UC Davis

Cleaning and sanitization are essential operations in wine production. The use of chemical cleaning and sanitizing agents for managing waste in fermentation vessels and the sulfur dioxide fumigation of empty oak barrels are ubiquitous processes in commercial wineries but are poorly studied in academic literature. Increasing environmental pressures and concerns over the poor quality of winery wastewater have created a need for optimizing protocols by reducing chemical inputs and water usage while maximizing the efficacy of treatments and employee safety during application. To optimize the use of chemical cleaning and sanitizing agents for managing fermentor waste the performance of a wide range of commercially available cleaning and sanitizing chemistries was assessed using fermentation derived soils and spoilage microorganisms in planktonic and sessile physiologies in trials from bench scale to 2000-L fermentation tanks. Minimum effective antimicrobial concentrations of chemical treatments were determined for common winery spoilage yeasts using the minimum inhibitory concentration, minimum biocidal concentration assay, and a modified minimum biofilm inactivation assay. Propidium iodide fluorescent staining was used to determine the minimum effective contact time required for inactivating Saccharomyces cerevisiae cultures using peracetic acid. Results suggested that caustic cleaning agents were the most effective in removing fermentation soils, and that sanitizers were ineffective without thorough prior cleaning. Peracetic acid- and hydrogen peroxide-based sanitizer formulations were effective and have innocuous breakdown products compared to traditional chemistries. Manufacturers’ suggested application rates were largely in line with the minimum effective antimicrobial concentration for the spoilage microorganisms tested. In practical settings, sanitary tank design may be the most important factor in determining the success of cleaning and sanitizing efforts regardless of the specific chemicals applied.The sulfur dioxide detection performance of colorimetric gas detection tubes, gas chromatography-sulfur chemiluminescence detection, and a novel electrochemical sensor apparatus was assessed. The electrochemical sensor was superior in linearity and precision versus the other detectors. American oak barrels were used to measure the persistence and antimicrobial efficacy of the sulfur dioxide fumigation of empty winery cooperage for pure gas application and the combustion of solid sulfur wicks. Prior to fumigation, the penetration rate and abundance of spoilage yeasts in barrel wood for cultures inoculated in grape must was determined for Saccharomyces cerevisiae and Brettanomyces bruxellensis cultures. S. cerevisiae cultures were recovered at 10 mm depth within one week of inoculation. B. bruxellensis cultures did not penetrate beyond surface samples within six weeks of inoculation. Measurable concentrations of sulfur dioxide existed after six weeks of storage for pure gas and sulfur stick fumigation, with concentration profiles closely described by power law functions regardless of the hydration status of the barrel wood. Both gas applications and sulfur stick combustion effectively eliminated culturable populations of S. cerevisiae and B. bruxellensis for all samples. Methods for assessing the mechanism of sulfur dioxide diffusion as a Fickian process according to the steady-state approximation poorly fit the measured gas data. Interactions between the diffusing gas and the stave wood and the heterogeneous structure of barrels may explain the discrepancy between the observed and predicted Fickian diffusive behavior. Together, this work presents the most comprehensive quantitative assessment of winery cleaning and sanitization to date in academic literature. These studies not only provide insight into the fundamental interaction of microorganisms, winery equipment, and chemical cleaners and sanitizers, but can also act as a practical resource for winemakers to develop effective cleaning and sanitizing protocols and monitoring strategies.