Botrytis cinerea and other bunch rot complexes : impact on musts and wines off-flavors

Botrytis cinerea and other bunch rot complexes : impact on musts and wines off-flavors

Stéphane La Guerche^1,3, Brunhilde Dauphin¹, Pierre Sauris²,
Dominique Blancard² and Philippe Darriet<sup>1

1</sup> UMR 1219 Œnologie, INRA, Institut des Sciences de la Vigne et du Vin, Université Victor Segalen Bordeaux 2, 351 cours de la libération, 33405 Talence, France, E-mail: [e-mail]

² INRA, UMR 103 Santé Végétale, ISVV, BP 81, 33883 Villenave d'Ornon, France

³ Bayer CropScience, 16 rue JM Leclair, CP 310, 69337 Lyon Cedex 09, France

The development of the fungal pathogen Botrytis cinerea on grapes is known to have a great importance on the flavor composition of musts and wines. When colonizing overmature, grapes berries and under specific climatic conditions, the fungus deeply modifies grape composition. This process identified as noble rot permits the elaboration of quality wines with complex and distinctive aroma. But usually, B. cinerea, is one of the major causes of damage of a number of grapes components and thus of deterioration in wine quality. During the recent years, several aromatic defects with a mushroom, moldy or earthy character combined with the more or less visible development of rots on grapes have been underlined in grapes and wines from various vine regions of France and Europe. The importance of these damages on the quality of wines from numerous cultivars (Cabernet Sauvignon, Semillon, Gamay, Chenin, Pinot noir) has led to a detailed study aiming first at the characterization of the compounds responsible for these off-flavors and secondly at the specification of their biological origin and the conditions of their expression in the vineyard.

Using various gas chromatography techniques, volatile compounds with mushroom, mossy, or earthy odors could be identified and were assayed in grapes and wines presenting these defaults. Some compounds as 2-heptanol, 2-octen-1-ol, 2-methylisoborneol, fenchol, fenchone, were detected in the grapes and musts but were not perceived in wines whereas others were present in grapes and musts and remained after alcoholic fermentation and could be prejudicial to the quality of wine [1-octen-3-ol, (-)geosmin]. Sometimes also, fungal compounds were found in wines at higher levels than in grape juice. (-) geosmin, with a powerful damp earthy, beetroot odor was the main defect found in numerous grapes and wines.

When analyzing the microflora present on rotten grape bunches, the presence of Botrytis cinerea was always evidenced. This fungus is known for its ability to produce the potent 2-methylisoborneol with earthy and camphoreous odor. But the main fungal off-flavors in wines were related to grapes presenting bunch rot complexes between Botrytis cinerea and secondary invaders belonging to various species especially from Penicillium genus. The implication of these fungi on the formation of several aromatic defects was analyzed. Particularly, through the study of (-)geosmin biosynthesis by Penicillium expansum, the biological and metabolic role of Botrytis cinerea in the bunch rot complexes was emphasized.