Brettanomyces bruxellensis is a yeast often associated with spoilage during barrel aging of wines. It is therefore important that the wine industry develops more efficient oak sanitation protocols to avoid contamination by this microorganism. This requires a consensus regarding to what depths this yeast can be found in barrel staves. The penetration of B. bruxellensis into oak staves with different oak type, toasting level, and physical location within a barrel was studied. For the experimental design, 16-L barrels made from French or American oak (Q. petraea or Q. alba, respectively) and processed with two different toasting levels were obtained. The barrels were infected with B. bruxellensis for seven months with one un-inoculated barrel of each type serving as controls. Once emptied, the barrels received a hot water/SO₂ rinse before being disassembled. Individual staves were cut into 3 x 10 cm blocks before being subdivided into four mm thick layers (inside to outside of barrel). These layers were placed in a sterile-filtered, nutrient-enriched wine to recover any viable cells present. Additional layers were observed under scanning electron microscopy (SEM) to compare oak structure and yeast infiltration. Key findings included differences in B. bruxellensis recovery from the two types of oak studied. The furthest penetration occurred in French oak staves located at the bottom of barrels between five to nine mm. Additionally, yeast populations from heavy toasted staves tended to enter logarithmic growth more quickly. SEM images agreed with the recovery data and suggested possible pseudohyphae formation by this yeast. Our research demonstrates that B. bruxellensis oak contaminations differ with respects to oak species, toasting level, and stave location. Knowing the depths of yeast infiltration, better protocols to eliminate B. bruxellensis from contaminated barrels can now be investigated.

Funding Support: Wine Advisory Committee of the Washington Wine Commission, Agricultural Research Center, WSU-CAHNRS