Yeast and Fermentation Session
John P Carvell, Aber Instruments Aberystwyth UK
Co-author(s): Christopher Boulton, University of Nottingham, Nottingham, UK
ABSTRACT: The concept of using a radio-frequency impedance
(RFI) probe for measuring the concentration of live yeast cells was
first published back in 1987, and in this paper we review how this
invention has evolved over the last 20 years to become a critical
process control instrument in the modern brewery. The first biomass
sensor that detected cells, by virtue of their dielectric properties,
was designed for applications in bioreactors and could be used with a
wide range of eukaryotic and prokaryotic cells at relatively high cell
densities. In order to operate in breweries with packed yeast cell
densities at low and often varying conductivities, the original “biomass
monitor” instrument had to be substantially modified before the first
“yeast monitor” was introduced into the brewing market in 1991. The
justification for installing a yeast monitor is usually based on the
ability of the probe to provide precise and repeatable control of yeast
pitching rates. It follows that procedures that lead to precise and
repeatable control of yeast pitching rate will result in consistent
fermentation performance. The traditional methods of taking a grab
sample from the yeast storage vessel, diluting, and then quantifying the
live yeast concentration in the laboratory are time-consuming and
require skilled personnel to ensure precision and repeatability. Most of
the large international brewing groups have now installed the Aber
yeast monitor, and in recent years some of the larger microbreweries are
now operating with the system. The actual improvements to a process
after installation of the instrument were first published by the Bass
Brewing Group, Miller, and Guinness in the early 1990s, but much of the
data in this area are still not public. A comprehensive study by SAB
Miller in 2011 shows the improvements in fermentation rates and the real
degree of fermentation for certain brands after the installation of the
yeast monitor. Although the vast majority of applications of RFI in the
brewing industry are in-line applications with the probes installed
around the yeast storage vessels, the probe is being used to monitor and
in some cases control the fermentation process. The most comprehensive
study with brewing fermentors involved following the spatial
distribution of live yeast within a production vessel using a series of
submergible RFI probes. We also show how the probe has become a critical
control parameter for some continuous fermentation in bioethanol and
other non-brewing fermentations. This review of the development of the
yeast monitor for the brewing process concludes with the introduction of
a compact version of the instrument where the electrodes and the
electronics are all built into an IP 65 stainless steel housing. We
describe the rationale behind the new design and show how the same
components can be utilized within an off-line instrument and a version
for mounting on propagators and fermentors.
John Carvell is a
graduate in biochemistry and received his Ph.D. degree at Newcastle
University, U.K. He held roles as production manager at yeast
manufacturer and senior sale roles within APV and Alfa Laval before
joining Aber Instruments Ltd. as a director. With the business over 90%
export and split between both the brewing and biotechnology industries,
he spends a large proportion of his time visiting key customers involved
in a diverse range of applications. John has presented posters at many
of the major brewing conferences and also presented papers at the SIM
(Society of Industrial Biotechnology), RAFT (Recent Advances in
Fermentation Technology), ACS, ASBC, and MBAA annual meetings. When time
permits John enjoys a number of activities, including badminton and fly
fishing, as well as coaching a junior cricket team.
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