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 levels (light or heavy) were infected with Brettanomyces bruxellensis. Infected staves were sawn into 3 cm × 3 cm cubes and immersed 2 mm into red wine (11% or 15% v/v alcohol) which had been heated to 35°, 40°, 45°, or 50°C. Upon removal from the wine, cubes were either sawn into cross-sections or prepared as oak shavings before transfer to a yeast recovery medium 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 while 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 or D_50°C =30 sec) compared to wines with 15% v/v alcohol (D_45°C =17 sec or 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 an alternate method to greatly reduce populations of B. bruxellensis if temperatures lower than those of hot water or steam are desired.