Publicação
Reduction of startup time and maintenance periods in continuous beer fermentation using immobilized yeast onto brewer's spent grains
| Resumo: | The current project aimed at solving technical problems involved on the implementation of a bioreactor (airlift) for continuous primary beer fermentation. In order to operate in continuous mode, the reactor must be capable of retaining a large amount of immobilized biomass. The first strategy taken towards this achievement was to effectively obtain a yeast carrier from Brewer´s Spent Grains (BSG) by suggesting several different chemical treatments. The ideal yeast carrier was obtained from a 40 min caustic treatment and had about 56% of cellulose content. This material was then used for yeast immobilization in two continuous beer fermentations. In these fermentations, foam fractionation was suggested as a method for continuous skimming non-viable biomass out from the bioreactor. The suggested setup presented good performance (rs = 2.95-3.62 g.L-1.h-1; and rp = 1.33-1.73 g.L-1.h-1) on continuous beer fermentation and a viability difference between yeast subpopulations from foam and remaining yeast in the reactor has been observed suggesting the feasibility of foam fractionation for dead biomass skimming. Yet, it has also been observed that flocculated biomass surrounding the biocatalysts were contributing in a large extent for the total immobilized biomass in the reactor. Thus, an assay testing the feasibility of flocculation as sole way of biomass immobilization in an airlift reactor was carried out. This new and simpler setup has shown much better performance than carriers’ based setups for biomass loading capacity (25 gcell dry wt..L-1), presenting very similar fermentation rates (rs = 3.4 g.L-1.h-1; and rp = 1.54 g.L-1.h-1). Then, two other continuous primary beer fermentations were carried out in order to test the feasibility and quality of beer produced using similar flocculation-based setups. In the first and longer fermentation up to 52 gcell dry wt..L-1 were attained through flocculation. Fermentation rates were higher than any other setup suggested by the literature for continuous beer fermentation (rs = 8.7 g.L-1.h-1; and rp = 3.7 g.L-1.h-1). This experiment was also very relevant as it was possible to correlate many other variables (such as FAN consumption rate influencing higher alcohols and diacetyl formation) contributing for the success of the suggested system. The last experiment was carried out at the laboratories of a large commercial brewery where some important parameters could be better controlled (fast feedback of results by automated beer analyzer, fresh wort always available, etc.). The results were consistent with the ones observed in the last mentioned experiment, replicating its outstanding performance (rs = 9.43 g.L-1.h-1; and rp = 3.75 g.L-1.h-1). Moreover, the beer from flocculated based setup was of excellent quality, confirmed by a professional panel of beer specialists. |
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| Autores principais: | Pires, Eduardo J. |
| Assunto: | Engenharia e Tecnologia::Engenharia Química |
| Ano: | 2014 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The current project aimed at solving technical problems involved on the implementation of a bioreactor (airlift) for continuous primary beer fermentation. In order to operate in continuous mode, the reactor must be capable of retaining a large amount of immobilized biomass. The first strategy taken towards this achievement was to effectively obtain a yeast carrier from Brewer´s Spent Grains (BSG) by suggesting several different chemical treatments. The ideal yeast carrier was obtained from a 40 min caustic treatment and had about 56% of cellulose content. This material was then used for yeast immobilization in two continuous beer fermentations. In these fermentations, foam fractionation was suggested as a method for continuous skimming non-viable biomass out from the bioreactor. The suggested setup presented good performance (rs = 2.95-3.62 g.L-1.h-1; and rp = 1.33-1.73 g.L-1.h-1) on continuous beer fermentation and a viability difference between yeast subpopulations from foam and remaining yeast in the reactor has been observed suggesting the feasibility of foam fractionation for dead biomass skimming. Yet, it has also been observed that flocculated biomass surrounding the biocatalysts were contributing in a large extent for the total immobilized biomass in the reactor. Thus, an assay testing the feasibility of flocculation as sole way of biomass immobilization in an airlift reactor was carried out. This new and simpler setup has shown much better performance than carriers’ based setups for biomass loading capacity (25 gcell dry wt..L-1), presenting very similar fermentation rates (rs = 3.4 g.L-1.h-1; and rp = 1.54 g.L-1.h-1). Then, two other continuous primary beer fermentations were carried out in order to test the feasibility and quality of beer produced using similar flocculation-based setups. In the first and longer fermentation up to 52 gcell dry wt..L-1 were attained through flocculation. Fermentation rates were higher than any other setup suggested by the literature for continuous beer fermentation (rs = 8.7 g.L-1.h-1; and rp = 3.7 g.L-1.h-1). This experiment was also very relevant as it was possible to correlate many other variables (such as FAN consumption rate influencing higher alcohols and diacetyl formation) contributing for the success of the suggested system. The last experiment was carried out at the laboratories of a large commercial brewery where some important parameters could be better controlled (fast feedback of results by automated beer analyzer, fresh wort always available, etc.). The results were consistent with the ones observed in the last mentioned experiment, replicating its outstanding performance (rs = 9.43 g.L-1.h-1; and rp = 3.75 g.L-1.h-1). Moreover, the beer from flocculated based setup was of excellent quality, confirmed by a professional panel of beer specialists. |
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