Previous studies have shown the importance of ethanol and sulfur dioxide production by Saccharomyces cerevisiae on the growth of Oenococcus oeni. Our goal was to examine other interactions between these organisms, including competition for nutrients and production of microbial inhibitors, and their relative importance in winemaking. Fourteen strains of S. cerevisiae commonly used in vinification and 16 strains of O. oeni were studied. To better replicate conditions of winemaking in the laboratory, natural grape juices were fermented with the different yeasts, followed by inoculation of the bacterial strains into the wines. Bacterial growth and malate depletion were monitored in the wines. Results from these fermentations were compared to industry trials and to interactions observed on agar plates. The relationship between growth and malolactic activity in O. oeni is important to the discovery of a simple method for identification of positive and negative interactions between yeast and bacteria. Many strains performed malolactic fermentation without growing in the wine. Most plating methods rely on growth of the bacteria and will not be successful predictors of compatible pairs when the bacteria do not require growth for malolactic activity. The plating method described here is useful for differentiating between effects of yeast on O. oeni due to nutrient competition and effects due to production of inhibitory compounds. Eighty-eighty percent of the wines showing negative growth effects on plates also resulted in unsuccessful malolactic fermentation in the laboratory-scale wines. We recommend that you read the full text of this article, which was published in the American Journal of Enology and Viticulture 56: 228-237. Follow the link on the right to find the full text of this paper.