Enological microbiology

A.Y. 2018/2019
Lesson for
Overall hours
Learning objectives
Aim of the course is to give basic knowledge for understanding the identity, the physiological properties and role of microorganisms that play a role in wine chain. Object of study are yeasts and bacteria of main interest in the winemaking process, as well as the microorganisms that can modify the final product. Advancement of knowledge and applications to operate the control of safety and quality of wine and oenological products along the supply chain. Implementation of HACCP system in oenology. Risk assessment of the development of micro-organisms in wine production.
Tools to isolate, identify and to cultivate microorganisms of oenological interest to monitor microbiologically the winemaking process and to recognize and prevent wine spoilage. Knowledge of direct and indirect methods by using general and selective growth media to monitor the development of yeasts and bacteria. Evaluation of the role played by positive and negative microorganisms in the winemaking process. Management of the starter. Set-up of a hygiene system and quality assurance system into the cellar. Competence in the determination of microbiological safety and quality of wine and oenological products.

Course structure and Syllabus

Active edition
AGR/16 - AGRICULTURAL MICROBIOLOGY - University credits: 6
Laboratories: 16 hours
Lessons: 40 hours
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).
Teaching methods
Educational material provided by the professor.
Lesson period
First semester
Lesson period
First semester