errors. Poor quality malt and/or dysfunctional yeast are obvious culprits. Errors in mashing and sparging cannot be ruled out either. The solution in these cases is not to extend the aging period, but rather to correct original problem.
2. Chill Proofing
Extra measures are needed to chill proof beer. Additives like silica gels and polyclar can remove the relevant haze active constituents. I have found that extended cold storage (say 8-12 weeks) at 0-2° C (32-36°F) will achieve the same effect. The recently developed ice brewing procedure provides an interesting alternative. In this process beer temperature is reduced to just below its freezing point so that very small ice crystals are formed. Extensive data has shown that the beer obtained after separation from the ice crystals is fully chill proofed. In commercial practice, where this process is automated, the temperature is reduced to a couple of degrees centigrade below the beer's freezing point. The latter varies with alcohol content, but it is near -2.3°C, (27.9°F) for beers of normal strength. The contact time with the ice crystals is brief, typically less than one hour. In homebrewing higher temperatures and longer times are used. I have found that holding the beer at -3°C (26.6°F) for 48-72 hours is adequate.
3. Reduction of Diacetyl
The most widely studied green beer compound is undoubtedly diacetyl. There is good reason for this since it can be responsible for some highly unpleasant flavors, especially in packaged beer as it ages. There is ample evidence that the long extended cold storage, in contact with yeast, was the primary tool used by turn of the century brewers to combat off flavors like with diacetyl. In modern practice, there is a decided preference for reducing diacetyl in the main fermentation. This is achieved through proper yeast management, and in particular using yeast which have very low bacterial and mutant levels. It can happen at the fermentation end point that diacetyl levels are slightly above acceptable levels. In this case, best results are usually obtained by kraeusening the beer with fresh wort and yeast, rather than relying on extended aging.
It should be noted that there is much more to flavor maturation than reducing diacetyl levels. For example, research on immobilized yeast reactors has shown that diacetyl can be reduced to normal levels with only a few hours of maturation. Nevertheless, the overall quality of beers produced with these systems has not been impressive.
4. Reduction of Sulfur Compounds
Fermentations conducted at ambient temperatures 18-20°C (65-68°F) should end with all relevant sulfur compounds well below their threshold. Exceptions are usually due to infection by sulfur producing gram negative microbes. These can be found in infected wort and/or in pitching yeast. With lagers fermented at 8-12°C (46-50°F) the situation is more complex. First, the removal of volatile sulfur compounds in a cold fermentation is greatly reduced over what occurs at higher temperatures, and this can lead to a situation where several sulfur compounds are above their flavor threshold.
Lager brewers disagree about how much is too much. However, there is widespread agreement that lager beer will be insipid if all sulfur bearing compounds are reduced below their threshold. In addition, residual sulfur can act as an oxygen scavenger, and this may be responsible in part for the excellent flavor stability of traditional lagers. Nevertheless, most lager beer needs some maturation to reduce sulfur levels, and it has been my experience that objectionable sulfur levels can be reduced to acceptable levels within one week of storage at 0-2°C (32-36°F).
Failure to achieve this reduction can be due to several factors in addition to those cited above. A common culprit is high DMS levels in chilled wort, which may be due to the malt or wort production procedures used.
Yeast related issues tend to have more damaging effects. While there is a difference with respect to sulfur production among strains, pitching rate is even more important. Ideally, lager yeast should be pitched at a rate of 1-2 million cells per ml for each degree Plato; e.g., between 12 and 24 million cells per ml for 12°P (1.048) wort. Under pitching can lead to problems, but so can over pitching. For example, using very large yeast starters, and with this cell counts a factor 5 or more above the ideal, can lead to excessive sulfur levels. It can also create a variety of off flavors due to yeast autolysis. Synthetic fuels are produced using elevated pitching rates, but flavor is not an issue with these products! As with the other defects mentioned above, the best approach is to correct the original problem and not to rely on ageing.
5. Flavor Maturation
This in many respects is the most interesting part of lagering in the sense that the goal is not damage control, but rather taking a sound beer and improving it. Two mechanisms are fundamental. One concerns polyphenols. Extensive data shows that anaerobic cold storage favors the precipitation of phenols in the higher oxidation states. That is, cold anaerobic storage will reduce the beers redox potential. This promotes rounded flavors and a smooth palate for conventional lagering (0-2°C, 32-36°F), discernable improvements will be seen through 6-8 weeks. In the ice brewing process, the times are shorter as noted above.
The second effect is a slow esterification of fusel alcohols. The reduction of higher alcohols promotes a greater elegance of taste, even when these alcohols are below threshold. The esters so formed tend to be of the desirable type, and add to the beer's complexity. This effect is enzymatic, and depends on having viable yeast present in maturation to keep the beer "alive." Ideally, this should be between 500,000 and 750,000 cells per ml. This effect also depends on time. When Pilsner Urquell was fresh and brewed on a 3-6 month cycle, it displayed these effects to perfection.
6. Dry Hopping
As Greves noted in his paper, the addition of hops during cold maturation was a uniquely American practice. The most important historical examples showing the benefits of this procedure was (arguably) the Ballantine Ales, back in the days when Ballantine was an independent family owned brewery. Their flagship product was Ballantine XXX, which was dry hopped during a cold three month maturation period. This ale was noted for its full and attractive hop aroma, which was accompanied by a well defined but mellow hop bitter. Dry hopping will always achieve these effects, at least for a short period. The problem is that the aromatic compounds are unstable, and can quickly disappear. Ballantine XXX in its prime was a national beer, and subject to market abuse. Yet, typically around 5,000,000 bbls. were sold each year. The hop aroma was its signature, and hence the stability of it was a crucial point. The extended cold contact time played a fundamental role since it was during this period that the aroma compounds became bound up in the beer. Nugy8 suggests that one month of cold contact time with hops yields one month of stability for the aroma compounds. This is consistent with what has been reported about the Ballantine ales, and it is also consistent with my own brewing experiences.
The traditional carbonation of lagers takes place during cold storage. Beer is transferred from fermenters to maturation tanks with approximately 1% (by weight) of fermentable sugars present. The secondary fermentation which takes place creates sufficient CO2 to saturate beer. It has been my experience that 2.8-3.0 volumes of CO2 will be dissolved at equillibrium. Thus, it is desirable to take pressure and temperature readings so that adjustments can be made to desired levels. A 3 month cycle for this method is ideal if the beer is held under an appropriate counter pressure. I have found that 1 atmosphere (14.7 psi) is adequate.
I have personally not seen any difference in foam quality that can be attributed to the way beer is carbonated, either forced or natural. However, it has been my experience that people who are sensitive to carbonic acid, and dislike gassy beers, tend to prefer (by a wide margin) the flavor of the beers made with traditional carbonation when CO2 levels are in excess of 2.4 vols. The reasons for this are not altogether clear, but it could be that the traditional carbonation has CO2 more tightly bound up with other constituents.
To lager or not to lager is a question to which brewers will likely come to different answers. I recommend that brewers not blindly follow the rigid rules set up by others on this matter, but rather be guided by test brews. I have found the following to be useful.
(a) Do three batches of your everyday beer and lager for 3, 8, and 16 weeks, respectively.
(b) Do three batches of your favorite high gravity beer and lager for 3 weeks, 6 weeks, and 9 months respectively.
(c) Do two test batches, one being forced carbonated and the other carbonated by the traditional method.
It is of course desirable to control for extraneous effects. This is hard to do in a homebrewing content. However, the key items to control are yeast, brewing materials, and oxidation. In particular, the test brews should be staggered so that they can be bottled at the same time (or nearly so). If this is done, then it is my experience that what ever bias that may exist will not be significant enough to alter conclusions.
I realize that this program requires a lot of brewing, but then it also gives us an excuse to do more brewing, as if any of us needed such a reason!
 Arnold, J. P., Origin and History of Beer and Brewing, Wahl-Henius Institute, Chicago, 1911.
 Casey, G. P., Presentation at Rocky Mountain Microbrewing Symposium, Univ. of Colorado, Colorado Springs, Feb. 1999.
 One Hundred Years of Brewing, Arno Press, New York, 1974.
 A. Zimmermann, Brauereibe Briebslehre, Buffalo, New York, 1904.
 J. A. R. Greves, "On Some Recent Advances in Brewing in the United States," J. Institute of Brewing, Vol. III, 1897.
 G. J. Fix and L. A. Fix, "Analysis of Brewing Techniques,"
Br. Publ., 1997.
 G. J. Fix "Principles of Brewing Science," Br. Publ., to appear, October 1999.
 Nugy, Brewers Manual, Jersey Printing, 1948.
 G. J. Fix, Sulfur Flavors in Beer," Zymurgy, vol. 15, No. 3, 1992.
 Cahill, G., P. K. Walsh, D. Donnely, J. Am. Soc. Br. Chem., Vol. 57.2, 1999.
 George Lever, former Ballantine brewmaster, personal communication
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