Download or read book Characterization of Non-Saccharomyces Yeast to Reduce Ethanol Levels in Chambourcin Wine written by Lisa Tin and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Warmer climates and longer maturation periods have increased sugar accumulation in wine grapes over the past 30 years leading to higher ethanol levels in wines. Although other approaches have used pre-fermentation, post-fermentation, and vineyard management to reduce sugar concentration and consequently, reduce ethanol levels in wine, not all wineries have the resources to adopt these approaches. Previous studies have demonstrated that non-Saccharomyces yeasts when used in mixed fermentation, typically divided into co-fermentation (simultaneous inoculation of yeast strains) or sequential fermentation (one strain added after another), can reduce ethanol levels while enhancing flavor of final wines. While Saccharomyces cerevisiae is the standard yeast for wine fermentation due to its efficiency and reliability, the application of non-Saccharomyces yeasts as a simple and economical approach in mixed fermentations with S. cerevisiae to reduce ethanol levels in high °Brix wine grapes is not as well studied, especially in interspecific hybrid grapes. The overall goal of this project is to identify and characterize non-Saccharomyces yeast that can achieve greatest ethanol reduction when used in mixed fermentations with S. cerevisiae. Thus, we selected seven non-Saccharomyces yeast strains namely, Pichia kudriavzevii, Pichia kluyveri, Pichia terricola, Starmerella bacillaris, Hanseniaspora uvarum, Hanseniaspora opuntiae, LaktiaTM Lachancea thermotolerans for comparison against Saccharomyces cerevisiae EC-1118TM. In single inoculum and mixed fermentation with these yeasts, we used Chambourcin grapes, an interspecific French-American hybrid grape, because it is a commonly grown grape in the mid-Atlantic region within United States that has gathered interest as an alternative to Vitis vinifera grapes due to its higher resistance against cold temperatures and fungal diseases. In Aim 1, we characterized non-Saccharomyces yeasts based on their ability to tolerate varying concentrations of sulfite (0~100 mg/L free sulfur dioxide), conducted 3-day growth curves, as well as measured ethanol and sugar consumption levels in laboratory scale microfermentations as single strain inoculums. Based on this screening, we found that H. opuntiae, H. uvarum, P. kluyveri, and P. kudriavzevii strains performed the best in single strain fermentations. In Aim 2, we conducted 7-day mixed fermentations, either co- or sequential using H. opuntiae, H. uvarum, P. kluyveri, and P. kudriavzevii with S. cerevisiae EC1118. Based on this, we found that H. uvarum with S. cerevisiae EC1118 in co-fermentation and sequential fermentation had the lowest ethanol levels (co-fermentation, 86.28 g/L & sequential, 82.75 g/L), highest sugar consumption levels (242.40 g/L & 236.64 g/L), and lowest ethanol yield (0.356 & 0.349) when compared to S. cerevisiae EC1118 alone (ethanol levels, 101.28 g/L; sugar consumption levels, 242.60 g/L; ethanol yield, 0.383), suggesting production of other byproducts besides ethanol. However, when comparing mixed fermentation of H. uvarum with S. cerevisiae EC1118, sequential fermentation exhibited lower sugar consumption, ethanol levels, and ethanol yield while co-fermentation exhibited higher sugar consumption, ethanol levels, and ethanol yield after 7 days (p 0.05). Our results suggest that sequential fermentation is preferable for greater ethanol reduction with lower sugar consumption while co-fermentation is preferable for higher sugar consumption with moderate ethanol reduction. Finally, in Aim 3, we conducted mixed fermentations of H. uvarum with S. cerevisiae EC1118 in 22 °Brix (control) and 24 °Brix (treatment) Chambourcin juice. The goal of Aim 3 was to observe the differences in sugar consumption and ethanol reduction in the control and treatment Chambourcin juice. Despite the 2 °Brix increase based on 1:1.7 glucose to fructose ratio to the 22 °Brix juice, both mixed fermentations resulted in utilization of 98-99% of sugars by day 7, suggesting that NSY in mixed fermentation can successfully adapt to a higher °Brix juice and consume the majority of sugars with little to no residual sugars. However, because of the possibility of free SO_2 oxidation, which could increase the presence of spoilage microorganisms in the juice to initiate unwanted spontaneous fermentation before controlled fermentation, along with the small-scale fermentation and short fermentation time (mixed fermentations were not conducted to completion), no consistent significant differences (p 0.05) were detected in ethanol levels and yield between control and treatment. In addition, trends of ethanol levels and yield were not reproducible across two independent biological experiments, limiting our ability to draw conclusions on the ethanol reduction potential of H. uvarum in mixed fermentations using Chambourcin. Taken together, I conclude that H. uvarum with S. cerevisiae EC1118 can be used in mixed fermentation for potential ethanol reduction in Chambourcin wine. Mixed fermentation between S. cerevisiae and non-Saccharomyces yeast could be beneficial for the wine industry when dealing with higher sugar accumulation in grapes as a way to control ethanol levels in final wine. Future work should focus on optimization of fermentation conditions (extending fermentation until dryness), proper monitoring of free SO_2 during winemaking, and analysis of key chemical composition such as volatile acidity, glycerol, and organic acids in mixed fermentation.