Lager yeast is a bottom fermenting yeast (meaning it is most active near the bottom of the fermenting beer) that ferments at colder temperatures, generally between 32 and 55 degrees F (0-13 degrees C). Lager yeasts tend to be neutral in flavor and aroma and thus do not produce the fruity esters found in ale yeasts. Beers fermented with lager yeasts are usually cold stored at temperatures below 45 degrees F (7 degrees C) following primary fermentation for a period of a few weeks to several months-a process known as lagering.