Commercial Lagering.
Beer is transferred to a separate tank for maturation in traditional lagering methods.
Before the end of primary fermentation cooling is applied to the cone of the fermenter to
achieve a temperature of 5 C (41 F). The remainder of the beer above the cone (at least
95% of the volume) is at a higher temperature to ensure effective diacetyl removal.
Cooling below 5 C (41 F) is not necessary and runs the risk of cooling the beer beyond
its point of maximum density when inversion of flow around the fermenter may occur
(Andrews, 1997). About 24 hours after applying cooling an initial removal of yeast is
usually carried out. This yeast is usually discarded. When diacetyl reduction is complete
the remainder of the beer is slowly cooled to 5 C (41 F) to complete the maturation by
adjusting the flavour volatiles. A sudden fall in temperature must be avoided or the shock
may induce the yeast to excrete protease enzymes that could be detrimental to foam
stability. This cooling may take from two to nine days. At the end of this period a second
removal of yeast is usually made. The beer is now completely cooled to at least -1C
(30 F). The period of colloidal stabilization now takes place at -1 to -2 C (30 to 28F)
for two to three days. A final yeast removal is made before filtration. The colloidal
stabilization temperature must be maintained throughout the whole vessel.
There are many variations on this technique which would still be regarded as
traditional. Indeed the times can be much longer (Miedaner, 1978) with storage times at
-1 C (30F) being up to six weeks. In this situation up to 40% of the capital cost of the
brewery could be in the tanks required to condition beer (Coors, 1977). Fermentation and
maturation can also be carried out in one vessel so avoiding transfer between primary and
secondary fermentation.
Because of the high capital costs associated with building tanks and the working
capital of stored beer, brewers have sought to reduce maturation times. Yeasts with the
ability to reduce diacetyl rapidly have been used and warm storage times have been
almost eliminated. There are almost as many variations on maturation technique as there
are breweries. At least one successful system comprises: fermenter filling 20 hours,
primary fermentation 72 hours, warm storage 48 hours, cooling 48 hours, cold storage at
-1 C (30 F) 36 to 48 hours. Total time is less than ten days. These systems can produce
sound beer. However things can go wrong and they are susceptible to variations in raw
material quality. To escape from periods of uncertainty over maturation and hence
flavour stability, brewers need to keep in mind the traditional principles of the process.
