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Beer Fermentation
Fermentation Systems
Cylindroconical
This system is the most commonly used to produce both lagers and ales. As the name implies, the enclosed vessels are vertical cylinders with a conical base and, normally, a dished top, as shown in Figure 13.1. They range in size between 100 and 7,000 hl, have from a 1.5 to a 3: 1 ratio of height to diameter, and work under pressures of from 1 to 1.3 bars above atmospheric pressure. These fermenters (FVs) were originally intended to be dual-purpose, used for both fermentation and conditioning, but in practice they are mainly used for fermentation (60). These vessels are fitted with vacuum and pressure relief valves to compensate for rapid pressure changes when filling, emptying, or cycling cleaning solutions. Pressure and vacuum release mechanisms are needed to avoid explosion or implosion. For example, emptying such vessels without balancing pressure will lead to implosion, the most common cause of damage to tanks in craft breweries.
Many top-cropping yeast strains used in open fermenters will behave as bottom-cropping yeast strains in cylindroconical fermenters. This has allowed many British breweries to keep using their own "in- house" yeast strains with conical FV’s. In spite of their popularity, some traditional ale brewers still do not use cylindroconical fermenters to produce beer (60). This is because the carbon dioxide produced is in excess of that required in traditional ales. Nevertheless, traditional lager brewers have experienced few problems in using cylindroconical fermenters.
Traditional Ale Top System
This is the traditional ale skimming system used in the United Kingdom. It utilizes top-fermenting yeast cropped for repitching by skimming from the surface. The vessels are normally shallow and flat-bottomed and may be round, square, or rectangular. Traditionally, these vessels are open-topped to facilitate skimming and are located in a well-ventilated room to disperse the carbon dioxide evolved during fermentation. Some British brewers maintain that there is a smoother, rounded flavor produced with open fermentation tanks that is lost in tall cylindroconical tanks. Today many of the vessels are enclosed, allowing carbon dioxide collection, and the skimming is carried out by suction. The fermentation is controlled by attemperation using cooling panels on the walls of the vessel.
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