Enological Microbiology

1. Taxonomy and ecology of the wine yeasts. Classification criteria. The different yeast species in musts and wines: yeasts in winery and fermentation. The Saccharomyces sensu stricto group. Morphological characteristics of wine yeasts. Methods of yeasts isolation, identification and characterization of microorganisms of oenological use. Identification systems based on the analysis of the phenotype and genotype. Using miniaturized systems for microbial identification based on analysis of the phenotype. Theory and applications of PCR. The genotyping techniques. 2. Primary metabolism and its regulation: Pasteur, Crabtree and Custer effects. Nitrogen, sulfur compounds and organic acids metabolism. Formation of sulfur compounds. 3. Growth kinetics of yeasts and factors affecting yeast growth during fermentation. Microbiological analysis at different stages of vinification. Microbiological control of must (determination of S. cerevisiae yeast contaminants, acetic acid bacteria and lactic acid bacteria by plate count technique). Control of the fermenting must (enumeration of S. cerevisiae with counting chamber, dying and microscopic observations, determination of Saccharomyces by membrane filter technique). Sparkling wines and Yeast autolysis. The yeast of maloalcholic fermentation. 4. Spontaneous and controlled fermentations. Yeast starter cultures and their usage. Yeast genome organization. The life style of Saccharomyces cerevisiae. Yeast genetics: heterotallic and homotallic yeast strain. The genetic interconversion phenomena. Genetic improvement of wine yeasts. Selection and management of the starter yeast selection for technological characteristics and quality traits. The selection by territories, the selection through genetic improvement. Isolation, control and maintenance of a pure cultures. Determination of the fermentation, assessing the flocculation character, H2S production, killer character. The types of commercial starters. The operation for starter management. The techniques of multiplication and maintenance (the laboratory phase, the phase of the cellar, the direct inoculation). Microbiological aspects of stuck fermentation. 5. Lactic acid bacteria (LAB) in musts and wines and their interaction with yeasts during alcoholic fermentation. Metabolism of sugars, organic acids and aminoacids. Effect of ethanol and temperature on the LAB growth. Spontaneous and controlled malolactic fermentation. Malolactic starter cultures. Isolation, control and maintenance of a pure culture of malolactic bacteria. Determination of malolactic bacteria with plate count technique. Good Manufacturing Practices in cellar. The HACCP method and the application of the hygiene system. The manual of good practice for the wine industry. Sources of contamination in the cellar. Sanitation of equipment and facilities. Detergents and disinfectants. Water management process. Checking the personal hygiene and surfaces by the use of Petri-Contact and Swab Test. The bioluminescence technique. Microbial air monitoring. Microbiological control of drinking water. Compliance of bottle caps and corks. The bottling. Wine spoilage by LAB, acetic bacteria and yeasts. Sulphur dioxide and wine microorganisms. Control of stability of the bottled wine (membrane filtration and microscopic observation in epifluorescence).