Prediction of Effective Steam Sterilization Times for Wine Barrels Using a Mathematical Modeling Approach

Oak barrels are often used to flavor and color wine, beer, and distilled beverages. However, microorganisms can penetrate into the wood, making cleaning and sterilization difficult. This can lead to undesired microbial growth in the contents of the barrel during subsequent use. Information on heat penetration into barrel staves during steam treatment and associated thermal inactivation rates is scarce. Therefore, we incorporated heat transfer and Arrhenius-type death kinetics to build a mathematical model to predict the killing rate of the microorganisms when steam sterilizing a wooden barrel. First, we used this model to predict temperature profiles in barrel staves as a function of distance from the steamed surface and time of steaming. We then evaluated the thermal inactivation of microorganisms at 0.8 cm into the stave (the maximum wine penetration depth into a stave) to calculate the time needed to achieve a 5-log reduction in live cells. Using this approach, we found that the required sterilization times for Brettanomyces bruxellensis, Saccharomyces cerevisiae, and Leuconostoc mesenteroides are 9 min, 12 min, and 200 min, respectively. This result is useful for winemakers to determine how long they desire to steam a barrel to prevent growth and contamination of key microbes in their wine.