bottom-fermented beer is somewhat different.
The original Bavarian lager was packed in ice
and allowed to rest in contact with its yeast
dregs for several months. The yeast slowly
produced carbon dioxide, which helped purge
the beer of sulfury off-odors. Today, some
traditional lagers are still aged for several
months; but because storage has the economic
disadvantage of tying up money and
materials, the tendency is to lager the green
beer at temperatures just above freezing for
two to three weeks. Carbon dioxide may be
pumped in to purge undesired aromas; and
centrifuges, filters, and additives help clarify
the beer. As a replacement for wooden casks,
some beech or hazelwood chips may be
thrown into the tank for flavor.
Additives More than 50 additives are
permitted in American beer, including
preservatives, foaming agents (usually
vegetable gums), and enzymes — similar to