Microflora Across Maryland Vineyards: Public Health Considerations and Applications in Wine Fermentation

Abstract

Viticulture, the study of grapevine production, has expanded across the United States of the pastseveral decades. The present work investigated aspects of viticulture production in Maryland, including the relationships between the dynamic chemical and microbial quality of wine grapes grown in this region, how the grape-associated microflora may have implications for One Health considerations, and how wild yeasts can be leveraged in wine fermentation. First, a survey of Maryland vineyards (n=4) was conducted in 2024 and 2025, examining longitudinal changes in microbial populations present on wine grapes alongside the development of chemical properties indicative of ripening (i.e., pH, °Brix) in three different grapevine cultivars (Cabernet Franc, Chambourcin, Chardonnay). All measured parameters shifted throughout the respective growing seasons, and varied based on cultivar, site, and year. Additionally, native yeasts representing potential emerging health threats (i.e., Candida auris) and those involved in wine fermentation were recovered with different enrichment techniques. Collectively, these yeast isolates were identified as Hanseniaspora uvarum (n=10), Meyerozyma guilliermondii (n=14), Pichia kudriavzevii (n=5), and Zygoascus meyerae (n=2), Candida tropicalis (n=2), and other Saccharomycetales (n=4). All isolates were confirmed negative for C. auris via PCR, and the fermenting isolates demonstrated growth in simulated grape juice media. Select strains of oenologically relevant native yeasts, P. kudriavzevii and H. uvarum, were further examined in microvinification-scale fermentation of Cabernet Franc grape must (i) individually, (ii) as co- inocula with S. cerevisiae, and (iii) as starter cultures in sequential inoculations with Saccharomyces cerevisiae (i.e., introduced after 7 and 14 days). Differences in the fermentation kinetics, alcohol production, and pH were observed, suggesting potential impact on final wine composition. Overall, this work advances the understanding of microbial relationships within viticulture systems in the mid-Atlantic region and provides a foundation for future studies to explore how NS yeasts may enhance wine fermentation and sensory perception.