VWT 272 Class 10 Quiz 9 Number of quizzes taken 24 Min 11 Max 30 Mean 26.5 Median 28 Mode 30
Lecture 10 Some Chemical Structures and the Sulfur Dioxide Family The difference between professional winemakers and armature winemakers is how much SO 2 they use. Ed Moody Retired Senior Winemaker Bronco Winery
Plan of Study More chemical structures Alcohols Carbonyl Groups Aromatic Rings Phenols The Sulfur Dioxide Family Sulfite Bisulfite Molecular SO 2
More Fun with Chemical Structures! Alcohol A compound with a hydroxyl group ( -OH ) bound to a saturated carbon atom Methanol Methyl Alcohol, Wood Alcohol Poisonous» Metabolized to Formaldehyde Used to denature ethanol Ethanol Ethyl Alcohol, EtOH, Alcohol Cause Intoxication Found in fermented foods Propanol Two forms» n-propyl alcohol solvent» iso-propyl alcohol Rubbing alcohol
More Fun with Chemical Structures! Carbonyl Group A functional group with a double bonded Oxygen atom ( =O ) bound to a carbon atom Aldehyde Strong Odor (Sherry, Green Apple) Hangover Ketone Strong Odor (Fruty) Hangover Breath Carboxylic Acid Vinegar Amino Acids Ester Strong Odor (Fruty/Floral) Lipids (Fats & Oils)
Even More Fun with Chemical Structures! Aromatic Ring Structures A closed ring structure of 6 Carbon atoms with a single Hydrogen attached to each Carbon Benzene Sweet/Spicy odors NOT cyclohexane
Even More Fun with Chemical Structures! Aromatic Ring Structures Common in Nature Lots of groups can attach to the ring Polycyclic lots of rings can attach to each other
Yet More Phun with Chemical Structures! Phenol A compound with a hydroxyl group ( -OH ) bonded to a Aromatic Ring Phenol Polyphenol Flavonoid» Quercetin
Yet Even More Phun with Chemical Structures! Phenol Huge structures Polymers Lignin Bakelite
A brief History of Sulfur Dioxide (SO 2 ) Ancient Egypt used to bleach Linen Ancient Greece - Used as a fumigant The Odyssey Book XXII Odysseus himself spoke to Eurycleia, his faithful nurse: Old woman, bring some sulphur, and make a fire, so I can purge the hall from this pollution. 1487 - Prussian royal decree officially permitted the use of the wine additive sulfur dioxide Mid-1600s - Introduced into Bordeaux by Dutch traders
Why Add Sulfur Dioxide (SO 2 ) to Wine? Killing and growth inhibition of yeast Killing and growth inhibition of bacteria Inhibition of browning enzyme (polyphenol oxidase) Interaction with wine phenols (bleaching) Binding of acetaldehyde (oxidation taint) Antioxidant Get to use the warning label
Meet The Sulfur Dioxide (SO 2 ) Family SO 2 when added to an acid solution (like wine) exists in an equilibrium between three forms Sulfite SO 3 2- Bisulfite HSO 3 - Molecular SO 2 (aq) Sulfite Bisulfite Molecular SO 2
The (SO 2 ) Family Equilibrium Sulfite Bisulfite Molecular SO 2 The concentration of each family member depends upon ph
Sulfite ion (SO 3 2- ) At wine ph is virtually nonexistent 1 to 3 μm < 0.01% at ph 3.4 Is a good Antioxidant (O 2 grabber) BUT requires much higher ph Example It took 30 days to trap ½ of the dissolved oxygen in an O 2 saturated model wine (tartaric acid + ethanol + SO 2 ) solution It took 2 days to trap ½ of the dissolved oxygen in an O 2 saturated white wine with the same SO 2 concentration
Bisulfite ion (HSO 3- ) At wine ph is Most common form 94.4% at ph 3.0 99.4% at ph 4.0 Is not a good Antioxidant (O 2 grabber) Is not a good Antimicrobial Binds with the carbonyl oxygen in Acetaldehyde Glucose Keto acids Pyruvate Inhibits polyphenol oxidase
Bisulfite ion (HSO 3- ) Binds with the carbonyl oxygen in Acetaldehyde Binds with other carbonyl group containing molecules to form Bound SO 2
Where does Acetaldehyde Come From? Produced by Saccharomyces cerevisiae Then Re-utilized by the yeast More SO 2 at crush increases Acetaldehyde production With 50 mg/l SO 2 added before Fermentation With no SO 2 added before Fermentation Yeast nutrients increase reutilization of Actaldehyde Malolactic bacteria degrade Acetaldehyde during MLF Coupled chemical reaction O 2 reacts with a phenol (catechol) to make Quinone + Hydrogen Peroxide (H 2 O 2 ) Hydrogen Peroxide oxidizes Ethanol to Acetaldehyde On average, red wines contain 30 mg/l, white 80 mg/l, and Sherries 300 mg/l Sensory threshold is between 100-125 mg/l
Molecular SO 2 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 (H 2 O 2 ) to make Sulphate SO 4 2- before it can react with ethanol SO 2 + H 2 O 2 2H + + SO 4 2- Fast CH 3 CH 2 OH + H 2 O 2 CH 3 CHO + 2 H 2 O Slow Sensory threshold 10 mg/l in air 15 to 40 mg/l in wine
ppm = mg/l
Molecular SO 2 The Table
Free vs. Bound SO 2 At wine ph Bound (BSO 2 ) is all SO 2 in the Bisulfite ion (HSO 3- ) form that is bound to Acetaldehyde Glucose Keto Acids Free (FSO 2 ) is all SO 2 in the Bisulfite ion (HSO 3- ) form that is NOT bound + all Molecular SO 2 Total SO 2 (TSO 2 ) = FSO 2 + BSO 2
Free & Total SO 2 Measurement Ripper Method Iodine added to wine Starch indicator goes from colorless to blue Difficult with red wines Yellow light helps Inexpensive Approximate values of TSO 2 & FSO 2 May OVERSTATE FSO 2 by a factor of 2
Free & Total SO 2 Measurement Aeration-Oxidation Method SO 2 is trapped in a in hydrogen peroxide solution after it has been blown/sucked out of an acidified wine sample Methylene Blue/Methyl Red indicator goes from colorless to green Complex setup including vacuum pump and condenser Easy analysis for red and white wines More Precise values of TSO 2 & FSO 2
Forms of SO 2 Gas / High Pressure SO 2 Exact addition Direct measure of grams of pure SO 2 Expensive and potentially dangerous equipment 6% to 10% SO 2 Solution Commercially available Fresh Stock Solutions are accurate Simple to add Potassium Metabisulfate (KMB) Easy to measure by weight Quickly degrades with time Keep package sealed and dry! Inexpensive Simple to add Source of Potassium- cold stability concerns
Free SO 2 Addition Calculations Imprecise GUIDE for SO 2 Addition in Juice/Must Assume ~ 60 % of your added SO 2 will be bound (BSO 2 ) 100 mg added SO 2 /40 mg free SO 2 Concentration will drop rapidly to unmeasurable Damaged fruit will require significantly more SO 2
Free SO 2 Addition Calculations Imprecise GUIDE for SO 2 Addition in Wine ~ 50% of SO 2 Addition becomes quickly bound in young wines and wines below 60 mg/l TSO 2 100 mg added SO 2 / 50 mg free SO 2 ~ 30% of SO 2 Addition becomes quickly bound in wines between 60 mg/l and 100 mg/l TSO 2 100 mg added SO 2 / 70 mg free SO 2 ~ 15% of SO 2 Addition becomes quickly bound in older wines above 100 mg/l TSO 2 100 mg added SO 2 / 85 mg free SO 2 KMB has 0.576 g of SO 2 for every g of KMB
Free SO 2 Addition Calculations 1. Determine the amount of Molecular SO 2 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 SO 2 needed to get the required Molecular SO 2 from The Table or on-line calculator 4. Calculate the additional Free SO 2 needed given the Free SO 2 already in the wine 5. Use the correct concentration factor for the method of SO 2 addition (KMB vs. pure gas vs. 10% or 6% solution)
Free SO 2 Addition Example 1000 gal tank of Syrah, ph 3.40, FSO2=10 mg/l, TSO2=67 mg/l, using pure SO2 gas, goal is 0.8 mg/l Molecular SO2. How much SO2 gas are you going to add? At ph 3.40 table says FSO2 should be about 35 mg/l With 10 mg/l already in tank (35 10) you need to add 25 mg/l as Free With 67 mg/l TSO2 you would expect about 30% of any addition will be bound. That means for every 100 mg added SO 2 you will get 70 mg free SO 2 25 mg free SO 2 /L x 100 mg added SO 2 /70 mg free SO 2 /L x 3.785 L/gal x 1000 gal x 1 g added SO 2 /1000 mg added SO 2 = 135 g added SO 2
Another Free SO 2 Addition Example 264 gal tank of Chardonnay, ph 3.25, FSO2=3 mg/l, TSO2=32 mg/l, using KMB, goal is 0.8 mg/l Molecular SO 2. How much KMB are you going to add? At ph 3.25 table says FSO2 should be about 25 mg/l With 3 mg/l already in tank (25 3) you need to add 22 mg/l as Free SO 2 With 32 mg/l TSO2 you would expect about 50% of any addition will be bound. 22 mg free SO 2 /L x 100 mg added SO 2 /50 mg free SO 2 /L x 3.785 L/gal x 264 gal x 1 g added SO 2 /1000 mg added SO 2 x 1 g KMB/0.576 g added SO 2 = 76g KMB
Next Week The Other Sulfurs Elemental Sulfide Copper Disulfide