Innovative Use of Non-Saccharomyces in Bioprotection: T. delbrueckii and M. pulcherrima Applied to a Machine Harvester

Summary Goals: This study addresses the increasing demand for ‘natural’ and certified ‘organic’ wines, along with the need for improved worker safety. Winemakers continue to search for alternatives to SO2 as an antioxidant and anti-microbial agent. This study compares the use of blended non- Saccharomyces cerevisiae yeasts, Torulaspora delbrueckii (Td) and Metschnikowia pulcherrima (Mp) as anti-microbial agents to a standard addition of SO2 on Cabernet Sauvignon. This fruit possesses over ten times the normal microbial flora typically found in California. In conjunction with this comparison study, a proof of concept prototype illustrates the use of a novel spray method for the application of these non-Saccharomyces yeasts onto a grape machine harvester for bioprotection. Key Findings: Research Winery: 30 Overall, Td/Mp performs better than a standard addition of SO2 at controlling wine 31 spoilage organisms on compromised fruit. Organisms related to wine spoilage respond differently to Td/Mp vs. SO2. The Td/Mp treatment exhibits an advantage over the SO2 treatment. The Td/Mp treatment appears to work best against: Zygosaccharomyces, Lactobacillus kunkeei, Hanseniaspora uvarum, and acetic acid bacteria. It is less effective against Pediococcus and other Lactobacillus species. Different stages of the trial fermentations are affected differently using Td/Mp vs. SO2. The Td/Mp populations perform best during prefermentation and the early stages of the fermentation. Td/Mp illustrates an antagonistic effect on micro-organisms responsible for wine spoilage. There are fewer micro-organisms related to spoilage growing in the three bio-reactors with non-Sac species than in the bio-reactors acting as experimental control with 60 mg/L SO2 added during processing. Td/Mp treatment increases the implantation capacity of S. cerevisiae compared to the use of SO2. Using identical inoculation rates of S. cerevisiae, we find more cells of S. cerevisiae growing in the Td/Mp bioreactors than in the bioreactors treated with SO2. Furthermore, we observe larger amounts of population reduction and fewer cells/mL of S. cerevisiae during the end of fermentation. Field Trial: A reduction in spoilage micro-organisms occurs when using Td/Mp directly applied to the harvester. Applying Td/Mp yeasts to the grape harvester reduces aromas related to Volatile Acidity coming from the machine. Impact and Significance: Using Td/Mp yeasts provides an alternative to SO2 for controlling the growth of organisms related to wine spoilage. Incorporating these yeasts as a bio-protectant by applying the yeasts during the harvesting and transport processes reduces the risk of detrimental microbial organisms in the harvested fruit, juice, and wine during processing.