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