Continuous tower fermentation - experiences in establishing large scale commercial production.
The plant consists of four towers (25 x 3.5 ft) and one (25 x 6 ft) run in parallel to give a weekly output of 12,000 brl. Wort is stored hot, centrifuged to remove trub and hop powders, passed through plate sterilizers (95 degrees C), cooled to 16 degrees C and metered into the base of the towers. Sterile air and carbon dioxide (for control of yeast plug porosity) are fed into the wort line at the base of the towers. The yeast chosen was flocculent, but did not compact into a nonporous plug; it produced flavour matching that of the conventional beer, with low reproductive capacity. Fermentation was controlled at 18 degrees C by jacket cooling. Flow rates are increased only in small increments so that outlet gravities do not rise by more than 0.25 to 0.50 degrees Plato and time to reestablish steady conditions is allowed. Best product consistency was achieved at high flow rates consistent with stable physical conditions of the plug and stable effluent gravity. Satisfactory ale can be produced with a residence time of 4 h in the towers. Effluent beer passes to a green beer centrifuge, thence to conditioning tanks, where it is cooled to -1 degrees C in 12 h and conditioned for 4 days before filtration, flash pasteurization and kegging. The routine of operation, including the maintenance of sterility, chemical, microbiological and organoleptic quality control, flavour matching and future developments (including lager production), are discussed. The financial viability of tower operation depends on high throughputs of a single product. Compared with a batch installation there is an increased capital cost (about 50% and 10% for untts producing respectively 6,000 and 23,000 brl per week), but there is a reduction in working capital, because of smaller volumes of fermenting and conditioning stock and there are significant operational gains and savings in labour and cleaning. Continuous stable operation for more than 6 months has been achieved and warm conditioning for flavour development has been eliminated.
Keywords: beer brewing continuous process equipment fermentation maturation tank