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Impact of Vineyard Residues on Wine Quality

Impact of Vineyard Residues on Wine Quality. Linda F. Bisson Department of Viticulture and Enology University of California, Davis. Types of Vineyard Residues. Fungicide treatments Pesticides Foliar sprays. Possible Impacts of Vineyard Residues. Primary Impacts:

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Impact of Vineyard Residues on Wine Quality

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

  2. Types of Vineyard Residues • Fungicide treatments • Pesticides • Foliar sprays

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

  4. Common Impacts on Wine Aroma • Direct detection of residue: rare • S0 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

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

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

  7. Elemental Sulfur • Used to control mildew • No resistances have been developed • Is a natural fungicide (not synthetic) • Residues can pose a problem: • High levels inhibitory to yeast • Low levels lead to H2S formation

  8. Elemental Sulfur Residues • Depends upon how S0 was applied • Depends upon timing of application versus harvest date • References: • Thomas, CS, et al (1993) AJEV 44:205 (residue levels with different S0 formulations) • Thomas, CA et al (1993) AJEV 44:211 (impact of S0 spikes on H2S formation)

  9. Hydrogen Sulfide(H2S) in Winemaking • Hydrogen sulfide production by Saccharomyces occurs as a part of yeast metabolism during fermentation. • Rotten egg character • Range of production is 0 – 300 μg/L. • Threshold of human odor detection is 0.1-1 μg/L in wine. • Varies by genetic background of yeast

  10. H2S is Formed in Three Ways during Wine Fermentation Sulfur MET/CYS Sulfate Chemical conversionSulfate reduction pathway in yeast H2SSulfide H2S in Wine

  11. Elemental Sulfur and H2S • Several studies suggest H2S increases with increasing S0 • Not strain dependent • Due to reductive environmental conditions • Strain effects dominate that of S0 addition • Beliefs: • S0 residues converted to H2S during fermentation • Nitrogen addition does not prevent H2S formation from S0

  12. Problems with Research to Date • Yeast strains make H2S from sulfate reduction and other sources: high background levels • Yeast strain sulfide levels often exceed those of S0 • Not all of the S0 can be accounted for as H2S

  13. Research Approach • Take advantage of MET10-932 (H2S-less) yeast • MET10-932 allele: • Yeast do not make H2S • Can change just this one gene and compare impact of increasing S0 levels • Can assess wine for the appearance of other off-odors or traits that are associated with S0

  14. Goals • Evaluate the impact of elemental sulfur addition on H2S production by using strains with differing abilities to reduce sulfate to sulfide • Can yeasts still produce H2S from elemental sulfur when sulfite reductase is not functional? • How much impact?

  15. Genotypes and Phenotypes of Modified Yeast Strains H2S Production • UCD522 (wild type) • UCD932 (wild type) • S288C (wild type) • 522Δmet10 • 522MET10932 • 522MET10522 • 522MET10S288C + - + - - + +

  16. Growth on Selective Medium YNB YPD UCD522 UCD932 522MET10522522Δmet10 522MET10932 522MET10S288C BiGGY media H2S Producers / H2S Producers

  17. Fermentation Media • Synthetic grape juice (Minimal Must Media) 433, 208, 123 mg/L of nitrogen 20 mg/L of methionine • Chardonnay juice (’08 Woodbridge, filtered, 23.5 Brix) 450.3 mg/L of nitrogen 12.02 mg/L of methionine • Directly spiked with elemental sulfur (Thiosperse) 0, 1.7, 3.4, 6.8 mg/L of sulfur

  18. 150mL media / 250mL flask Silicon stopper FIGASA® H2S detecting tube 25°C, 120 rpm Until reach dryness (<0.25% sugar) Triplicates Fermentation Conditions 250

  19. H2S Measurement on Tube • Blackened length in mm on scaled lead acetate tube • 1 mm equals to 1.2 µg of H2S

  20. H2S Production in 433 mg/L N

  21. H2S Production in 208 mg/L N

  22. H2S Production in 123 mg/L N

  23. H2S Production in Chardonnay

  24. Conclusions From This Study • High S0 does lead to increased H2S • Production of H2S both de novo and from S0 depended upon the allele at MET10 • Production of H2S both de novo and from S0 depended upon nitrogen level • Moderate N gave highest levels of H2S with and without S0 • Impact of S0 more pronounced at high N levels

  25. H2S Production in Red Wine with S0 Spikes • Assess impact of S0 residues in presence and absence of ability to make H2S • Evaluate changes in wine during aging

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

  27. 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

  28. Elemental Sulfur Spiking • Elemental Sulfur was added to juices prior to inoculation and mixed in • Sulfur residue levels were: O, 2, 4 mg/L Thiolux • Two yeast strains: Montrachet (UCD522) and P1Y0-2 (Phyterra H2S-less yeast)

  29. Montrachet Fermentation

  30. P1Y0-2 Fermentation

  31. Wine Sensory Analysis • Hedonic Ranking - December 2010 • P0 > M0, M2, M4 • P2, P4 > M0, M2 • M4 > M0, M2 • All > M2 Indicates a clear preference to Phyterra Yeast Higher elemental sulfur did not lead to a decrease in aroma preference During fermentation M2 and M4 had the greatest sulfur aroma, but M4 did not score as poorly as M2 when assessing the wine

  32. Difference Testing • Triangle Test • P0 > M0 • M0 > M2 • M0 > M4 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)

  33. Conclusions • Phyterra yeast preferred immediately post fermentation: wines described as fresher and fruitier • M2 fermentation was considered to be the least preferred and most defective in aroma • Impact of aging?

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

  35. Sulfur Residues Flight • Glass 1: Montrachet, 0 ug/L S0 • Glass 2: Montrachet, 2 mg/L S0 • Glass 3: Montrachet, 4 mg/L S0 • Glass 4: P1Y0-2, 0 ug/L S0 • Glass 5: P1Y0-2, 2 mg/L S0 • Glass 6: P1Y0-2, 4 mg/L S0

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