Characteristics of High Cell Density Fermentations with Different Lager Yeast Strains

Pieter J. Verbelen^1,2, Sebastiaan Van Mulders¹, Daan Saison¹, Stijn Van Laere¹, Filip Delvaux¹ and Freddy R. Delvaux¹
¹ Centre for Malting and Brewing Science, Faculty of Bioscience Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, box 2463, 3001 Heverlee, Belgium
² Corresponding author. E-mail: Pieter.Verbelen@biw.kuleuven.be

J. Inst. Brew. 114(2), 127–133, 2008 | VIEW ARTICLE

ABSTRACT
To improve the productivity of the beer fermentation process, several strategies can be adopted. One of these promising strategiescould be the increase of suspended yeast cells in the reactor. Therefore, the fermentation characteristics of 11 lager yeast strains were studied in normal pitched worts (20 × 10⁶ cells/ mL) (LD) and in worts with a four-fold higher pitching rate (HD). The fermentation rate was 2-4 times increased when high initial cell levels were used. The net yeast growth was somewhat similar between the LD and the HD fermentations, although the FAN uptake level was about 35% higher in the HD fermentations compared with LD. High viabilities were observed throughout the fermentations with high cell loadings. HD fermentations resulted in higher concentrations of all the measured fusel lcohols and higher maxima and residual concentrations of total diacetyl were observed. In contrast, higher levels of most of the esters were found at the normal pitching rate, although the results of isoamyl acetate were not significant. With the help of “Principal Component Analysis”, it became clear that the cell density had an important influence on the flavour profile, but that yeast specific preferences could not be overlooked as they determined the sensitivity of the yeast to the application of higher cell densities.

Key words:
Fermentation, flavour compounds, high gravity brewing, pitching rate, Saccharomyces cerevisiae, yeast metabolism.