APPLIED MICROBIAL AND CELL PHYSIOLOGY
Impact of pitching rate on yeast fermentation performance
and beer flavour
P. J. Verbelen
&
T. M. L. Dekoninck
&
S. M. G. Saerens
&
S. E. Van Mulders
&
J. M. Thevelein
&
F. R. Delvaux
Received: 28 August 2008 / Revised: 28 October 2008 / Accepted: 29 October 2008 / Published online: 19 November 2008
#
Springer-Verlag 2008
Abstract The volumetric productivity of the beer fermen-
tation process can be increased by using a higher pitching
rate (i.e. higher inoculum size). However, the impact of the
pitching rate on crucial fermentation and beer quality
parameters has never been assessed systematically. In this
study, five pitching rates were applied to lab-scale
fermentations to investigate its impact on the yeast
physiology and beer quality. The fermentation rate in-
creased significantly and the net yeast growth was lowered
with increasing pitching rate, without affecting significantly
the viability and the vitality of the yeast population. The
build-up of unsaturated fatty acids in the initial phase of
the fermentation was repressed when higher yeast
concentrations were pitched. The expression levels of
the genes HSP104 and HSP12 and the concentration of
trehalose were higher with increased pitching rates, sug-
gesting a moderate exposure to stress in case of higher cell
concentrations. The influence of pitching rate on aroma
compound production was rather limited, with the excep-
tion of total diacetyl levels, which strongly increased with
the pitching rate. These results demonstrate that most
aspects of the yeast physiology and flavour balance are
not significantly or negatively affected when the pitching
rate is changed. However, further research is needed to fully
optimise the conditions for brewing beer with high cell
density populations.
Keywords Fermentation
.
Brewer’s yeast
.
Yeast
metabolism
.
Yeast physiology
.
Stress response
.
Flavour
Introduction
In the traditional production of lager beer, the fermentation
process is the most time-consuming step, which takes about
1–2 weeks before entering the maturation period. There-
fore, an important objective of modern fermentation science
and technology is to reduce the fermentation time while
producing an end product of similar quality and thus
allowing great time and money savings. To improve the
volumetric productivity of the beer fermentation process,
several strategies can be adopted. For example, a major
approach was the application of continuous fermentation
with immobilised yeast, allowing a large increase in cell
density, which resulted in faster fermentation rates. The
interest in using immobilised yeast for primary beer
fermentation seems to have dropped because of persistent
engineering problems, unbalanced beer flavour and unreal-
ised cost advantages (Brányik et al. 2005). However, the
main aim of the technology was to improve the productivity
by maximising the cell concentration in the reactor.
Therefore, another promising strategy may be to enhance
the amount of suspended yeast cells in a batch fermentor
(i.e. ‘the pitching rate’; Okabe et al. 1992; Verbelen et al.
2008). However, an increase in the pitching rate could also
have deleterious side effects on the physiological condition
Appl Microbiol Biotechnol (2009) 82:155–167
DOI 10.1007/s00253-008-1779-5
P. J. Verbelen (*)
:
T. M. L. Dekoninck
:
S. M. G. Saerens
:
S. E. Van Mulders
:
F. R. Delvaux
Centre for Malting and Brewing Science,
Faculty of Bioscience Engineering,
Katholieke Universiteit Leuven,
Kasteelpark Arenberg 22, P.O. Box 2463, 3001 Heverlee,
Belgium
e-mail: Pieter.Verbelen@biw.kuleuven.be
S. M. G. Saerens
:
J. M. Thevelein
The Laboratory of Molecular Cell Biology,
Department of Molecular Microbiology (VIB),
Institute of Botany and Microbiology,
Katholieke Universiteit Leuven,
Kasteelpark Arenberg 31,
3001 Heverlee, Belgium