Heat inactivation of wine spoilage yeast Dekkera bruxellensis by hot water treatment.

Abstract

Cell suspensions of four Dekkera bruxellensis strains (CBS 2499, CBS 2797, CBS 4459 and CBS 4601) were subjected to heat treatment in deionized water at four different temperatures (55·0, 57·5, 60·0 and 62·5°C) to investigate their thermal resistance. The decimal reduction times at a specific temperature were calculated from the resulting inactivation curves: the D-values at 55·0°C ranged from 63 to 79·4s, at 57·5°C from 39·6 to 46·1s, at 60·0°C from 19·5 to 20·7s, at 62·5°C from 10·2 to 13·7s. The z-values were between 9·2 and 10·2°C, confirming that heat resistance is a strain-dependent character. A protocol for the sanitization of 225l casks by immersion in hot water was set up and applied to contaminated 3-year-old barrels. The heat penetration through the staves was evaluated for each investigated temperature by positioning a thermal probe at 8mm deep. A treatment at 60°C for an exposure time of 19min allowed to eliminate the yeast populations up to a log count reduction of 8. Brettanomyces/Dekkera bruxellensis is the main yeast involved in red wine spoilage that occurs during ageing in barrel, generating considerable economic losses. Current sanitization protocols, performed using different chemicals, are ineffective due to the porous nature of the wood. The thermal inactivation of D.bruxellensis cells by hot water treatment proves to be efficacious and easy to perform, provided that the holding time at the killing temperature takes into account the filling time of the vessel and the time for the heat penetration into the wood structure.