Jared Johnson, Mengying Fu, Michael Qian, and James Osborne*
*Oregon State University, Wiegand Hall, 3051 SW Campus Way, Corvallis, OR 97330 (james.osborne@oregonstate.edu)

Hanseniaspora uvarum is often the most abundant yeast present on grapes at harvest and is a primary source of volatile acidity during cold soak. H. uvarum growth during cold soak is typically controlled using sulfur dioxide and by maintaining grapes at a cold temperature. While effective, these methods can also restrict the growth of other, non-Saccharomyces yeast present during cold soak that can contribute positively to wine aroma. Recently, addition of select non-Saccharomyces yeast at the beginning of cold soak has been suggested as an alternative method to reduce volatile acidity. This study investigated the efficacy of select non-Saccharomyces yeast strains to reduce volatile acidity and H. uvarum growth during cold soak. Commercially available non-Saccharomyces yeasts were screened for their ability to reduce H. uvarum growth and acetic acid production during a simulated cold soak in a grape juice-based medium. H. uvarum growth and acetic acid production was reduced in the presence of all non-Saccharomyces yeast tested, with some yeast having a greater impact than others. One yeast, Metschnikowia fructicola, was then used in Pinot noir winemaking experiments. Pinot noir grapes were inoculated with a combination of H. uvarum and M. fructicola, then cold-soaked for six days. During cold soak, M. fructicola reduced H. uvarum growth and significantly decreased acetic acid and ethyl acetate production. These results suggest that adding non-Saccharomyces yeast during cold soak may be an effective method to reduce the production of volatile acidity by H. uvarum. Additional work is being conducted to test the effecacy of these cultures against other H. uvarum strains.

Funding Support: Oregon Wine Board