Reduction of Brettanomyces bruxellensis Populations from Oak Barrel Staves Using Steam

Abstract

Brettanomyces bruxellensis, a spoilage yeast associated with red wines, can be difficult to remove from oak barrels. New (16 L) and used (225 L) barrels representing French or American oaks with different toasting levels were obtained. A commercially-prepared Cabernet Sauvignon wine was transferred into the new barrels and inoculated with B. bruxellensis for six to seven months of aging. Upon disassembly of all barrels, yeast penetration was evaluated by collecting shavings from 2.5 cm diameter holes or by sawing staves into 3 × 10 cm blocks and then into 4 mm thick cross-sections. Additional blocks from the center of staves were exposed to steam for different times before being sawn into cross-sections. Shavings and cross-sections were transferred to either EBB enhancement (shavings) or wine recovery (cross-sections) media to detect culturable cells. In general, staves contained populations ≤10³ cfu/mm³ at depths up to 4 mm, with lower populations (≤10² cfu/mm³) occasionally detected between 5 to 8 mm depending on oak species or age of the barrel. During steaming, 2 to 3 min was required to achieve 55°C at a depth of 4.5 mm but slightly longer times were needed for 9.5 mm (≈4 min). Yeast present in 0 to 4 mm cross-sections required a total steaming time of 9 min for inactivation while 12 min was necessary for a depth of 5 to 9 mm. Because penetration depths in individual barrels are not possible to routinely determine by wineries, a minimum steaming time of 12 min can be used to limit future infections by B. bruxellensis in contaminated barrels.