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

inoculationSaccharomyces from vineyard: 1-2 cells/1000

mLSaccharomyces 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

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

What limits cell growth?

Availability of nutrients Presence of non-permissive conditions

TemperatureEthanolCompetitionInhibitors

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 nutrientsLess need to produce new cellsHigher 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