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.
