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

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:

• Overall, the blended yeasts performed better than a standard addition of SO₂ at controlling wine spoilage organisms on compromised fruit.

• 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.

• 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.

• 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.

• 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:

• A reduction in spoilage microorganisms occurred when using Td/Mp directly applied to the harvester.

• 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.