Efficiency of alternative chemical and physical treatments in reducing Brettanomyces Bruxellensis from oak wood

Abstract

Oak barrels form an integral part of wine production, especially that of high quality wines. However, due to its porosity, wood presents an ecological niche for microbial proliferation and is highly susceptible to microbial spoilage which could cause considerable economic losses. Brettanomyces bruxellensis, the most commonly encountered microorganism responsible for spoilage during barrel ageing, can remain in barrels after barrel sanitation to contaminate new batches of wine after refilling. Therefore, effective sanitation treatments are of utmost importance to prevent recurring wine spoilage. Since a moratorium on the use of sulphur dioxide, the most widely used biocide for barrel sanitation, has been issued by the European Commission, there is a drastic need to evaluate alternative sanitation methods. Literature on the effectiveness of barrel sanitation treatments is scattered and presents inconclusive results. Furthermore, all studies have used culture-dependent methods to detect Brettanomyces which has been reported to attain a viable but non-culturable state [1,2]. Therefore, the aim of this study was to evaluate several physical and chemical sanitation treatments in their efficiency to eliminate B. bruxellensis from oak wood. French oak wood was contaminated with different B. bruxellensis strains and subsequently subjected to several chemical and physical sanitation treatments. The methods included, among others, ozone gas, ozonated water, high pressure ultrasound, steam, peracetic acid, sodium percarbonate and microwave. After their extraction from the oak wood, Brettanomyces cells were subjected to a fluorescence-based live/dead staining and detected by means of flow cytometry. The treatments differed greatly in their ability to reduce B. bruxellensis cells with ozone gas showing promising results. Sodium percarbonate and steam treatments were also effective in reducing cells. This study presents the first evaluation of alternative barrel sanitation treatments by flow cytometry, a culture-independent method, and is also the first study to compare an array of barrel sanitation treatments under controlled conditions.

1. Agnolucci, M., Rea, F., Sbrana, C., Cristani, C., Fracassetti, D., Tirelli, A., Nuti, M., 2010. Sulphur dioxide affects culturability and volatile phenol production by Brettanomyces/ Dekkera bruxellensis. International Journal of Food Microbiology 143, 76-80. 2. Serpaggi, V., Remize, F., Recorbet, G., Gaudot-Dumas, E., Sequeira-Le Grand, A., Alexandre, H., 2012. Characterization of the “viable but nonculturable”(VBNC) state in the wine spoilage yeast Brettanomyces. Food Microbiology 30, 438-447.