Continuous Fermentation is a method of converting wort into beer in a continuous process, whereby wort is fed into one end of the process and beer is discharged at the other without recourse to holding the beer in a static holding vessel (batch fermentation). The advantages claimed for continuous methods include efficient plant utilization, improved carbohydrate utilization, increased throughput, and consistency. However, microbial contamination, flavor differences with batch fermented beers, and the requirement for continuous processes upstream and downstream from fermentation, particularly in wort production, are major disadvantages this method. Additionally, continuous fermentation is somewhat inflexible in that it does not allow the brewer to respond to fluctuations in demand. In situations where a standard base beer is required before secondary adjustments for different strengths, colors, and flavors, the method has been found viable. Various methods of continuous fermentation have been attempted over the past 100 years or so but with limited success. By far the most successful is the so-called Coutts system which has operated in New Zealand for over 30 years. Beer and recycled yeast are mixed with aerated wort and, after yeast growth occurs, the fermenting beer is passed to succeeding vessels in a cascade system. The total residence time in the fermentation system is about 30 hours. An alternative approach using a single vessel only was pioneered by the British brewer Bass in the 1970s. Known as the “tower continuous fermenter,” this method generated a fermentation gradient within a single tank within which a body of yeast was retained within the tower, enabling rapid fermentation rates. However, it was prone to microbial infection and “blow-outs”—loss of the yeast that was effectively washed out of the fermenter. The principle of retaining a mass of yeast within a tower was developed by applying the process of immobilization of the yeast within the fermenter. In this method, the brewing yeast is immobilized on woodchips in a one-stage reactor, thus preventing possible blow-out. This method has been used to brew both stouts and lager beers in Finland, with production times of 20–30 hours and consistent flavor development.
