Vlatile Sulfur Cmpunds Winery Optins Wine/Enlgy-Grape Chemistry Grup Virginia Tech Bruce W. Zecklein Prfessr Emeritus Virginia Tech, Blacksburg, VA USA www.vtwines.inf
Vlatile Sulfur Cmpunds 4MMP: 4-mercapt-4-methylpentane-2- ne 3MH: 3-mercapthexan-1-l 3MHA: 3-mercapthexylacetate H 2 S Thils r mercaptans: R-S-H Disulfides: R-S-S-R Thiesters: R-S-CO-R
Off Odr Vlatile Sulfur Cmpunds Fruit arma / flavr Always changing, but still there Crrelates with ATA Wine/Enlgy-Grape Chemistry Grup Virginia Tech
Enlgy-Grape Chemistry Grup H 2 S Frmatin by Yeast During Fermentatin Virginia Tech Sulfur (S 0 ) Sulfate (SO 4-2 ) Sulfite (HSO -3 ) H 2 S Sulfide (S -2 ) Organic S Glutathine
Surce: Bell and Henschke 2005 Yeast Sulfate Reductin System
SLO Sensry Descriptin Sensry Threshld (μg/l) Biling Pint ( C) Hydrgen Sulfide Rtten egg 0.5-61 Carbnyl Sulfide Ether 3.0-50 Methyl Mercaptan, Methanethil Stagnant water 1.5 6 Ethyl Mercaptan, Ethanethil Onin 1.1 35 Dimethyl Sulfide Quince, truffle 10.0 35 Methinl Cked cabbage 1200 90 Diethyl Sulfide Ether 0.9 92 Dimethyl Disulfide Quince, asparagus 15.0 109 Diethyl Disulfide Garlic, rubber 4.3 151 Thiacetic Acid Esters Surce: Rauhut and Spnhlz 1992,
A HACCP plan: Steps t Manage SLO Factrs impacting yeast perfrmance Measure yeast assimilable nitrgen (YAN) Factrs impacting YAN Cntrl must turbidity Optimize xygen management Prper cncentratin and timing f nutrients Avid carbn dixide txicity Understand xidatin reductin ptential and SLO Understand pst-fermentatin and SLO www.vtwines.inf
Sensry/Physical Prperties f SLO H 2 S Thils r mercaptans: R-S-H Disulfides: R-S-S-R Thiesters: R-S-CO-R Prperties vary depending n cmpund, cncentratin, matrix (including ther VSC), xidatin-reductin ptential Thils (R-S-H) have much lwer sensry threshlds than Disulfides (R-S-S-R) Thils are easily xidized t Disulfides
ODOR SCREEN Glass 1 cntrl Glass 2 cpper Glass 3 cadmium Glass 4 ascrbic + Cu Types f reductive cmpunds) Odr gne Odr gne Odr gne H 2 S Off Odr gne N change Odr gne Mercaptan Odr Odr gne Slight imprvement Odr gne H 2 S and mercaptan N change N change Odr gne Disulfides N change N change N change Dimethyl sulfide Adapted frm Zecklein, et al. 1999, Available at www.vtwines,inf.
Crrective Actins Aeratin/Micrx/ Sparging Stirring Lees additin Cpper additin Prprietary prducts Wine/Enlgy-Grape Chemistry Grup Virginia Tech
Wine/Enlgy-Grape Chemistry Grup Remval f SLO Virginia Tech Splash racking- Always the crrect chice? What can happen? Precipitatin, Vlatilizatin, Oxidatin, Micrbial grwth and increased prductin Knw the SLO in the wine ppt: 2 H 2 S + O 2 2 H 2 O + S In the presence f sulfur dixide: SO2 + 2 H2S 2 H2O + 3 S
2 H 3 C SH methanethil sensry threshld 0.2 ppb xidatin reductin H 3 C S S CH 3 dimethyl disulfide sensry threshld 12 ppb 2 R-S-H + ½ O 2 R-S-S-H + H 2 O
Redx A series f interlinked reactins invlving the xidatin f ne cmpund and the reductin f anther As electrns are transferred, ne cmpund is xidized, while the ther reduced Electrns are rearranging themselves int a mre favrable rder
Redx Redx ptential can be measured in the same way that ph is measured, althugh it is slightly mre invlved Redx ptential is a measure f hw xidative r reductive a system is, measured in millivlts (mv) The higher the mv, the less reductive Aerated red wine: redx ptential 400-450 mv Nn-aerated stred red wine: 200-250 mv Redx ptential changes much mre easily in whites
QDA Wine Statin #4 (Napa Valley, Cabernet) Arma Descriptrs Fruit** 8.0 P = 0.026 Treated Cntrl Oxidatin 6.0 4.0 2.0 0.0 Veggy ** P = 0.013 Herbal Spicy Oak Surce: Zecklein et al., 2002
Wine/Enlgy-Grape Chemistry Grup Reactins with Cpper Virginia Tech H 2 S + CuSO 4 CuS + H 2 SO 4 2 CH 3 SH + ½ O 2 CH 3 SSCH 3 + H 2 O Methyl mercaptan dimethyl disulfide SO 2 Ascrbic Acid
Cpper a Strng Oxidizer H 2 O 2 + CU +2 > Cu +3 + OH - + OH* OH* r hydrxyl radical is the mst xidative species in wine Prblem in wines with a relatively lwer cncentratin f xidative buffers Prblem with late seasn Brdeaux mix Bnds with sme desirable VSC
cnc. (mg/l) Changes in H 2 S and Methanethil Cntent After Lees Cntact f 24 Hr. in Barrel 8 6 4 2 0 Day 1 Day 2 H 2 S MeSH Surce: Lavigne-Cruège and Duburdieu, 2001
cnc. (mg/l) Changes in H 2 S Cntent in Wine n Lees in Barrel 8 6 4 2 0 Day 2 Day 9 Day 12 Day 26 Surce: Lavigne-Cruege and Duburdieu, 2001
Thank Yu! Bruce Zecklein Enlgy-Grape Chemistry Grup Virginia Tech www.vtwines.inf