Perfect yeast management is one of the key starting points for improving beer quality. Yeast management must occur at a uniform level to ensure consistent beer quality.
A yeast propagation system helps achieving two key objectives. First, the propagation of the yeast only, foreign yeast and bacteria are not reproduced to any significant extent. Second, creating a vital, healthy and fermentable yeast.
The vitality of the yeast is reduced during normal brewery operation and during repeated yeast pitching. The yeast is subject to pressures, pressure changes, shear forces, unsuitable temperatures, temperature changes, and osmotic stresses (differences in concentration) due to water or beers with too high alcohol content for the yeast. Reduced yeast vitality will extend beer processing times and negatively impact on beer flavour.
30% freshly propagated yeast is added for each pitch in the fermentation tank if a yeast propagation system is used. The industrial yeast in the brewery is thus always kept clean and it maintains its vitality. This ratio ensures that beer with a consistent taste is produced. Customers are after all perfectly able to detect differences in taste. The smoothness of a beer is a sign of high quality.
AMS YEAP - Single tank yeast propagation.
The tank is operated with a minimum overpressure as pressure is a stress factor for the yeast organism. Pressure-free operation requires sufficient unfilled tank space. After tank and system are CIP cleaned, the tank is filled with sterile wort up to approximately 20% of the liquid volume (not the tank volume). The wort is cooled down to propagation temperature (14-20°C) and ventilated with sterile air. Ventilation occurs in a transfer line. Finally, the yeast is passed from a Carlsberg flask into the propagation tank or the transfer line via a sampling valve.
AMS YEAP - Yeast propagation process.
The control provides the necessary lead time for the yeast with the propagation programme. The process time is dependent on the yeast quantity supplied. The propagation programme consists of a temperature programme, a circulation programme and a ventilation programme. The propagation continues until the desired residual extract, required as the yeast will change undesirably without the appropriate nutrients (mutation). Then the tank is filled to 100% of the liquid volume (approximately 55% of the tank volume) and the yeast propagation procedure is repeated in the same way.
AMS YEAP - Yeast pitching, recovery & CIP.
Finally, approximately 80% of the fill volume is removed from the propagation tank and used for "pitching" of the fermentation tanks. The remaining 20% of the fill volume is filled back up to 100% of the fill volume (55% of tank volume) with tempered sterile wort to act as a starter culture. No addition of yeast from the Carlsberg flask is required in this case. This process can, however, not be repeated indefinitely as the tank and the system must undergo thorough CIP cleaning following several yeast cycles. The yeast propagation process starts all over again after each CIP cleaning cycle, which means that fresh, vital yeast is always obtained