Enological microbiology

A.Y. 2020/2021
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.
Expected learning outcomes
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 syllabus and organization

Single session

Lesson period
First semester
In order to ensure the educational offer to all students in compliance with the restrictions set by the regulations on COVID 19, the lessons will be held synchronously through the Microsoft Teams platform in accordance with the teaching calendar. At the same time, audio and video recordings of the lessons will be made available to students asynchronously through the Ariel platform and/or Microsoft Stream.
In addition, the course will include 8 hours in presence in classroom and 4 hours in presence of the laboratory. Students can choose to participate by registering through the booking application made available by UNIMI. These meetings will have the dual purpose of (1) discussing the topics addressed in the previous lessons by answering any questions and solving any doubts, and (2) deepening the topics covered in the previous lessons through an open discussion on selected scientific literature previously provided to students by the teacher.
Type of exam: oral exam. Microsoft Teams platform must be used. It is mandatory the registration to the exam via the UNIMIA service.
Course syllabus
Frontal lessons:
1. Taxonomy and ecology of the wine yeasts. Classification criteria and wine yeast ecology: the different yeast species in must and wine;
2. Yeast cell structure and the morphological characteristics of wine yeasts;
3. Carbon metabolism in yeast and its regulation: Pasteur, Crabtree and Custer effects (Brettanomyces: a case of study);
4. Nitrogen metabolism in yeast;
5. Sulfur metabolism in yeast;
6. Microbiological analysis at different stages of vinification;
7. Microbiological control of must and Spontaneous fermentations;
8. Growth kinetics of yeasts and factors affecting yeast growth during fermentation;
9. Controlled fermentations and the selection of commercial wine yeast: selection and management of the starter yeast selection for technological characteristics and quality traits. The fermentative power and vigour, Alcohol tolerance, SO2 resistance, Killer character and yeast proliferation;
10. Yeast starter cultures and their usage: isolation, control and maintenance of a pure culture of yeast (the laboratory phase, the phase of the cellar, the direct inoculation). The types of commercial starters. The operation for starter management;
11. Genetic improvement of wine yeasts: Yeast genome organization, The life style of Saccharomyces cerevisiae, Yeast genetics: heterotallic and homotallic yeast strain. The genetic interconversion phenomena;
12. 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;
13. Microbiological aspects of stuck fermentation;
14. Sparkling wines and Yeast autolysis;
15. Microbiological stabilization techniques for wine;
16. Hygiene and Good Hygienic Practices in cellar;
17. The HACCP method and the application of the hygiene system;
18. The manual of good practice for the wine industry;
19. Sources of contamination in the cellar. Sanitation of equipment and facilities. Detergents and disinfectants. Water management process.

Laboratory class:
1. Determination of yeasts in a fermenting grape must (enumeration of non-Saccaromyces species and S. cerevisiae). Microscopic observations: morphological traits of wine yeasts;
2. Checking the hygiene of personnel and of surfaces by the use of Petri-Contact;
3. Microbial air monitoring;
4. Fermentative power and vigour of a commercial wine yeast;
5. Analysis of a commercial wine yeast: determination of the total yeast count using a cultural method and the microscopic observation with counting chamber;
6. Analysis of the technological traits of a wine yeast: H2S production;
7. Microbiological stability of bottled wine with plate count technique and filtration: determination of malolactic bacteria, determination of B. bruxellensis and acetic bacteria;
8. Microbiological control of drinking water;
9. Assessing the contamination of a bottle cork cap;
10. Assessing the flocculation character of a wine yeast.
Prerequisites for admission
The course of Microbiology is propedeutic. The notions acquired during the course of Biochemistry are considered useful.
Teaching methods
Teaching is provided through frontal lessons and a laboratory class. Laboratory attendance is not mandatory; however, the concepts associated with this activity may be the subject of questions in the written test.
Teaching Resources
Teaching material available on Ariel. Furthermore, use the "Manual of good hygiene practice for the wine sector".
Teaching text: M. Vincenzini, P. Romano, G.A. Farris. "Wine microbiology". Ambrosiana Publishing House, Chapter 1 (1.3: 1.3.1-1.3.6); Chapters 3 to 6; Chapters 8 to 13; Appendix I and II.
Alternatively: G. Suzzi and R. Tofalo. "Oenological Microbiology". Edagricole
Assessment methods and Criteria
Type of exam: written test organized in open-ended questions; effective duration of 66 minutes. The exam is unique and includes questions regarding both the topics covered by the frontal lessons and the laboratory class. Registration to the exam session by UNIMIA system is mandatory.
Evaluation parameters: demonstration of acquisition of the concepts; ability to organize knowledge; correct use of the specialized vocabulary.
Evaluation: mark out of thirty.
AGR/16 - AGRICULTURAL MICROBIOLOGY - University credits: 6
Laboratories: 16 hours
Lessons: 40 hours
Professor: Vigentini Ileana
Educational website(s)