Analysis of grapes and the first stages of the vinification process in wine contamination with Brettanomyces bruxellensis

Brettanomyces bruxellensis is a major cause of wine spoilage due to the production of ethyl phenols, and it has become a major worldwide oenological concern in recent years. The most critical factor in volatile phenol production is the presence of microorganisms responsible for biosynthesis. In this work, carried out during three consecutive harvests, grapes and the first step in grape processing (stemming–crushing) have been evaluated as the origin of wine contamination by these spoilage yeasts. Results showed that there was nil or minimal presence of Brettanomyces yeasts in grapes and on the stemmer, in levels that the method was not able to detect. This shows that the main contamination of wines by this microorganism occurs in later stages of the vinification process and/or during storage. The contamination of many wines with Brettanomyces, either via the fruit or from the winery environment, during the early stages of vinification and before the start of aging, was confirmed by analyzing 100 recently made red wines, in which this yeast was detected in a high percentage of wines (27 %). However, the level of Brettanomyces yeasts found in the samples was low, with values which would not be sufficient to cause organoleptic defects. Consequently, this study confirms that many wines are still tainted by Brettanomyces when the winemaking phase comes to an end. It was also found that wines with problems during fermentation had a higher level of Brettanomyces. This is why it is essential to ensure strict controls during fermentation processes and conservation to prevent wine becoming spoiled or tainted.