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Studies supporting the use of mechanical mixing in large scale beer fermentations
journal contribution
posted on 2010-11-08, 16:55 authored by Alvin W. Nienow, Georgina McLeod, Christopher HewittBrewing fermentations have traditionally
been undertaken without the use of mechanical
agitation, with mixing being provided only by the
fluid motion induced by the CO2 evolved during the
batch process. This approach has largely been maintained
because of the belief in industry that rotating
agitators would damage the yeast. Recent studies have
questioned this view. At the bench scale, brewer’s
yeast is very robust and withstands intense mechanical
agitation under aerobic conditions without observable
damage as measured by flow cytometry and other
parameters. Much less intense mechanical agitation
also decreases batch fermentation time for anaerobic
beer production by about 25% compared to mixing by
CO2 evolution alone with a small change in the
concentration of the different flavour compounds.
These changes probably arise for two reasons. Firstly,
the agitation increases the relative velocity and the
area of contact between the cells and the wort, thereby
enhancing the rate of mass transfer to and from the
cells. Secondly, the agitation eliminates spatial variations
in both yeast concentration and temperature,
thus ensuring that the cells are maintained close to the
optimum temperature profile during the whole of the
fermentation time. These bench scale studies have
recently been supported by results at the commercial
scale from mixing by an impeller or by a rotary jet
head, giving more consistent production without
changes in final flavour. It is suggested that this
reluctance of the brewing industry to use (adequate)
mechanical agitation is another example where the
myth of shear damage has had a detrimental effect on
the optimal operation of commercial bioprocessing.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Chemical Engineering
Citation
NIENOW, A.W., McLEOD, G. and HEWITT, C.J., 2010. Studies supporting the use of mechanical mixing in large scale beer fermentations. Biotechnology Letters, 32 (5), pp. 623-633.Publisher
© Springer VerlagVersion
- AM (Accepted Manuscript)
Publication date
2010Notes
This article was published in the serial, Biotechnology Letters [© Springer]. The original publication is available at www.springerlink.com and the definitive version can be viewed at: http://dx.doi.org/10.1007/s10529-010-0213-0ISSN
0141-5492Language
- en