As soon as the liquid becomes still the yeast cells and other solid matters begin to separate. Those that are lighter come to the top and those which are heavier, which is the greater number, sink to the bottom of the vessel. When the separation is practically finished the beer may be drawn oft" into storage tanks, or, in order to insure greater limpidity, may be filtered into the storage tanks. These tanks are kept at a low temperature, usually in cellars, where the completion of the secondary fermentations and the ripening of the beer go on. When beer is stored for improving its quality in this way the finished product is known as "lager." The best beers are those which are ripened in this way for a period of from 9 to 12 months. Usually the period of storage is much less. Beers are often sold in from three to four weeks after manufacture, but these are more or less raw in character and not to be compared in quality with those stored for a longer time.