The Combined Effects of Oxygen Supply Strategy, Inoculum Size and Temperature Profile on Very-High-Gravity Beer Fermentation by Saccharomyces cerevisiae

Abstract

The timing and concentration of oxygen supply to wort are of particular relevance in industrial beer brewing where tank volumes exceed brewhouse capacity, thereby necessitating fermenter filling in a multiple-brew fashion. A simple technique for accurately controlling dissolved oxygen concentration is presented to model industrial, multi-brew fermentations at bench and pilot scales. This method was employed to identify an effective oxygen supply strategy for batch fermentations conducted with very-high-gravity (VHG) wort. Addition of 25 ppm dissolved oxygen to the fermenting wort, 12 h after inoculation, was the most effective oxygenation strategy and reduced fermentation time by 33% compared to the control conditions. Pilotscale trials were subsequently conducted to further optimize VHG batch fermentation performance through simultaneous manipulation of key fermentation process parameters, including increased yeast inoculum size, early and increased free-rise timing and temperature, and optimized oxygenation strategy. This approach reduced the time to achieve end of fermentation targets by 34% compared to trials conducted under control conditions. The improved fermentation profile was consistent over three successive inoculations and minimal impact was observed on key flavour volatiles. Employing the optimized process for VHG batch beer production would be industrially desirable due to the potential for improved process efficiency and cost-savings.

Optimisation of fermentation conditions for bioethanol production from oil palm trunk sap by Saccharomyces cerevisiae

“…As excessive inoculum in the medium compromises fermentation rate, ethanol production and recovery (Jones et al, 2007), a suitable and optimal inoculums size is critical to achieve more efficient bioethanol production from OPT sap. Figure 4 shows bioethanol production profile from OPT sap at different initial inoculum size.…”

Stress responses in brewing yeast.

“…Přechod z aerobní fáze růstu (propagace) do anaerobní (fermentace) a opačný přechod se u spodních kvasinek projevuje výraznými změnami v růstové rychlosti nebo rychlosti produkce ethanolu [24,25]. Při přechodu z anaerobního růstu k aerobiose se rychle zvyšuje specifická aktivita CuZn-SOD, při opačné tranzici se její aktivita snižuje.…”

“…Data on the physiological effects of the transition from aerobic propagation to anaerobic fermentation and the reverse transition (from anaerobiosis to aerobiosis) on bottom-fermenting brewing yeast [24,25] showed that neither type of transition led to significant changes in growth rate or the rate of ethanol production. A rapid increase in the specific activity of CuZn-superoxide dismutase occurred on transition from anaerobiosis to aerobiosis, and a decrease in activity on the reverse transition, while catalase activity remained unchanged by the transitions.…”

“…Toxický účinek kyslíku je způsoben hlavně superoxidem a reaktivními formami kyslíku odvozenými ze superoxidu. Hlavní ochrannou funkci proti ROS zastává Cu,Zn-SOD [24,25], zatímco Mn-izoenzym této superoxiddismutasy ochraňuje buňku i proti vysoké osmolaritě a teplotnímu stresu a stresu vyvolaném metaloidy [47]. Syntéza Cu, Zn-enzymu de novo není vždy tak rychlá, aby zajistila plnou ochranu buňky.…”

“…The toxic effect of oxygen was found to be due to superoxide (or ROS species derived from it). The chief protective role against ROS is played by Cu,Zn-superoxide dismutase [24,25]. while the Mn-isoenzyme also plays a role in protecting the cells against high osmolarity, heat and metalloid stress [47].…”