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  Can impact ethanol yield

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

Level of Inoculation  Native fermentation: no deliberate inoculation  Saccharomyces from vineyard: 1-2 cells/1000 mL  Saccharomyces from winery: 10 2 – 10 4 cells/mL  Typical inoculation level: lbs/1000 gallon (10-30 g/hL) or 1-2% of an active fermentation  Approximately 1-3 x10 6 cells/mL

Cell Growth  Cells grow until reaching a terminal cell density  Cells attain 2 x 10 7 to 1 x 10 8 cells/mL during fermentation  Starting at 10 6 cells/mL means cells will undergo 4 to 7 generations before reaching terminal cell density

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

Impact of Level of Inoculation  Higher levels of inoculation  Lower levels of inoculation

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:

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

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