On food and cooking the science and lore of the kitchen ( PDFDrive ) 1407

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 small amount of yeast and some sugar or fresh wort, or some actively fermenting wort (this is called Kräusening) Inside the closed cask or tank, the liquid traps and absorbs the carbon dioxide produced Undesirable odors can be forced out of the beer by opening the container briefly and allowing some gas to escape These traditional techniques are sometimes replaced by simply pumping pure carbon dioxide into the beer — carbonating it Some hops or hop extract may also be added at this point to augment aroma, bitterness, or both A few days of cooling and the use of a “fining” agent — isinglass (fish gelatin), clay, and vegetable gums are common — precipitate suspended proteins and tannins that might later form a haze when the beer is chilled for drinking; this is called “cold stabilization.” The beer is then centrifuged to remove any remaining yeast and precipitate, filtered, packaged, and usually pasteurized  ... can be forced out of the beer by opening the container briefly and allowing some gas to escape These traditional techniques are sometimes replaced by simply pumping pure carbon dioxide into the beer — carbonating it... A few days of cooling and the use of a “fining” agent — isinglass (fish gelatin), clay, and vegetable gums are common — precipitate suspended proteins and tannins that might later form a haze when the beer is...small amount of yeast and some sugar or fresh wort, or some actively fermenting wort (this is called Kräusening) Inside the closed cask or tank, the liquid traps and absorbs the carbon dioxide produced