| MBAA TQ http://dx.doi.org/10.1094/TQ-54-1-0215-01 |
Optimization of Beer Fermentation with a Novel Brewing Strain Torulaspora
delbrueckii Using Response Surface Methodology
Maximilian Michel, Tim Meier-Dörnberg, Fritz Jacob, Hubertus Schneiderbanger,
Korbinian Haselbeck, Martin Zarnkow, and Mathias Hutzler. Research Center
Weihenstephan for Beer and Food Quality, Technische Universität München, Alte
Akademie 3, 85354 Freising, Germany.
The use of novel brewing strains coming from the non-Saccharomyces
sector adds new challenges but also new desirable aromas to beer. Some research
teams have focused on screening new yeast species from biodiversity for their
fermentation potential. The next step in creating novel brewing strains is the
optimization of the fermentation process for the actual production of beer. Here
a response surface methodology was used to adjust the fermentation process with
a strain (T9, Torulaspora delbrueckii) found for potential use in a
previous study. An oxygenation rate test was performed to investigate the
oxygen requirement of the strain. Also, an evaluation of volatile flavor
compounds and final flavor judgment by trained panelists were undertaken. The
fermentation conditions were chosen according to prior testing at varying
fermentation temperatures between 15 and 25°C and pitching rates due to
relatively small cell sizes of between 50 × 106 and 120 × 106 cells/mL.
Further, the optimal time of pitching from propagation in connection with
viability, vitality, and cell count was investigated. The wort used was diluted
to 12.5°P from wort extract for standardized conditions. Wort oxygenation until
10 mg/L of dissolved oxygen was found to be sufficient. Propagation cell counts
reached up to 400 × 106 cells/mL in 28 h before viability decreased.
Fermentation at 20°C and a pitching rate of 60 × 106 cells/mL led to the most
desirable beer with a blackcurrant and honey-like flavor. A shift of flavor was
found from honey-like at low temperatures to wine-like at higher temperatures.
Keywords: Torulaspora delbrueckii, Alternative yeast,
Nonconventional yeast, Beer