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 6 to 7 mos of aging. Upon disassembly of all barrels, yeast penetration into the wood 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 enhancement (shavings) or wine recovery (cross sections) media to detect culturable cells. In general, staves contained populations of ≤10³ cfu/mm³ at depths up to 4 mm, with lower populations (≤10² cfu/mm³) occasionally detected between 5 to 8 mm, depending on the oak species or barrel age. 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, whereas 12 min was necessary for a depth of 5 to 9 mm. Because it is not possible for wineries to routinely determine yeast penetration depths in individual barrels, a minimum steaming time of 12 min can be used to limit future infections by B. bruxellensis in contaminated barrels.