The Brewing Process
Readings: Bamforth pp. 25-43, 53-58
The Brewing Process
Karl J. Siebert
Introduction
Like wine, beer contains many chemicals that collectively result in its sensory properties: color, flavor, haze and foam. Like wine making, brewing is a batch process, although breweries operate continuously through the year. Beer can be made with only barley malt, hops, yeast and water, as it still is in most of Germany and is the case with most microbreweries. However, major brewers in most other countries use an additional source of starch or sugar called an adjunct.
Unlike the case in wine, where pressing a grape results in a fermentable substrate, the nutrients in the brewing raw materials are in a form that yeast is unable to utilize. The conversion of starch to simple sugars and proteins to amino acids occurs in the brewhouse. Fermentation of the resulting mixture, called wort, then occurs. Finally the freshly fermented beer is subjected to storage (in the case of a bottom-fermented, or lager, beer this is called lagering) to mature flavor and colloidal stability. After finishing (usually some stabilization treatment followed by filtration) the beer is packaged.
Brewhouse
A large number of mechanical and thermal operations are performed in the brewhouse in order to prepare a fermentable substrate for yeast and to extract flavor and color principles from malt and bitter principles and aroma from hops. Malt and cereal adjuncts are first milled to provide easy access of water to the interior. If a starchy adjunct is used, water is added to it and a small portion of the malt in the adjunct cooker and the mixture is heated rapidly to boiling. The malt enzymes partially digest the adjunct starch to render it less viscous. The remaining malt is mixed with water in the mash vessel and subjected to a temperature program to facilitate the action of malt enzymes that convert starch into sugars and protein into amino acids. During the mashing process the contents of the adjunct cooker are pumped into the main mash and cause one of the temperature rises. Separation of the insoluble matter takes place in a filtration vessel, most often a lauter tun, where the malt husks serve as the filter medium. The wort is transferred to the kettle where it is heated to boiling and then boiled for about 90 min. Toward the end of the boil hops are added and the bitter compounds are formed. Some hop aroma compounds are also extracted. Boiled wort is transferred to a hot wort tank, where heat coagulated material is separated from the wort, which is then cooled and aerated.
Fermentation
Culture yeast is added to the cooled, aerated wort and fermentation begins. The fermentation produces alcohol, CO2, and a range of other flavor compounds in lesser amounts. At the end of fermentation the yeast flocculates and either rises to the top of the fermenter (top fermenting or ale yeast) or sinks to the bottom (bottom fermenting or lager yeast). Most of the yeast is removed from the fermenter and reused in subsequent brews. The resulting beer is transferred to the storage tank.
Maturation
The freshly fermented beer resides in the storage tank at temperatures slightly above freezing. This allows time to achieve flavor and colloidal maturation. For a lager this generally takes between 10 days and several weeks. For an ale this can be as short as three days.
Finishing
After maturation the beer is filtered, subjected to colloidal and microbiological stabilization treatments, and packaged in bottles, cans, kegs or casks.