Effects of Inoculation Level During and After Fermentation

Student Team

Meredith Bell, Sarah Harper, Joanne Oh, Diego Roig and Luke Bohanan

Fermentation Analysis

Diego Roig

Goal of Study

• To compare the effect of different levels of inoculation of active dry commercial yeast preparations on fermentation and sensory characteristics of wine

• Used Chardonnay juice and Premiere cuvee

2010 UC Davis Chardonnay• Crushed and Pressed 9/2/10• Healdsberg crusher destemmer • Bucher Vaslin Press• Juice held in cold storage

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2010 UC Davis Chardonnay• Split into six, 10 gal drums• Inoculated 10/8/10• Premier cuvee• 6 inoculation levels

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Inoculation Levels

Lot 1 2 3 4 5 6

Yeast (g) 0g 0.008 0.25 8.0g 80.0g 140g

Cells/ml 0 103 104.5 106 107 1.8x107

Chemistry of Juice:Brix: 25.25; pH3.66; TA 4.98 (g/L)NOPA: 56; Ammonia:132; YAN: 188

Fermentation

• Cold fermentation cellar• Brix and Temp taken twice daily• When Dry, moved to cold storage

-5

0

5

10

15

20

25

30

°Bri

x

Hours after inoculation

Fermentation of 2010 Chardonnay

Sample 1 Temperature

Sample 1 °Brix

Sample 2 Temperature

Sample 2 °Brix

Sample 3 Temperature

Sample 3 °Brix

Sample 4 Temperature

Sample 4 °Brix

Sample 5 Temperature

Sample 5 °Brix

Sample 6 Temperature

Sample 6 °Brix

C

30

25

15

10

5

0

20

Rate of FermentationInoculation Level

• Inoculation size directly effects the rate of fermentation

• Larger initial biomass • Less time/energy spent on achieving

maximum cell density (2 x 108 cells/mL) despite lower maximum growth rate

Temperature• Temperature is important component of

any fermentation.• Premier cuvee yeast has temp. range of 7-

35°C• Chardonnay temps were b/w 12-18°C,

with no irregular heat spikes

Temperature• Highest temperatures throughout study seen in natural

fermentation despite slowest rate of fermentation• Max. temp. (natural fermentation): 17.9°C• Max. temp. (inoculated fermentations): 17.2-17.3°C

• Possible explanations• Heat generation during yeast budding• Different yeast strain dominating fermentation• Closer to warmer area of room (not likely)

Date Blend ID % EtOH pH TA (g/L) VA (g/L)

11/15 1 14.9 3.82 5.78 0.40

11/15 2 14.7 3.82 6.07 0.44

11/15 3 14.9 3.83 5.71 0.44

11/15 4 15.7 3.82 5.79 0.33

11/15 5 15.4 3.73 6.23 0.27

11/15 6 14.9 3.72 6.68 0.35

Lab Analysis of the Finished Wine

  1 2 3 4 5 6

10/29 2-3% 1-1.5%

1-1.5%

Trace Trace - Neg

Neg

11/5 2% 1% 0.5% Trace Neg Neg

11/12 Trace 0.5-1%

0.5-1%

Trace Neg Neg

Results of the Residual Sugar Testing

Chemical AnalysisEthanol Inhibition

• Inoculation levels shown to increase EtOH tolerance

• Current study confirms previous findings.• Slower rates of fermentation at lower inoculation

levels possibly due to decreased EtOH tolerance of yeast

Chemical AnalysisVolatile Acidity

• Lower VA measurements at higher inoculation levels

• Acetobacter repressed in absence of oxygen• Lower VA measurements correlated to shorter

lag phase?• Different strains of S. cerevisiae produce

varying amounts of acetic acid• May explain lower measurement in Lot 1

Chemical AnalysispH/Titratable Acidity

• Malolactic fermentation results in increase in pH and decrease in TA

• Slower fermentations saw pH increase and decrease in TA

• Possible that ML fermentation began?• Colder temps inhibit ML, Lots 5/6 moved to cold

room 2 weeks sooner than rest of Lots

Sensory Analysis

Luke Bohanan

Sensory Evaluation

• Acceptance test with hedonic scale• Aroma only• 2 Repetitions all wines• Randomly numbered• Randomly ordered• Judge tracking

Mean Preference Scores

0 1 2 3 4 5 6 70.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

Series1

• Reasonable Variance• Two Distinct groups• Outliers…

ANOVA

• XLSTAT used • Judges H0 rejected = Not all Judges scored the same

• Wines H0 rejected = Not all wines were scored the same

• Reps H0 accepted = No significant difference between reps

Judge Grouping From LS Mean

3.000 3.250 3.500 3.750 4.000 4.250 4.500 4.750 5.000 5.250 5.500 5.750 6.000 6.250

J3J7J4J10

J6J12J13J5J14

J9J8J1J2J9

Series1D C B A

Wine Grouping from LS Mean

1.500 2.000 2.500 3.000 3.500 4.000 4.500 5.000 5.500 6.000 6.500 7.000

W4W2

W1W3W5W6

Series1

C B A

Preference Mapping

W1W2

W3 W4W5W6

J1J2J3J4J5J6J7

J8J9J10J11J12J13J14

-200

-150

-100

-50

0

50

100

150

-250 -200 -150 -100 -50 0 50 100 150 200

F2 (0

.00

%)

F1 (100.00 %)

Biplot (axes F1 and F2: 100.00 %)

• Judges in tight group compared to wines• Drastic difference in wine grouping

Mean Factor Score from PCA

-15

-10

-5

0

5

10

1 2 3 4 5 6

Mean Factor Score by Wine Treatment

Mean Factor Score

• Wines 5 and 6 are disliked • Wines 1-4 are liked• Wine 4 is liked the most

What does sensory tell us?

• Highest concentration of desired aroma compounds at 106 cells/ml

• Higher concentration of undesirable compounds at 107 cell/ml and above

• Concentrations below 106 cells/ml show acceptable levels of desirable aromas

Possible causes of negative aromas

• Treatment 5 and 6 left on mass of lees = reductive environment = sulfur

• Lack of nutrients• Post fermentation contamination• Headspace post fermentation = O2 Exposure

Questions?