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 antimicrobial agent. This study compares the use of blended non-Saccharomyces cerevisiae yeasts—Torulaspora delbrueckii (Td) and Metschnikowia pulcherrima (Mp) — as antimicrobial agents to a standard addition of SO2 on Cabernet Sauvignon. This fruit possesses over 10 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
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Overall, the blended yeasts performed better than a standard addition of SO2 at controlling wine spoilage organisms on compromised fruit.
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Organisms related to wine spoilage responded differently to Td/Mp than to SO2. The Td/Mp treatment exhibited an advantage over the SO2 treatment. The Td/Mp treatment appeared to work best against Zygosaccharomyces, Lactobacillus kunkeei, Hanseniaspora uvarum, and acetic acid bacteria. It was less effective against Pediococcus and other Lactobacillus species.
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Different stages of the trial fermentations were affected differently by Td/Mp and SO2. The Td/Mp populations performed best during prefermentation and the early stages of fermentation.
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Td/Mp showed an antagonistic effect on microorganisms responsible for wine spoilage. There were fewer microorganisms related to spoilage growing in the three bioreactors with non-Saccharomyces species than in the bioreactors acting as experimental controls with 60 mg/L SO2 added during processing.
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Td/Mp treatment increased the implantation capacity of S. cerevisiae compared to the use of SO2. Using identical inoculation rates of S. cerevisiae, we found more S. cerevisiae cells growing in the Td/Mp bioreactors than in the bioreactors treated with SO2. Furthermore, we observed greater population reduction and fewer cells/mL of S. cerevisiae at the end of fermentation.
Field Trial
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A reduction in spoilage microorganisms occurred when using Td/Mp directly applied to the harvester.
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Applying Td/Mp yeasts to the grape harvester reduced aromas related to volatile acidity coming from the machine.
Impact and Significance:
The use of Td/Mp yeasts provides an alternative to SO2 for controlling the growth of organisms related to wine spoilage. Incorporating these yeasts as a bioprotectant by applying them during the harvest and transport processes reduces the risk of detrimental microbial organisms in the harvested fruit, juice, and wine.
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