Indigenous wine killer yeasts and their application as a starter culture in wine fermentation

Wine yeast strains were isolated from seven fermentations of the red wines ‘Refošk’ and ‘Teran’, produced in the southwestern part of Slovenia. Among 613 isolated yeast strains, 22 expressed killer activity against the supersensitive strain Saccharomyces cerevisiae. Killer strains were isolated at different stages of wine fermentation but did not dominate in any of them. Species identification was based on the combination of RFLP analysis of an amplified rDNA region and biochemical–physiological tests. Killer isolates were identified as S. cerevisiae, Pichia anomala, Pichia kluyveri, Pichia pijperi, Hanseniaspora uvarum and Candida rugosa. Electrophoretic karyotyping was used to differentiate strains of the same species. Fermentation properties of four S. cerevisiae strains that possessed stable killer activity were characterized in fermentations of Malvasia must by studying their population dynamics and chemical composition and by sensory analysis of the wines produced. In order to compare the results, spontaneous fermentations and fermentations induced by commercial yeast starters were performed concomitantly. The local killer strain S_S12/10 showed the best fermentation properties and produced wine with favourable characteristics.