TECHNIQUES FOR DETERMINING SULFUR DIOXIDE IN WINE:
THE ASPIRATION METHOD, THE RIPPER METHOD AND THE TITRETTOR METHOD. - W.C. PAETZ   OCTOBER 2, 2003

Abstract:

We employed three different methods to measure the sulfite content of different samples of wine.
The “Aspiration” method involved removing SO2 from the wine by aeration into a solution that oxidized into sulfuric acid. This acid was titrated and the SO2 calculated from the titre volume.
The “Ripper” method involved titrating the wine sample directly with an iodine solution.
The “Titrettor” method involved the use of a prepared reagent sealed in a vacuum ampoule. The result of this test gave the free SO2 in mg/L.

INTRODUCTION:

Sulfur is a preservative, an antioxidant as well as an antiseptic. These characteristics have distinguished this chemical as the silver bullet of wine makers for literally centuries. “Sulfur dioxide (so2) is typically added to the whole fruit or must at crushing. It is a chemical that has been added in various forms to wines since the ancient wine makers of Egypt and Rome learned of it’s ability to prevent wine spoilage.” (1.)
As enologists we will be called upon to discern the exact amount of various chemicals that can help protect our labor of love.
“Knowledge of the actual concentration of free sulfur dioxide and the ability to adjust concentrations to a desired level are of immense importance in fine wine production.” (2.)
The controlling governments’ sanction limited use of this substance in the final product. In the United States the maximum allowable content is 350 parts per million. (350 mg/L)
“Sulfur dioxide permits the storage of many types of wine today that would not exist without it’s protection. In particular, it permits extended barrel maturation and bottle ageing… The adjustment must be made within plus or minus 10 mg/ L.” (3.)

The emphasis on controlling sulfites would be incomplete if I did not mention the U.S. Government requirement. “Since January 9, 1987 wines containing more than 10 parts per million of sulfur dioxide must carry a label statement such as: “Contains Sulfites” (3.)

One can readily discern the value of being able to measure the free and total SO2 in a wine sample at any stage of production. This gives credibility and rationale to support our experiment.

Materials and Methods

Aspiration Method:
1.) 20 mill wine sample Pinot Grigio
2.) 10 mill phosphoric acid 25% solution
3.) 10 mills hydrogen peroxide
4.) 2-3 media drop color
5.) Aspirator with water vacuum 1 l / minute flow rate
6.) Round bottom flask with two peripheral openings plus open on the top with a stopper.
7.) Receiving vile
8.) Pipette
9.) Micro burette

Method:
Flow rate checked. Pipettes submerged into wine. Air moving through the sample pulling free SO2 into the impinger with hydrogen peroxide. 20 mills of wine sample placed into the lower ball beaker. 10 mills of phosphoric acid added to wine sample. Closed with a seal. Impinger add 10 mills of hydrogen peroxide into top flask. Add 2-3 drops of color solution indicator until green. Vacuum checked. Adjust h2o to one liter / minute of air pulled through system. Fifteen minutes. Titrate end point.

Ripper Method:
1.) Pipette 25 ml
2.) Conical flask
3.) Burette with stop cock
4.) Iodine reagent
5.) Safety bulb
6.) 1% starch indicator
7.) sulfuric acid 25% solution
8.) Miller Thurgau wine sample

Pipette the sample 25 ml into a clean conical flask. Add 1-% starch solution with bulb pipette 1 ml. Add 5-ml sulfuric acid. Stir mix.
Place under burette with stopcock drop iodine gradually until color stays after mixing for thirty seconds. Read amount of iodine to change color solution.

Titrettor Method:
1.) valve assembly
2.) ampoule
3.) Sample of wine
4.) Potassium lodate iodide with Phosphoric acid reagent
5.) Wine sample Traminette.

Place flexible end of the valve assembly over the titret ampoule. Fill beaker with wine. Snap the valve assembly at the score mark. Insert in sample and squeeze control bar to extract some wine sample. Wait thirty seconds then continue. Shake titrattor to mix watch for change from blue to clear sample. When end point is observed hold the ampoule in a vertical position and read the scale.
Results
Please refer to table in appendix for results.

Discussion
All of these methods are interesting but certainly one of them must be more accurate. Speed and convenience may not have any relevance here. This is not a measurement that is subject to estimation.

Conclusion
This knowledge is of particular value to anyone who desires to make acceptable wine. I really believe that it would have been useful to use the same wine for all of the methods to see if the results are consistent. If there were a correlation it would be fascinating to observe.
It is also important to note that the SO2 measurement alone means very little if there is a big variance in the pH of the wine samples. The knowledge of these variables together would allow you to make an accurate decision regarding how much SO2 should be added. We need to know how much is bound, how much is free and what the total is. The ability to rapidly and accurately test samples for these data would be of significant value to any enologist.

Appendix

Wine Sample Aspiration Ripper Titrettor
Muller Thurgau 40 46.08 60
Pinot Grigio 12 8.96 16
Traminette 19.2 25.6 42
Chardonnay 5.6 7.68 17

References:

1.) M.W. Baldy Ph.D., The University Wine Course, A Wine Appreciation Text and Self-Tutorial. The Wine Appreciation Guild. (1998)
2.) R.P.Vine, Wine Making From Grape to Market Place.Plenum Publishers (2002)
3.) R.Ribereau-Gayon, Handbook of Enology Volume I, The Microbiology of Wine and Vinifications. John Wiley & Sons Ltd. (2000)

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