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Mechanical handling effects on brewers' yeast
Brewery fermentation involves the conversion of sugars to ethanol by yeast with the repeated reuse of the yeast to maximise the overall conversion of sugars to ethanol. Within this environment the yeast is subjected to mechanical handling which exposes the cells to shear stress. It is known that bio...
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| Format: | Thesis |
| Language: | English |
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Department of Chemical Engineering
2025
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| _version_ | 1867613309755195392 |
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| access_status_str | Open Access |
| author | Robinson, Andrew |
| author2 | Harrison, Sue |
| author_browse | Harrison, Sue Robinson, Andrew |
| author_facet | Harrison, Sue Robinson, Andrew |
| author_sort | Robinson, Andrew |
| collection | Thesis |
| description | Brewery fermentation involves the conversion of sugars to ethanol by yeast with the repeated reuse of the yeast to maximise the overall conversion of sugars to ethanol. Within this environment the yeast is subjected to mechanical handling which exposes the cells to shear stress. It is known that biological particles are sensitive to hydrodynamic stress and the resultant biological response may be observed by a decrease growth rate (Cherry and Papoutsakis, 1988), decreased viability, vitality and fermentation performance (Basson et aI., 1996), release of enzymes (Stathopoulos and Hellums, 1985), the release of fine particles from the cell wall (Lewis and Poerwantaro, 1991) and cell disruption (Engler and Robinson, 1981 ; Zhang et al., 1993). In particular with the handling of yeast, filtration difficulties have been reported as a result of excessive haze production caused by the action of centrifuges (Lim et al., 1992; Siebert et al., 1987). Mannan haze material has also been shown to result from the agitation of yeast slurries in baffled shake flasks (Lewis and Poerwantaro, 1991). The implications of yeast handling in the brewing industry are poor fermentation performance due to decreased yeast viability, foam instabilities caused by the release of protease and the formation of beer haze brought about by abrasion of the cell wall and cell lysis. It is generally accepted brewery practice to minimise the hydrodynamic stress to which the yeast is exposed (Boughton 1983, 1987; Ball, 1994). Few technical reports or rigorous experimental data are however available on the effect of hydrodynamic stress on the yeast in the brewing industry thereby indicating the need for this study. An analysis of the brewing flowsheet highlighted processes that have the potential to cause hydrodynamic stress damage to the yeast. These major processes include the transfer flow of yeast suspensions between the various stages in the yeast propagation plant as well as the pumping and flow of yeast slurries from a fermentation vessel, through a plate and frame heat exchanger to an agitated storage vessel. The separation of low concentrations of excess yeast between primary and secondary fermentations by centrifuges is a further shear environment to which yeast is exposed. Yeast handling occurs between the stages of a 'multiple batch propagation' and at the end of a fermentation when the yeast is in the late exponential growth or stationary phase respectively. The primary objective of this study was to assess the effect of hydrodynamic stress on brewers' yeast quality. Towards this aim, stationary phase yeast was exposed to hydrodynamic shear generated within a laboratory French Press following its aerobic and anaerobic growth. Within the brewery, the centrifugal separation of yeast and flow of yeast slurries through the cropping circuit were investigated with the aim of identifying critical operating conditions to minimise cell damage. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/42054 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:34:06.076Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Department of Chemical Engineering |
| publisherStr | Department of Chemical Engineering |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/42054 Mechanical handling effects on brewers' yeast Robinson, Andrew Harrison, Sue Chemical Engineering Brewery fermentation involves the conversion of sugars to ethanol by yeast with the repeated reuse of the yeast to maximise the overall conversion of sugars to ethanol. Within this environment the yeast is subjected to mechanical handling which exposes the cells to shear stress. It is known that biological particles are sensitive to hydrodynamic stress and the resultant biological response may be observed by a decrease growth rate (Cherry and Papoutsakis, 1988), decreased viability, vitality and fermentation performance (Basson et aI., 1996), release of enzymes (Stathopoulos and Hellums, 1985), the release of fine particles from the cell wall (Lewis and Poerwantaro, 1991) and cell disruption (Engler and Robinson, 1981 ; Zhang et al., 1993). In particular with the handling of yeast, filtration difficulties have been reported as a result of excessive haze production caused by the action of centrifuges (Lim et al., 1992; Siebert et al., 1987). Mannan haze material has also been shown to result from the agitation of yeast slurries in baffled shake flasks (Lewis and Poerwantaro, 1991). The implications of yeast handling in the brewing industry are poor fermentation performance due to decreased yeast viability, foam instabilities caused by the release of protease and the formation of beer haze brought about by abrasion of the cell wall and cell lysis. It is generally accepted brewery practice to minimise the hydrodynamic stress to which the yeast is exposed (Boughton 1983, 1987; Ball, 1994). Few technical reports or rigorous experimental data are however available on the effect of hydrodynamic stress on the yeast in the brewing industry thereby indicating the need for this study. An analysis of the brewing flowsheet highlighted processes that have the potential to cause hydrodynamic stress damage to the yeast. These major processes include the transfer flow of yeast suspensions between the various stages in the yeast propagation plant as well as the pumping and flow of yeast slurries from a fermentation vessel, through a plate and frame heat exchanger to an agitated storage vessel. The separation of low concentrations of excess yeast between primary and secondary fermentations by centrifuges is a further shear environment to which yeast is exposed. Yeast handling occurs between the stages of a 'multiple batch propagation' and at the end of a fermentation when the yeast is in the late exponential growth or stationary phase respectively. The primary objective of this study was to assess the effect of hydrodynamic stress on brewers' yeast quality. Towards this aim, stationary phase yeast was exposed to hydrodynamic shear generated within a laboratory French Press following its aerobic and anaerobic growth. Within the brewery, the centrifugal separation of yeast and flow of yeast slurries through the cropping circuit were investigated with the aim of identifying critical operating conditions to minimise cell damage. 2025-10-28T10:08:10Z 2025-10-28T10:08:10Z 2001 2024-08-13T13:56:30Z Thesis / Dissertation Doctoral PhD http://hdl.handle.net/11427/42054 eng application/pdf Department of Chemical Engineering Faculty of Engineering and the Built Environment University of Cape Town |
| spellingShingle | Chemical Engineering Robinson, Andrew Mechanical handling effects on brewers' yeast |
| thesis_degree_str | Doctoral |
| title | Mechanical handling effects on brewers' yeast |
| title_full | Mechanical handling effects on brewers' yeast |
| title_fullStr | Mechanical handling effects on brewers' yeast |
| title_full_unstemmed | Mechanical handling effects on brewers' yeast |
| title_short | Mechanical handling effects on brewers' yeast |
| title_sort | mechanical handling effects on brewers yeast |
| topic | Chemical Engineering |
| url | http://hdl.handle.net/11427/42054 |
| work_keys_str_mv | AT robinsonandrew mechanicalhandlingeffectsonbrewersyeast |