Brewer: Alec Moss, Half Moon Bay Brewing in Princeton-by-the-Sea, CA.
The big reason to lager your beer, the main benefit homebrewers are looking for, is to soften and mellow the flavor. Lagering adds a degree of maturity to the beer. It blends the flavors of the malt, hops and yeast. The cold temperature works as a natural environment in which this happens.
Lagering is not only for lager beers, such as the Pilseners or Oktoberfests of the world. Ales — in particular, strong ales such as barleywine — can benefit from being aged at cold temperatures over a long period of time. For ales, the lagering process is usually called conditioning. The process is the same, but different words are used to describe it.
These bigger ales need a longer time for their complex flavors to blend and mellow. Lighter beers don’t. In a light beer, you might want the hops to jump out at you, and in this case you might get away with a week or two of cold conditioning.
But say you make something like a barleywine. In barleywine, you have to add an enormous amount of hops to counterbalance all the malt that you used. Without sufficient conditioning, those hops will simply overwhelm the beer. Lagering, however, allows those hops to blend with the flavors of the malt. In the end, you can get a barleywine with incredible balance.
The correct temperature for lagering should be between 33–35° F (0.6-1.7° C). This temperature range is the same for lagers or ales.
Homebrewers will need a refrigerator or some other means to keep temperatures that low over a lengthy period of time. The minimum lagering period is one month. Otherwise, it really isn’t worth it. You need to give the beer time. Remember that, at cold temperatures, things happen more slowly because the yeast metabolism and chemical reactions are slowed. So, time becomes your ally.
During lagering, a small amount of additional fermentation occurs slowly. Also, oxygen that was introduced during racking into the lager vessel is eaten up by the additional fermentation. In case you were wondering, the cold temperature prevents autolyzation of the yeast that settles out in the lager vessel. Autolysis is the breakdown of all or part of the yeast by self-produced enzymes.
Commercial brewers will let their beer lager as long as they can, though economics may determine the need for a shorter lagering period. They recognize the benefits that lagering imparts on the final product. On a larger scale, I’d say the minimum lagering period is something like two weeks. Things happen slower, though, in smaller batches — the kind you have to deal with at home. Exactly why this is the case, I don’t really know. The bottom line is to aim for a minimum of one month when homebrewing.
Lagering is best achieved in bulk. You aren’t going to get the same results cold-storing your beer after it has been moved to the bottle. Typically, lagering is done with some yeast present, as this allows for additional fermentation and oxygen take-up. For homebrewers, this probably sounds exactly like bottle conditioning. But the fact is that beer doesn’t generally age well in the bottle (though it does better if there is a bit of yeast present). In fact, don’t make the mistake of thinking that aging bottle-conditioned beer is the same as lagering. It isn’t.