Effect of low temperature on the shaping of yeast-derived metabolite compositions during wine fermentation.

Low-temperature fermentation is considered to enrich the aroma of wine. The metabolism of Saccharomyces cerevisiae responding to low temperatures is intricate and this complexity is further enhanced by various strains and culture media. However, the real effects of low-temperature fermentation on yeast metabolism are unclear. Aiming to clarify the yeast-derived metabolite formation in a low-temperature winemaking range, fermentations were performed at 10, 15, and 20 °C, using five wine yeast strains in two media respectively. Tolerance toward low temperatures and metabolite compositions (including basic chemical compositions and volatile aroma compounds) of wine yeasts were analyzed. Results showed that ethanol, ethyl acetate, and ethyl butanoate increased with the temperature decreasing, while acetic acid, phenylethanol, phenylethyl acetate, ethyl decanoate, and ethyl hexadecanoate decreased with decreasing temperature. The linear relationship between fermentation temperature and the formation of ethanol, acetic acid, and phenylethanol might be fundamentally due to the growth changes caused by temperature. The enhanced production of ethyl acetate and ethyl butyrate followed by decreasing temperature probably resulted from low-temperature-stimulated enzymes in metabolic pathways. These findings reveal a typical profile of yeast-derived metabolites at low-temperature fermentation and provide evidence to support the application of low-temperature winemaking in the wine industry.

Yeast Diversity during Spontaneous Fermentations and Oenological Characterisation of Indigenous Saccharomyces cerevisiae for Potential as Wine Starter Cultures.

Diversity of regional yeast can be influenced by geography, grape cultivars and the use of SO2, but at single vineyard scale in China, the impact of these factors on yeast population, particularly Saccharomyces cerevisiae, is not well studied. Here, we characterised yeast species and dynamics during spontaneous fermentations with/without SO2 using eight typical grape cultivars from Yuma vineyard in Ningxia wine region of China. Results show that distribution and abundance of yeast species varied by grape varieties, fermentation stage and SO2 treatment. A number of 290 S. cerevisiae isolates were further classified into 33 genotypes by Interdelta fingerprinting. A prevailing role of grape varieties in shaping the genetic divergence of S. cerevisiae in Yuma vineyard was observed, as compared to the impacts of fermentation stage and SO2 treatment. Pre-selected S. cerevisiae strains were subjected to vinification with Cabernet Sauvignon and Chardonnay. All strains completed fermentations but the physiochemical parameters and volatile profiles of wines were strain-specific. Some indigenous S. cerevisiae yielded more desirable aroma compounds compared to the commercial strains, among which NX16 and NX18 outcompeted others, therefore having potential for use as starters. This study provides comprehensive analysis on yeast diversity at vineyard scale in Ningxia. Information on the vinification using indigenous S. cerevisiae is of great value for improving Ningxia wine regionality.