Slides
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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.
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FS430:
Understanding Wine and Beer