Winemaker’s Bookshelf


They play a significant role in the sensory properties of wine, especially astringency andmouthfeel.


F


ormany of us, the term flavonoid elicits aMEGO response . . .My Eyes Glaze


Over. This is not the kind ofmaterial I can absorb in a single reading. The flavonoids are divided into


threemajor subclasses: anthocyanins, flavonols, and proanthocyanidins (also called condensed tannins). Over 6,000 flavonoid compounds have been described in the literature, thus an appreciation beyond the generalities is left to specialists in the field. In the following discussion


I’ve attempted to relate flavonoid chemistry to the practical fields of growing grapes andmaking wine. For winemakers, a


rudimentary knowledge of flavonoid chemistry is important for the development of colour and palate in both red and white wines, even though day to day attention is focused on the practical applications of the science. By extension, the development and


maturation of grape flavonoids pre- harvest is important for the understanding of optimal grape varietal character. For the general public, the


biological role of flavonoids is now recognized to be responsible formany of the health-enhancing benefits of wine, fruits, vegetables and nuts. Some nutrition experts have even recommended that aminimum- intake dietary recommendation be established for flavonoids andmore broadly for phenolic compounds, similar to vitamins and other food components. The Science of Flavonoids (0-387-


28821-X) presents an overview of flavonoid nomenclature, chemistry, synthesis, and health benefits. I like the way in which the book is


By Gary Strachan Finding favourite flavours of flavonoids


organized. It opens with an examination of flavonoids fromthe stereochemical point of view. The emphasis in this chapter is on the synthesis of flavonoids via asymmetric catalysis of reactive groups on themolecules. As a


winemaker, I relate to this discussion because of the importance of copigmentation for colour development. Stereochemistry enables us to


visualize the three-dimensional world of winemaking at themolecular level. The book continues into a level of chemistry that few of us have or will


produce consistent phenolic composition, especially in a climate as varied as British Columbia’s. Flavonoids and the various


reactions and polymerizations that they are involved in play a significant role in the sensory properties of wine, especially astringency andmouthfeel. There are interesting chapters on


the evolution of flavonoids and the genes responsible for their biosynthesis. For example, the function of flavonoids is thought to have been diverted when plants evolved onto growth on land. Flavonoids evolved as protection


against UV light, defence against predators and pathogens, and recruitment of pollinators and seed dispersers. Flavonoids are important


experience; the chemical synthesis, isolation and characterization of flavonoids. Further chapters describe how


flavonoids are biosynthesized and how that synthesis is regulated. This area is important to us as winemakers because we understand flavonoids to be secondarymetabolites but we have only a vague notion of what wemust do to achieve the levels important to good winemaking. In the vineyard we recognize that each stage of maturity plays a role in development of phenolic compounds, along with the development of varietal flavours. Astringency and phenolic flavours vary among grape varieties and are affected by vineyard location and management techniques, but we have much to learn about accurate management of the factors that


in seed fertility, in themediation of interactions between plants and other organisms in the community, both in defense frominfection and in synergistic cooperation (as with mycorrhizae). Wemake practical use of these


properties when we ensure light exposure for leaves and fruit in the vineyard, a practice that favours flavonoid development as the plant’s defence against UV injury of cells. The flavonoids are a diverse group


of compounds as synthesized biologically, and the number of potential compounds derived from themincreases even further during winemaking because of their chemical reactivity. Every time we transfer wine


production fromoxidative to reductive conditions and back again,


British Columbia FRUIT GROWER • Summer 2013 31


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