Recombinant DNA technology has allowed for improvement of yeast strains used in brewing and wine-making with significant advances in process performance. Traditionally mutagenesis, hybridisation, protoplasm fusion and cytoduction were used to modify yeast traits followed by selection for qualities favourable to beverage fermentation. Advances in gene technology now allow the modification of targeted characteristics without affecting the existing desirable traits.
Yeasts commonly used in brewing and wine-making are strands of S. cerevisiae. Interestingly, this yeast was the first eukaryotic microorganism to have its genome fully sequenced. Differences are apparent however, in the industrial strains often used in beverage fermentation compared to the sequenced laboratory strains.
Process performance of wine-making and brewing techniques was enhanced by genetically assisted flocculation. Yeast flocculation involves asexual aggregation of cells into flocks and their removal by the process of sedimentation. This is an important process in brewing as good flocculation ensures bright beer with sufficient aroma. Flocculation also shows possible advantages to use in the elaboration of sparkling wines. At present a lengthy and expensive process of secondary fermentation is used whereby yeast cells are removed by "remuage" after one year. Sedimentation of flocculent yeast cells would greatly improve this process by optimising time and cost.
The dominant flocculat
ion gene FLO1 encodes for a cell wall protein. A vector containing this gene has been removed from a flocculent S.cerevisiae strain and successfully transferred into a wine yeast strain. Non-flocculent brewer's yeast has also been transformed by the ADH1 regulated FLO1 gene by integration into the ADH1 locus. This transformation resulted in strong flocculation in this recombinant yeast however, due to a lack of regulated promoters, it occurred too quickly resulting in inefficient maturation of the beer.
ion gene FLO1 encodes for a cell wall protein. A vector containing this gene has been removed from a flocculent S.cerevisiae strain and successfully transferred into a wine yeast strain. Non-flocculent brewer's yeast has also been transformed by the ADH1 regulated FLO1 gene by integration into the ADH1 locus. This transformation resulted in strong flocculation in this recombinant yeast however, due to a lack of regulated promoters, it occurred too quickly resulting in inefficient maturation of the beer. It is apparent that gene technology serves a purpose in the wine-making and brewing processes although more research is needed to control and enhance the effectiveness of this resource.
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