High gravity primary continuous beer fermentation using flocculent yeast biomass

Abstract

The current work assessed a new immobilized cell reactor system throughout a long-term (54 days) continuous primary fermentation of lager-type wort of high specific gravity. The experiment was performed in a 4 L airlift bioreactor and immobilization of biomass was attained solely by flocculation. Despite the constant liquid agitation and washout of biomass, up to 53 g dry wt/L of yeast remained immobilized in the system. Two types of beer were produced without interrupting the reactor, based on two types of wort: a Pilsener type with high specific gravity of 15.6 ± 0.3°P; and a dark lager wort with specific gravity of 14.4 ± 0.03°P. Even during the inlet of high gravity wort, the desired attenuation was achieved without the need for either recirculation or an auxiliary second stage bioreactor. The specific saccharide consumption rate was kept around 7.9 ± 0.4 g/L/h and ethanol productivity oscillated at 3.36 ± 0.2 g/L/h for nearly a month. During this period the volumetric productivity of the current bioreactor reached 1.6 L beer/L/day. The green beers produced from the Pilsener and dark lager worts met the standards of regular finished primary beer fermentation. The productivity of diacetyl through the entire experiment could be correlated to the free amino nitrogen consumption rate.

Continuous beer fermentation - diacetyl as a villain

“…However, as Table shows, biomass accumulation by flocculation presented an increasing trend throughout the experiment and was unaffected by altering process conditions. This tendency was also observed in a previous experiment . Traditional batch fermentations on the other hand use around 10–20 × 10 6 cells mL −1 as an initial pitching rate, which reaches nearly 70 × 10 6 cells mL −1 after exponential growth.…”

“…As in these batch experiments, the only real problem observed in the current work that required closer attention was the diacetyl levels. Yet there is evidence that the problem does not necessarily relate to the amount of immobilized yeast, as further discussed.…”

“…If there is a key parameter affecting continuous beer production, it is the FAN consumption rate (FCR) . The environment provided by the current setup (strong agitation, oxygen and high organic loading rate) was very favourable for increased yeast metabolism.…”

“…However, after a few days and without the interference of diacetyl, P2 presented a very pleasant (flower-predominant) aroma and a good taste. If there is a key parameter affecting continuous beer production, it is the FAN consumption rate (FCR) (22). The environment provided by the current setup (strong agitation, oxygen and high organic loading rate) was very favourable for increased yeast metabolism.…”

“…This condition results in a deficient FAN consumption and also imparts an unbalanced flavour profile to the finished beer (4). Recent findings have shown the crucial role of FAN consumption rate in diacetyl formation (15,16,22).…”