Chapter 10 - What is Different for Brewing Lager Beer?
10.2 Lower Temperatures
Lager comes from the German word "lagern" which means to store. A lager beer is in cold storage while it ages in the conditioning phase. Temperature influences lagers in two ways. During primary fermentation, the cooler temperature (45-55 °F) prevents the formation of fruity esters by the yeast. In addition to producing fewer byproducts during the primary phase, the yeast uses the long conditioning phase to finish off residual sugars and metabolize other compounds that may give rise to off-flavors and aromas. Unfortunately, this long time with the beer in contact with the yeast can be a problem. The problem is autolysis, i.e. yeast-suicide, which can produce terrible off-flavors in the beer.