ten days, and produces a milder flavor.
Bottom fermentation is the standard technique
in the United States. Because warm
temperatures encourage yeasts to generate
particular aroma compounds (esters, volatile
phenols), top fermentation produces fruity,
spicy aromas; cold, slow fermentation
produces crisp beers with a dry, bready flavor.
Conditioning The treatment of beer after
fermentation varies according to the type of
fermentation that has taken place: brief for
fast top fermentation, prolonged for slow
bottom fermentation.
Top-fermented beer is cleared of yeast and
then run into a tank or cask for conditioning.
The green beer, as it’s called fresh from
fermentation, contains little carbon dioxide,
has a sulfurous, harsh flavor, and is hazy with
the detritus of dead yeast cells. In
conditioning, a secondary fermentation is
induced by adding to the green beer either a