Fermentation Performance of Four Saccharomyces cerevisiae Yeast Strains in Difficult to Ferment Chardonnay Juice

Despite efforts to optimize the conditions of fermentation, some wineries still encounter fruit that is perennially difficult to ferment. This study focuses on a Chardonnay with a history of long, sluggish fermentation. The goal of this research was to screen a large collection of yeasts to identify strains that are capable of efficient fermentation of this juice. Two native isolates and two sequenced strains were chosen for full evaluation from a screening of 14 strains. These strains were evaluated in 6-replicate trials, and a metabolomic analysis was conducted at day 4. A Chardonnay juice with no history of fermentation issues from the same producer was used for comparison. Strain UCD2778 fermented to dryness in both juices, but fermentation rate in the difficult juice exceeded the easy juice at 72 hrs, and cumulative weight loss was greater in difficult juice thereafter. Difficult juice viability was nominally but not significantly lower. Strain UCD2780 had a higher fermentation rate in difficult juice at 72 hours. Strains UCD2176 and UCD2780 exhibited greater cumulative weight loss in the difficult juice than in the easy juice. Strain UCD2176 fermentation arrested at 8-9 Brix, with easy juice fermenting further than difficult juice by about one degree. For strains UCD2780 and UCD2176, cell viability dropped more quickly in difficult juice than in easy juice during fermentation. Strain UCD2118 was the only strain that did not show a juice-based difference in fermentation performance. This strain also flocculated upon completing fermentation in four of the six difficult juice replicates. Metabolomics analysis on day four of fermentation indicated that strain UCD2176 was generally distinct from the other strains in both difficult and easy Chardonnay. Strain UCD2118 was distinct from strains UCD2780 and UCD2778 in difficult juice only, suggesting that it made adaptive changes to the metabolome in response to its environment. Several of the metabolites that distinguished strains UCD2118 and UCD2176 from other strains are related to stress responses and membrane synthesis, such as trehalose, mannitol, proline, myo-inositol, and ethanolamine. These findings offer insight into how strain UCD2118 was metabolically prepared to succeed in the difficult juice, and whether flocculation was an advantage in this environment.