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Volatile Sulfur Compounds Winery Optionsppt: 2 H 2 S + O 2 2 H 2 O + S ... Bonds with some desirable...
Transcript of Volatile Sulfur Compounds Winery Optionsppt: 2 H 2 S + O 2 2 H 2 O + S ... Bonds with some desirable...
Volatile Sulfur Compounds
Winery Options
Virginia Tech
Wine/Enology-Grape Chemistry Group
Bruce W. ZoeckleinProfessor Emeritus
Virginia Tech, Blacksburg, VA USA
www.vtwines.info
Volatile Sulfur Compounds
H2S
Thiols or mercaptans: R-S-H
Disulfides: R-S-S-R
Thioesters: R-S-CO-R
4MMP: 4-mercapto-4-methylpentane-2-
one
3MH: 3-mercaptohexan-1-ol
3MHA: 3-mercaptohexylacetate
Off Odor Volatile Sulfur Compounds
• Fruit aroma / flavor
• Always changing, but still there
• Correlates with ATA
Virginia Tech
Wine/Enology-Grape Chemistry Group
H2S Formation by Yeast
During Fermentation
Sulfur (S0)
Sulfate (SO4-2)
Sulfite (HSO-3)
H2S
Sulfide (S-2)
Organic – S
Glutathione
Virginia Tech
Enology-Grape Chemistry Group
Yeast Sulfate Reduction System
Source: Bell and Henschke 2005
SLOSensory
Description
Sensory
Threshold
(μg/L)
Boiling
Point
( C)
Hydrogen Sulfide Rotten egg 0.5 -61
Carbonyl Sulfide Ether 3.0 -50
Methyl Mercaptan,
Methanethiol
Stagnant
water1.5 6
Ethyl Mercaptan,
EthanethiolOnion 1.1 35
Dimethyl Sulfide Quince, truffle 10.0 35
Methionol Cooked cabbage 1200 90
Diethyl Sulfide Ether 0.9 92
Dimethyl DisulfideQuince,
asparagus15.0 109
Diethyl Disulfide Garlic, rubber 4.3 151
Thioacetic Acid Esters Source: Rauhut and Sponhlz 1992,
Steps to Manage SLO
A HACCP plan:
o Factors impacting yeast performance
o Measure yeast assimilable nitrogen (YAN)
o Factors impacting YAN
o Control must turbidity
o Optimize oxygen management
o Proper concentration and timing of nutrients
o Avoid carbon dioxide toxicity
o Understand oxidation reduction potential and SLO
o Understand post-fermentation and SLO
www.vtwines.info
Sensory/Physical Properties of SLO
H2S
Thiols or mercaptans: R-S-H
Disulfides: R-S-S-R
Thioesters: R-S-CO-R
o Properties vary depending on compound, concentration,
matrix (including other VSC), oxidation-reduction potential
o Thiols (R-S-H) have much lower sensory thresholds than
Disulfides (R-S-S-R)
o Thiols are easily oxidized to Disulfides
Glass 1
control
Glass 2
copper
Glass 3
cadmium
Glass 4
ascorbic + Cu
Types of
reductive
compounds)
Odor gone Odor gone Odor gone H2S
Off Odor gone No change Odor gone Mercaptan
Odor Odor gone Slight
improvement
Odor gone H2S and
mercaptan
No change No change Odor gone Disulfides
No change No change No change Dimethyl
sulfide
Adapted from Zoecklein, et al. 1999, Available at www.vtwines,info.
ODOR SCREEN
Corrective Actions
• Aeration/Microx/ Sparging
• Stirring
• Lees addition
• Copper addition
• Proprietary products
Virginia Tech
Wine/Enology-Grape Chemistry Group
Removal of SLO
Splash racking-
Always the correct choice?
What can happen?
Precipitation, Volatilization, Oxidation, Microbial growth
and increased production
Know the SLO in the wine
ppt: 2 H2S + O2 2 H2O + S
In the presence of sulfur dioxide: SO2 + 2 H2S 2 H2O + 3 S
Virginia Tech
Wine/Enology-Grape Chemistry Group
2H3C
SH
H3C
S
S
CH3oxidation
methanethiol
sensory threshold 0.2 ppb
dimethyl disulfide
sensory threshold 12 ppb
reduction
2 R-S-H + ½ O2 R-S-S-H +
H2O
Redox
A series of interlinked reactions
involving the oxidation of one compound
and the reduction of another
As electrons are transferred, one
compound is oxidized, while the other
reduced
Electrons are rearranging themselves
into a more favorable order
Redox
Redox potential can be measured in the same way that
pH is measured, although it is
slightly more involved
Redox potential is a measure of how oxidative
or reductive a system is, measured in millivolts (mV)
The higher the mV, the less reductive
Aerated red wine: redox potential 400-450 mV
Non-aerated stored red wine: 200-250 mV
Redox potential changes much more easily in whites
QDA Wine Station #4 (Napa Valley, Cabernet)
Aroma Descriptors
P = 0.026
P = 0.013
0.0
2.0
4.0
6.0
8.0
Fruit**
Veggy **
Spicy
Oak
Herbal
Oxidation
Treated
Control
Source: Zoecklein et al., 2002
Reactions with Copper
•H2S + CuSO4 CuS + H2SO4
• 2 CH3SH + ½ O2 CH3SSCH3 + H2O
Methyl mercaptan dimethyl disulfide
SO2
Ascorbic Acid
Virginia Tech
Wine/Enology-Grape Chemistry Group
Copper – a Strong Oxidizer
H2O2 + CU+2 > Cu+3 + OH- + OH*
OH* or hydroxyl radical is the most oxidative species in wine
Problem in wines with a relatively lower
concentration of oxidative buffers
Problem with late season Bordeaux mix
Bonds with some desirable VSC
Changes in H2S and Methanethiol Content
After Lees Contact of 24 Hr. in Barrel
H2S
MeSH
Day 1 Day 2
con
c. (
mg
/L)
0
2
4
6
8
Source: Lavigne-Cruège and Dubourdieu, 2001
Changes in H2S Content in Wine on Lees
in Barrel
con
c. (
mg
/L)
0
2
4
6
8
Day 2 Day 9 Day 12 Day 26
Source: Lavigne-Cruege and Dubourdieu, 2001
Thank You !
Bruce ZoeckleinEnology-Grape Chemistry Group
Virginia Tech
www.vtwines.info