This study aims to understand the effect on micro-organisms of racking when the wine is aged in barrels. According to the kind of micro-organism, the effects are different. Bacteria are stimulated by oxygen and their population increases. Yeasts are concentrated to the bottom of the barrel. Between two successive rackings, a yeast population gradient was established. Yeast cells which are larger and heavier than bacteria cells are deposited on the barrel bottom with other wine micro-particles. In some cases, the yeast population at the bottom was more than one thousand times greater than at the wine surface. Moreover, the species identified at different heights in the barrel were different. Saccharomyces cerevisiae was the main yeast detected at the surface, whereas Brettanomyces bruxellensis was the main yeast found in the lees. After racking, yeast populations decrease because they are eliminated with the lees during the operation. Among them, Brettanomyces bruxellensis was found in the greatest numbers. Since they are able to produce volatile phenols, their preservation in the barrel can lead to alteration of the wine. Indeed, the ability of the lees to produce volatile phenols was clearly established. The importance of regular racking for microbial wine stabilization is evident. The risks of "sur lies" wine aging and stirring operations are emphasized. We recommend that you read the full text of the article from which this abstract is taken. Original title: Les soutirages sont des étapes clefs de la stabilisation microbiologique des vins. Source: Journal International des Sciences de la Vigne et du Vin, 38 (4) 219-224 (2004).