VWT 272 Class 7

Quiz 5

Number of quizzes taken 19

Min 2

Max 30

Mean 19.5

Median 23

Mode 24

Lecture 7 Other (Smelly) Sulfur Compounds

He that lives upon hope will die farting. Benjamin Franklin (1706-1790)

Plan of Study • Review The “Sulfur Dioxide Family”

– Sulfite Bisulfite Molecular SO2

– Free vs. Bound vs. Total

– SO2 additions

• Vineyard Sulfur Additions – S vs. Bordeaux Mixture

• Hydrogen Sulfide – Causes

• Vineyard S, yeast nutrition, or ???

– Prevention

– Removal • CuSO4 vs. wishing

• Disulfide

The (SO2) Family Equilibrium

Sulfite Bisulfite Molecular SO2

SO32- HSO3

- SO2 (aq)

• The concentration of each family member depends upon pH

Sulfite ion (SO32-)

• At wine pH is virtually nonexistent

– 1 to 3 μM

– < 0.01% at pH 3.4

• Is a good Antioxidant (O2 grabber)

– BUT requires much higher pH

Bisulfite ion (HSO3-)

• At wine pH is Most common form – 94.4% at pH 3.0 – 99.4% at pH 4.0

• Is not a good Antioxidant (O2 grabber)

• Is not a good Antimicrobial • Binds with the carbonyl oxygen in

– Acetaldehyde – Glucose – Keto acids

• Pyruvate

• Inhibits polyphenol oxidase

Acetaldehyde • Produced by Saccharomyces cerevisiae

– Then Re-utilized by the yeast

• Malolactic bacteria degrade Acetaldehyde during MLF

• Oxidation

– “Coupled” chemical reaction

• O2 reacts with a phenol to make Quinone + Hydrogen Peroxide (H2O2)

• Hydrogen Peroxide oxidizes Ethanol to Acetaldehyde

Bisulfite ion (HSO3-)

• Binds with the carbonyl oxygen in Acetaldehyde

• Binds with other carbonyl group containing molecules to form “Bound SO2”

Molecular SO2 • At wine pH is present in small amounts

– 5.6% at pH 3.0

– 0.6% at pH 4.0

• Is responsible for antimicrobial action – Not ionic – can pass through cell membranes

– Disrupt enzyme activity

– Disturb protein structure

• Reacts with Hydrogen Peroxide (H2O2) to make Sulphate SO4

2- before it can react with ethanol SO2 + H2O2 → 2H+ + SO4

2- “Fast”

CH3CH2OH + H2O2 → CH3CHO + 2 H2O “Slow”

Molecular SO2 The Table

Free vs. Bound SO2

• At wine pH

– Bound (BSO2) is all SO2 in the Bisulfite ion (HSO3-)

form that is bound to

• Acetaldehyde

• Glucose

• Keto Acids

– Free (FSO2) is all SO2 in the Bisulfite ion (HSO3-)

form that is NOT bound + all Molecular SO2

– Total SO2 (TSO2) = FSO2 + BSO2

Free SO2 Addition Calculations

• Imprecise “GUIDE” for SO2 Addition in Juice/Must

– Assume ~ 60 % of your added SO2 will be bound (BSO2)

• 100 mg added SO2/40 mg free SO2

• Concentration will drop rapidly to unmeasurable

– Damaged fruit will require significantly more SO2

Free SO2 Addition Calculations

• Imprecise “GUIDE” for SO2 Addition in Wine – ~ 50% of SO2 Addition becomes quickly bound in

young wines and wines below 60 mg/L TSO2

• 100 mg added SO2/ 50 mg free SO2

– ~ 30% of SO2 Addition becomes quickly bound in wines between 60 mg/L and 100 mg/L TSO2

• 100 mg added SO2/ 70 mg free SO2

– ~ 15% of SO2 Addition becomes quickly bound in older wines above 100 mg/L TSO2

• 100 mg added SO2/ 85 mg free SO2

• KMB has 0.576 g of SO2 for every g of KMB

Free SO2 Addition Calculations

1. Determine the amount of Molecular SO2 you need and the volume of wine you will be sulfuring

2. Estimate the amount of binding that will occur after addition

3. Calculate the amount of Free SO2 needed to get the required Molecular SO2 from “The Table” or on-line calculator

4. Calculate the additional Free SO2 needed given the Free SO2 already in the wine

5. Use the correct concentration factor for the method of SO2 addition (KMB vs. pure gas vs. 10% or 6% solution)

Where does Sulfur come from?

Where does Sulfur come from?

Vineyard Sulfur

Vineyard Sulfur

• Useful against Powdery Mildew (Uncinula necator)

– Since 1890’s spray intervals between 7 to 21 days

– Extremely good models of PM growth based upon temperatures between 70° and 85° F

Vineyard Sulfur

• Mutiple forms

– Dust –S with average particle size of 20 to 45 microns

• applied dry

– Wettable –S, dispersants and surfactants

• applied wet or dry

– Micronized – S with average particle size of 5 to 25 microns

• applied wet or dry

• Often discontinued when grapes reach 12 °Brix

• Problem if residue in must > 1 to 10 mg/L

Powdery vs. Downy

• Powdery Mildew on Grapes – Found everywhere in California – Controlled by Sulfur and other

fungicides

• Downy Mildew on Grapes – From Plasmopara viticola – Found in areas with spring & summer

rainfall at temperatures above 50° F – Controlled with “Bordeaux Mixture”

• Copper Sulfate (CuSO4) & Slacked Lime (Ca(OH)2)

Bordeaux Mixture

Hydrogen Sulfide (H2S)

AKA: “Reduced”

Recipe to make something smelly… replace an O with an S

Hydrogen Sulfide fart/rotten egg 1 ppb

3-mercaptohexanol Passion fruit 60 ppt

1,3-hexanediol odorless

Where does H2S come from?

• Vineyard based Elemental S residue

– More S more H2S

– Mechanism not well understood

• S → S2- – Highly yeast strain dependant

– Takes place on cell wall of yeast

– Younger yeast cells produce more S2-

– Higher alcohol produces more S2-

– Amino acid Cysteine may be important

A Brief Detour into Amino Acids

• A class of compounds that have a specific spine and various side chains

A Brief Detour into Amino Acids

A Brief Detour into Amino Acids • Amino acids link together with “Peptide

Bonds” to form Peptides

• Peptides link to form polypeptides

A Brief Detour into Amino Acids • Polypeptides link to form the “Primary

Structure” of proteins

• The “Primary Structure” folds and packs into complex forms like helices and pleated sheets

It is a (Protein) Rave!

Where does H2S come from?

• “Inappropriate” Yeast nutrition – Yeast “leak” H2S when they make 2 amino acids

• Methionine and Cysteine

• Yeast make all organic S containing compounds from the S containing amino acids

Where does H2S come from?

• “Inappropriate” Yeast nutrition

– Yeast “release” H2S when they use S containing amino acids to make other necessary building blocks

– Vitamin deficiency

• Biotin deficiency – Yeast need ~ 1 μg/L

• Pantothenate deficiency – Yeast need ~ 50 μg/L

Where (else) does H2S come from?

• High solids fermentations

• High temperature fermentations

• Lees contact – Release from S containing

compounds in yeast

• Loosley “Bound” to compounds in wine – Poorly understood mechanism

• ???

Removing H2S – The Smart Way

• Copper Sulfate (CuSO4) addition CuSO4 → Cu2+ + SO4

2-

Cu2+ + SO42- + H2S → CuS (s) + 2H+ + SO4

2-

– What matters is the Cu2+

• CuSO4 available as: – CuSO4 (anhydrus)

• white powder

– CuSO4●5(H2O) copper sulfate pentahydrate • blue power

• 10% & 1% (as ? (usually CuSO4))

• Confirm with supplier

Removing H2S – The Smart Way

• According to the TTB (27 CFR Ch 1 24.246)

– “The quantity of copper sulfate added (calculated as copper) (Cu2+) must not exceed 6 parts copper per million parts of wine (6.0 mg/L). The residual level of copper in the finished wine must not exceed 0.5 parts per million (0.5 mg/L).”

• Atomic Mass of Cu2+ = 63.5

• Molar Mass of CuSO4●5(H2O) = 249.7 – So 25.4% of CuSO4●5(H2O) is Cu2+

– 100 mg CuSO4●5(H2O) / 25.4 mg Cu2+

Removing H2S – The Smart Way

• The “secret” about Cu2+

– If there any yeast present, especially live yeast, they will capture large amounts of any remaining Cu2+ left in the wine after addition

Calculation with Cu2+

• 1500 gal of Grenache with a serious H2S problem. Bench trials suggest that you need to add 0.5 mg/L Cu2+. How much CuSO4●5(H2O) do you add?

1500 gal x 3.785 L/1 gal x 0.5 mg Cu2+ /L x 100 mg CuSO4●5(H2O) / 25.4 mg Cu2+ x 1 g CuSO4●5(H2O)/ 1000 mg CuSO4●5(H2O) =

11.2 g CuSO4●5(H2O)

225 L of Chenin Blanc with slight “reduction”. Bench trials suggest that you need to add 0.2 mg/L Cu2+.

How much 1% Cu2+ solution do you add?

– First confirm that the 1% is as 1% Cu2+ (not 1% CuSO4●5(H2O)

225L x 0.2 mg Cu2+ /L x 100 ml Cu2+ solution / 1 g Cu2+ x 1 g Cu2+ / 1000 mg Cu2+ =

4.5 ml Cu2+ solution

Removing H2S – The Dumb Way

• Splash or run Oxygen through the wine

– Splashing will force the volatile H2S out of the wine

– O2 will displace the S in the H2S

2H2S + O2 2H2O + 2 S

• Run the risk of forming thiols/mercaptans from the H2S reacting with acetaldehyde.

Removing H2S – The Dumb Way

• Remember the “coupled reaction” to form acetaldehyde (CH3CHO)

2H2S + CH3CHO → HSCH2CH2SH + H2O

• Ethanedithiol – Highly reactive

• Degrades into other thiols

– Smells like durian

Removing H2S – The Dumb Way

• Ethanedithiol may degrade into:

• None of the above compounds are easily removed from wine – SOME react with Cu2+ slowly (months)

• Thiols can form an equilibrium with disulfides

Compound Aroma Description Concentration in

Wine (µg/L)

Odor Threshold

(µg/L)

Methanethiol

(Methyl mercaptan)

Cooked cabbage,

rotten eggs

0 to 16 2

Ethanethiol (Ethyl

mercaptan)

Onion, rubber, natural

gas, fecal

0 to 12 1.1

Removing H2S – The Dumb Way

• Thiols can form an equilibrium with disulfides

• Disulfides do not react with Cu2+

Compound Aroma Description Concentration in

Wine (µg/L)

Odor Threshold

(µg/L)

Dimethyl disulfide Cooked vegetable,

strong onion

Cabbage

0 to 22 29

Diethyl disulfide Strong onion, burnt

rubber

0 to 80 4.3

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