The Operating System
Fermentation and lagering are a simple matter of regulation and monitoring. Set your regulator to 50-52 degrees for primary fermentation. Lager yeasts produce sulfur compounds during fermentation, but they will dissipate with proper lagering. Primary should last about seven to 10 days for lower-gravity wort to as long as three or four weeks for higher-gravity ones. The end point of primary signals the time to begin the diacetyl rest, so steal a sample to taste and take a gravity reading to ensure completion. If it is lagging, you can let it sit for a few more days, which won’t have any adverse effects, or raise the temperature a couple of degrees.
Once primary fermentation has finished, perform a diacetyl rest by raising the temperature to 57-60 degrees for one to two days. There may be some outgassing or minor fermentation, but it is important to proceed to cooling after no more than two days. Prepare the wort for lagering by dropping the temp to 40 degrees gradually over a few days to drop the yeast. When the wort is fairly clear, rack to your lagering vessel, carboy or corny keg, and take the temperature to 32-35 degrees over a few days. Leave as little air space as possible in the lagering container. This is where the magic of lagering takes place, slowly metabolizing spent yeast remnants and consuming nasty metabolites, scrubbing the wort clean. Lagering also precipitates soluble proteins, effectively clarifying the beer. Lagering times will vary from three weeks for lower-gravity brews to eight weeks or more for strong ones. Once finished, the beer can be kegged, carbonated and consumed as usual. If you bottle, dose the beer with some fresh lager yeast (one propagator smack pack, part of a pitchable tube or half a pack of dried lager yeast) and your priming solution and bottle-condition for a few weeks at 45 to 55 degrees.