The selection and breeding of brandy yeasts with enhanced ester formation
Du Toit, M A
University of Stellenbosch. Faculty of AgriSciences. Institute for Wine Biotechnology
Lambrechts, M G
Muller, C A
Gey van Pittius, M H
Strauss, M L A
The aim of this project is to find the most suitable yeast strain for the production of brandy wine spirits, bearing in mind not only the technical criteria stipulated for the production of an acceptable rebate wine, but also the best possible combinations of volatile compound interactions that may result in a top quality rebate wine and wine spirit.
There are unique methods and practices involved in producing an acceptable rebate wine for distillation into a brandy wine spirit. These include overnight settling of predominantly free run juice, no addition of sulphur dioxide during processing of grape must into wine, final total sulphur dioxide concentration in the rebate wine < 20 ppm and a final volatile acidity <0.7 mg/l. Furthermore, one must bear in mind that the double distillation procedure required for brandy spirits is essentially a concentration process (except for the compounds removed with the heads and tails fractions), in which all volatile and alcohol soluble compounds are concentrated in a final wine spirit of 70% v/v alcoholic strength.
The complexity of criteria and factors involved in such a multi-stage process like the production of brandy, have in the past made isolation of the optimal yeast strain to be involved in this process, very difficult.
In total one hundred and seven yeast strains (comprising commercially available strains, haploids from commercial strains and locally isolated yeast strains) were tested and screened for their respective ability to produce a brandy base wine of exceptional organoleptic quality during 1997 and 1998. Volatile acids, esters and fusel alcohols were quantified using gas chromatography. The results were interpreted using a multivariate analysis of variance (MANOVA) and an average linkage cluster analysis.
On the basis of their chemical profile, yeast strains exhibiting high concentrations of esters, low concentrations of higher alcohols and high concentrations of 2-phenethyl acetate, were selected and reevaluated in larger scale fermentations and subsequent double distillations. Sensory evaluations were performed on both the base wines and the final distillates using a panel that comprised tasters from three large brandy producing companies in South Africa.
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