Efficacy of Warmed Wine Against Brettanomyces bruxellensis Present in Oak Barrel Staves

Abstract

New barrels (16 L) differing by oak species (Quercus alba or Q. petraea) and toasting level (light or heavy) were infected with Brettanomyces bruxellensis. Infected staves were sawed into 3 cm × 3 cm cubes and immersed 2 mm into red wine (11 or 15% v/v alcohol) that had been heated to 35, 40, 45, or 50°C. After removal from the wine, cubes were either sawed into cross sections or prepared as oak shavings before transfer to a yeast recovery medium and incubated for ≥30 days (cross sections) or for 12 hr (shavings) to recover culturable populations and calculate decimal reduction times (D_T-values). Culturable cells were not recovered from inner cross sectional layers (0 to 4 mm depth) after heating in 11% v/v alcohol wine at 45 or 50°C, whereas populations were destroyed at deeper depths (e.g., 5 to 9 mm) using wines of 15% v/v alcohol at these same temperatures. In agreement, D_T-values were greater when cubes were heated in 11% v/v alcohol wines (D_45°C = 46 sec, D_50°C = 30 sec) compared to wines with 15% v/v alcohol (D_45°C = 17 sec, D_50°C = 9 sec). Compared to heated water or steam, warmed-wine treatments required lower temperatures to remove the same degree of microbial contamination, in particular at inner stave depths ≤4 mm. Similar observations were noted for commercial barrels (225 L) previously infected by unidentified (in-house) strains of B. bruxellensis. Thus, application of warmed wine to infected barrels may serve as a method to greatly reduce populations of B. bruxellensis when temperatures lower than those needed for hot water or steam treatment are desired.