Chemistry of winemaking

A.Y. 2019/2020
Overall hours
Learning objectives
The course is aimed to give knowledges concerning the composition of grape and wine, the transformations occuring during the wine making, wine ripening and storage, the chemical practices during the wine making.
Expected learning outcomes
Students will be able to evaluate the effects of the wine making conditions and practices on the final product. He will be able to define the most suitable wine making practices to gain the final researched result.
Course syllabus and organization

Single session

Lesson period
First semester
Course syllabus
Structure of the grape berry tissue. General composition of the grape berry. Main families of compounds in the grape berry and notes concerning their role in oenology: hexoses, pentoses and polysaccharides, main organic acids. HTCA, anthocyanins and flavonoids, proanthocyanidins.
The acid balance in must and wine. The acid compounds in wine. Measure and calculation of acid forms.
Acidification and disacidification of wine. Factors affecting the tartaric stability o wine: pH, colloids, ethanol concentration. Principles of measuring the tartaric stability.
General aspects of terpene biosynthesis. Terpenoids: chemical structure, glycosylated froms, distribution in berry. Glycolytic enzymes in grape berry, in yeast, in bacteria, hexogen. Chemical structure modification and the role of pH, temperature and yeasts. Notes on terpene enrichment techniques of must and wine. The effect of wine filtration.
Flavouring compounds from carotenoids and the factors affecting their formation and build-up in grape and wine.
Metoxipyrazines from grape and Ladybug.
Thiol-related aroma compounds: precursors, their origin and modification in must and wine. The chemistry of volatile thiols. Fermentation and technologic factors affecting volatile thiols formation.
Correlation between YAN and yeast biomass. Timing of nitrogen addition and its effect on the cell growth. The role of ethanol on the nitrogen consumption ability of yeast. Nutritionally effective nitrogen forms. Fermentation flavouring compounds: higher alcohols and their formation. The flavouring role of higher alcohols. Lipid metabolism in yeast. Origin of saturated fatty acids and unsaturated phospholipids in the yeast cell: the role of oxygen. Acyltransferases, esterases and lipases and their role on the formation of flavouring esters. Esters stability.
Sulphur metabolism in yeast: the role of nitrogen and its supplementation, role of strain, elemental sulphur, glutathione, cysteine and pantothenenate. Source and role of thioesters. Role of malolactic bacteria. Post-fermentative effect of sulphite reductase enzyme. Source and role of DMS.
Oxygen activity and phenols. Chemistry of phenols: stability of the aromatic ring, the acid behaviour, the nucleophilic behaviour, the electronic stabilization in the reactions. Comparison of gallic and floroglucinolic phenols. Phenols of grape: HCTAs, flavanols, proanthocyanidins of stalks, skins and seeds. Anthocyanins and their acid behaviour.
The phenols extraction over the maceration: role of temperature, ethanol, mechanical force, placement in the berry. The straight co-polymerization of flavonoids.
Chemistry of oxygen in the oxidation reactions. Notes over the molecular orbitals. Redox potential of oxygen and wine solutes. Redox balances. The Fenton's reaction. Reactivity of quinones.
Aldehyde-bridged phenols polymerization, formation and stability of pyranoanthocyanins (flavanyl-piranoanthocyanins, pinotins, vitisins, portisins) and their role on the sensory properties (colour and astringency). The xanthylium salts. Special macerations for protecting anthocyanins. The role of wood phenols and flavanol composition of proanthocyanidins on red wine ageing.
Wood tannins and their interactions with oxygen and wine phenols. Oenology properties of oak wood. Wood flavouring compounds and their origin. Kinetics of oxygen entrance in wood barrel. The managing of barrelled wine.
Evolution of white wine: Maillard's reaction and its secondary compounds. Sotolone, aminoacetophenone, thiophenes. The role of glutathione, SO2 and yeast lees.
Origin and managing tools for Brettanomyces related-faults: volatile phenols, acetic acid, volatile aliphatic fatty acids, pyridines. Chemical tools for preventing, or cure, the barrelled wines.
Concepts concerning clarification and stabilization of wine. Role of the surface charge, z potential, hydrophobic interaction and hydration. Rational approach to wine treatment. Bentonite: properties, vantages and how to use. Adjutants for wine clarification and stabilization: proteins and synthetic compounds.
Cork stoppers: production, source of phenols and haloanisoles. Reduction wine faults from phytochemicals and lactic acid bacteria. The light-struck-taste: source and its prevention tools.
Prerequisites for admission
Teaching methods
Regular classroom lectures.
Teaching Resources
PowerPoint presentations showed during the lesson and available on the ARIEL web portal. References included in the slides.
Assessment methods and Criteria
Written exam at Asti consisting in three open questions to be completed by 2,25 hours. Students can also choose an oral trial at the university of Milano.
AGR/15 - FOOD SCIENCE AND TECHNOLOGY - University credits: 9
Lessons: 72 hours