Wine yeasts vary quite dramatically in their efficiency in converting grape juice nutrients into active biomass. Wine yeast strains that are grown in the same medium or juice will reach different maximum cell concentrations. In general, strains that reach a greater cell concentration will have fewer problems completing fermentations. We have taken a multifaceted approach to understanding the metabolic and regulatory differences among yeast strains that cause these differences in nutrient utilization efficiency (NUE). Initially, we focused on four commercial wine yeast strains with varying NUE, Montrachet, Cote des Blanc, T306, and Uvaferm 43, using small scale (400 mL) fermentations in synthetic MMM medium. The maximum cell concentration reached by these strains ranged from an OD_{600 nm} of 5.3 to 7.9. We analyzed the intracellular and extracellular metabolites during fermentation using GC-MS and HPLC-RI, respectively. Complete analysis of the lipid profile of each strain was performed using Triple Quadrupole LC-MS. In addition, we used a transcriptomic approach (RNA-Seq) to understand relevant transcriptional control mechanisms. Using principal pomponent analysis with initial metabolomic data, we observed that certain key metabolic pathways are most relevant in determining NUE, including the pentose-phosphate pathway, TCA cycle, and fatty acid synthesis. To further confirm our results, we used a series of wine yeast mutants that overexpress key pathway enzymes.

Funding Support: American Vineyard Foundation, Ernest Gallo Endowed Chair in Viticulture and Enology