1a.Objectives (from AD-416):
Evaluate methods of detection for Zygosaccharomyces; Determine the impact of selected strains of Zygosaccharomyces on wine composition and quality.
1b.Approach (from AD-416):
Strains will be grown on non-selective media for routine maintenance and preparation of starter cultures for wine inoculation. Modification and optimization of alternative selective media will focus on (a) substitution of carbon sources and (b) lowering the water activity of the medium. Selected strains of Zygosaccharomyces will be inoculated small scale. During incubation, general analyses to be performed include culturability (plate count), volatile acidity (Cash still), and, if applicable, rate of fermentation (soluble solids). For those strains were no obvious sensory differences exist between wines without or with inoculation of Zygosaccharomyces, vinification experiments of a larger scale will be conducted with additional chemical and sensory analyses.
This research was conducted in support of NP 305 objective 1 "Determine nutrient requirements to enhance product quality in woody perennial crops such as grapevine and rhododendron" of the parent project. An alternative approach to remove residual sugar from partially-fermented wines using Zygosaccharomyces was studied. To simulate stuck fermentations, dry red wines were adjusted to 13, 15, or 17% v/v ethanol and 40 or 60 g/L fructose prior to inoculation with Zygosaccharomyces bailii (strains W3, ZB2, or ZB6) or Saccharomyces cerevisiae (strain EC1118) at ˜108 cfu/mL. Most strains maintained culturable populations =106 cfu/mL, the exceptions being W3 and EC1118 which declined to undetectable levels past day 75 in 17% ethanol wines. However, these same strains consumed >90% of the 40 g/L or 33% of the 60 g/L fructose present in the 15% ethanol wines. None of the wines with greater ethanol concentrations inoculated with Z. bailii reached dryness (<2 g/L), although only 3 g/L fructose remained in 15% ethanol wines initially containing 40g/L fructose with strain W3. Few differences in sugar utilization were noted in wines containing 17% ethanol where metabolic activities ceased with approximately 50% of the original amount of fructose present. While Z. bailii metabolized some residual fructose in wines of varying alcohol content, the use of S. cerevisiae was generally more effective and did not produce as much volatile acidity.