Impact of Vineyard Residues on Wine Quality Linda

Impact of Vineyard Residues on Wine Quality Linda F. Bisson Department of Viticulture and Enology University of California, Davis

Types of Vineyard Residues n Fungicide treatments n Pesticides n Foliar sprays

Possible Impacts of Vineyard Residues n Primary Impacts: – Inhibition of yeast fermentation – Inhibition of malolactic conversion – Off-character formation § Direct § Due to yeast metabolism § Due to bacterial metabolism n Secondary Impacts: – Alteration of berry microbiota

Common Impacts on Wine Aroma n n n Direct detection of residue: rare S 0 or S-containing compounds: S-volatile formation Antifungal agents: can impact fermentation aroma in addition to fermentation progression Antibacterial agents: can impact fermentation aroma in addition to MLF progression Sometimes the impact is a depression of aroma

Why Is There an Impact on Aroma? n Microbes must detoxify component n Component may simply be metabolizable by microbial enzymes n May inhibit a primary pathway forcing a secondary pathway to be used instead n May simply be altered chemically due to the reductive conditions established by yeast metabolism

Is There a Problem with Vineyard Residues? n Generally all products should have been tested thoroughly for impacts on microbes and wine aroma n Timing of use can prevent any residuals from entering the winery n More growers are adopting organic and sustainable practices

Elemental Sulfur n Used to control mildew n No resistances have been developed n Is a natural fungicide (not synthetic) n Residues can pose a problem: – High levels inhibitory to yeast – Low levels lead to H 2 S formation

Elemental Sulfur Residues n Depends upon how S 0 was applied n Depends upon timing of application versus harvest date n References: – Thomas, CS, et al (1993) AJEV 44: 205 (residue levels with different S 0 formulations) – Thomas, CA et al (1993) AJEV 44: 211 (impact of S 0 spikes on H 2 S formation)

Hydrogen Sulfide (H 2 S) in Winemaking n Hydrogen sulfide production by Saccharomyces occurs as a part of yeast metabolism during fermentation. n Rotten egg character n Range of production is 0 – 300 μg/L. n Threshold of human odor detection is 0. 11 μg/L in wine. n Varies by genetic background of yeast

H 2 S is Formed in Three Ways during Wine Fermentation Sulfur MET/CYS Sulfate Chemical conversion pathway in yeast H 2 S Sulfate reduction Sulfide H 2 S in Wine

Elemental Sulfur and H 2 S n Several studies suggest H 2 S increases with increasing S 0 – Not strain dependent – Due to reductive environmental conditions n Strain effects dominate that of S 0 addition n Beliefs: – S 0 residues converted to H 2 S during fermentation – Nitrogen addition does not prevent H 2 S formation from S 0

Problems with Research to Date n Yeast strains make H 2 S from sulfate reduction and other sources: high background levels n Yeast strain sulfide levels often exceed those of S 0 n Not all of the S 0 can be accounted for as H 2 S

Research Approach n Take yeast advantage of MET 10 -932 (H 2 S-less) n MET 10 -932 allele: – Yeast do not make H 2 S – Can change just this one gene and compare impact of increasing S 0 levels – Can assess wine for the appearance of other off-odors or traits that are associated with S 0

Goals n Evaluate the impact of elemental sulfur addition on H 2 S production by using strains with differing abilities to reduce sulfate to sulfide n Can yeasts still produce H 2 S from elemental sulfur when sulfite reductase is not functional? n How much impact?

Genotypes and Phenotypes of Modified Yeast Strains UCD 522 (wild type) n UCD 932 (wild type) n S 288 C (wild type) n n n 522Δmet 10 522 MET 10932 522 MET 10522 522 MET 10 S 288 C H 2 S Production + +

Growth on Selective Medium YPD YNB UCD 522 UCD 932 522 MET 10522 522Δmet 10 522 MET 10932 Bi. GGY media 522 MET 10 S 288 C H 2 S Producers / H 2 S Producers

Fermentation Media Synthetic grape juice (Minimal Must Media) 433, 208, 123 mg/L of nitrogen 20 mg/L of methionine n Chardonnay juice (’ 08 Woodbridge, filtered, 23. 5 Brix) 450. 3 mg/L of nitrogen 12. 02 mg/L of methionine n Directly spiked with elemental sulfur (Thiosperse) 0, 1. 7, 3. 4, 6. 8 mg/L of sulfur n

Fermentation Conditions n n n 150 m. L media / 250 m. L flask Silicon stopper FIGASA® H 2 S detecting tube 25°C, 120 rpm Until reach dryness (<0. 25% sugar) Triplicates 250

H 2 S Measurement on Tube n Blackened length in mm on scaled lead acetate tube n 1 mm equals to 1. 2 µg of H 2 S

H 2 S Production in 433 mg/L N

H 2 S Production in 208 mg/L N

H 2 S Production in 123 mg/L N

H 2 S Production in Chardonnay

Conclusions From This Study n High S 0 does lead to increased H 2 S n Production of H 2 S both de novo and from S 0 depended upon the allele at MET 10 n Production of H 2 S both de novo and from S 0 depended upon nitrogen level – Moderate N gave highest levels of H 2 S with and without S 0 – Impact of S 0 more pronounced at high N levels

H 2 S Production in Red Wine with S 0 Spikes n Assess impact of S 0 residues in presence and absence of ability to make H 2 S n Evaluate changes in wine during aging

The Experiment for Today’s Wines 2010 UC Davis Grenache noir The Students: Constantin Heitkamp Shaunt Oungoulian Alex Stauffer Aaron Whitlatch

Experimental Design Crush / Destem 50 Gal TJs Additions/Inoc Pumpover 10 min per 12 hr Monitor Brix/Temp/Odor Press and Return to TJ Racked to Barrel Cold Storage Bottling Sensory Evaluation

Elemental Sulfur Spiking n Elemental Sulfur was added to juices prior to inoculation and mixed in n Sulfur residue levels were: O, 2, 4 mg/L Thiolux n Two yeast strains: Montrachet (UCD 522) and P 1 Y 0 -2 (Phyterra H 2 S-less yeast)

Montrachet Fermentation

P 1 Y 0 -2 Fermentation

Wine Sensory Analysis Hedonic Ranking December 2010 • P 0 > M 0, M 2, M 4 • P 2, P 4 > M 0, M 2 Indicates a clear preference to Phyterra Yeast • M 4 > M 0, M 2 Higher elemental sulfur did not lead to a decrease in aroma preference • All > M 2 During fermentation M 2 and M 4 had the greatest sulfur aroma, but M 4 did not score as poorly as M 2 when assessing the wine

Difference Testing Triangle Test • P 0 > M 0 • M 0 > M 2 • M 0 > M 4 This reaffirms the hedonic test ranking that Phyterra yeast is different from Montrachet The triangle test supports the hypothesis that increased elemental sulfur added to the fermentation leads to less preference in the wine (assumed to be sulfur aroma defect)

Conclusions n Phyterra yeast preferred immediately post fermentation: wines described as fresher and fruitier n M 2 fermentation was considered to be the least preferred and most defective in aroma n Impact of aging?

Acknowledgements n American Vineyard Foundation n California Competitive Grant Program for Research in Viticulture and Enology n Maynard A. Amerine Endowment

Sulfur Residues Flight n Glass 1: Montrachet, 0 ug/L S 0 n Glass 2: Montrachet, 2 mg/L S 0 n Glass 3: Montrachet, 4 mg/L S 0 n Glass 4: P 1 Y 0 -2, 0 ug/L S 0 n Glass 5: P 1 Y 0 -2, 2 mg/L S 0 n Glass 6: P 1 Y 0 -2, 4 mg/L S 0