P.P. Minnaar, V. Paulsen, H. Du Plessis and N.P. Jolly
Post Harvest & Wine Technology, Agricultural Research Council, Stellenbosch, South Africa
Wine consumers predominantly use visual, aromatic and texture cues as quality/preference indicators to describe olfactory sensations. In this study the effect of micro-organism in wine production was investigated using analytical and sensory techniques to achieve relevant characterisation. Selected anthocyanins, flavanols, flavonols and phenolic acids were quantified in Syrah wines using RPHPLC- DAD. Standard oenological parameters and sensory attributes were also measured. Syrah grape must was fermented with various combinations of Saccharomyces cerevisiae (S. cerevisiae) and non-Saccharomyces (Metschnikowia pulcherrima or Hanseniaspora uvarum) yeasts, which was followed by sequential inoculation with lactic acid bacteria (LAB) [Oenococcus oeni or Lactobacillus plantarum]. Phenolic, sensory and oenological data were positively correlated where the phenolic data differentiated S. cerevisiae yeast, non-Saccharomyces yeast and LAB. Increased phenolic compound concentrations were evident in Syrah wines made with a combination of S. cerevisiae, non-Saccharomyces and LAB, compared to wines made with S. cerevisiae only. Wines produced with S. cerevisiae, M. pulcherrima and O. oeni (LAB) were higher in flavanols, flavonols and phenolic acid concentrations compared to the control wines that were produced using S. cerevisiae yeast only. Syrah wines made with S. cerevisiae, M. pulcherrima and L. plantarum were higher in total anthocyanins, compared to wines inoculated with S. cerevisiae only. The wine sensory attributes, body and astringency correlated positively with a combination of yeast and LAB treatments. Wines made with a combination of yeast and bacteria also scored highest in overall wine quality. It was shown that S. cerevisiae retained more phenolic compounds during fermentation when compared to wines made with a combination of yeast and LAB treatments during fermentation. Wines produced with non-Saccharomyces yeasts combinations contained lower alcohol levels, compared to wines produced with S. cerevisiae only. None of the treatments produced high volatile acidity levels.
Keywords: Yeast, lactic acid bacteria, phenolics, sensory attributes.