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Impact of Level of Inoculation on Yeast Taints

Impact of Level of Inoculation on Yeast Taints. Linda Bisson Department of Viticulture and Enology UCD. Level of Inoculation. Impacts length of fermentation lag Impacts speed of domination of fermentation Affects aroma profile Affects mouth feel Can affect ethanol tolerance

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Impact of Level of Inoculation on Yeast Taints

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  1. Impact of Level of Inoculation on Yeast Taints Linda Bisson Department of Viticulture and Enology UCD

  2. Level of Inoculation • Impacts length of fermentation lag • Impacts speed of domination of fermentation • Affects aroma profile • Affects mouth feel • Can affect ethanol tolerance • Can impact ethanol yield

  3. Research Studies Show: • The higher the inoculum level the more rapid the decrease in non-Saccharomyces yeasts • At higher yeast dosage levels the specific growth rate is decreased: more competition for nutrients • Greater ethanol tolerance at higher dosage levels: stress tolerance factors induced early • Lower inoculation levels result in higher ethyl ester formation and decreased acetate ester and fusel oil formation

  4. Level of Inoculation • Native fermentation: no deliberate inoculation • Saccharomyces from vineyard: 1-2 cells/1000 mL • Saccharomyces from winery: 102 – 104 cells/mL • Typical inoculation level: 1-2.5 lbs/1000 gallon (10-30 g/hL) or 1-2% of an active fermentation • Approximately 1-3 x106 cells/mL

  5. Cell Growth • Cells grow until reaching a terminal cell density • Cells attain 2 x 107 to 1 x 108 cells/mL during fermentation • Starting at 106 cells/mL means cells will undergo 4 to 7 generations before reaching terminal cell density

  6. What limits cell growth? • Availability of nutrients • Presence of non-permissive conditions • Temperature • Ethanol • Competition • Inhibitors • Presence of high cell density (may count non-growing cells that are still metabolically active

  7. Impact of Level of Inoculation • Higher levels of inoculation • Lower levels of inoculation

  8. Impact of Level of Inoculation • Higher levels of inoculation: • More rapid domination of fermentation: reduced influence of non-Saccharomyces organisms • Enhanced consumption of nutrients • Less need to produce new cells • Higher ethanol concentrations • Lower levels of inoculation:

  9. Impact of Level of Inoculation • Higher levels of inoculation: • Lower levels of inoculation: • More time required to dominate fermentation: greater contribution from non-Saccharomyces yeasts • Need to make more cell biomass, reducing ethanol yield (but only by 0.5-1%) • Populations better adapted to increasing ethanol concentrations

  10. If level is too high . . . • Quorum (density) signaling molecules made early and in higher concentration: non-fruity esters, fusel oils and S-compounds • Fermentation is conducted “on lees” rather than by actively growing cells: more reduced character • Get more stress characters: fusel oils • Oxygen consumed rapidly and not enough available for cell population: more reduced character

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