SO2 Testing Question for Masta and others

[Hal Maulden]

Scott,


I was talking with George today and he stated that you had done lots of work with SO2 analysis. So have I. Could you share your research?





Hal

 

[masta]

Hal,


What part of SO2 analysis are you interested in.... method of testing?

 

[Hal Maulden]

Thanks for the reply. Yes, the analysis. I am a chemist by trade so this comes very natural. I have tried the titrets. They work OK but they are very expensive. I also bought the Iodate/Iodide from Cellar Supplies before they closed and it seemed to work ok, until here recently. It seems to be off now, but I don't have any chemicals to do a standardization with. Have you tried the Vinofern (sp?)? I am now getting into MLF and I need to control the SO2 a little closer.


Thanks for your insight.


Hal

 

[masta]

Hal,


I put on the lab coat this morning and ran some tests and here are the results:


I made up a solution of water and K-meta and used a calculation (11.3 L water and 0.3 grams K-meta powder) which should have given me 15 ppm fee SO2. The problem is the sulfite calculator assumes 50% of the sulfite will become boundin your must or wine so the total sulfite is actually 30 ppm. I am not sure if any sulfite becomes bound in water.


Ran 2 tests on water/meta solution with the Iodate/Iodide from Cellar supplies and both testsshowed 25 ppm of free SO2. Which appears fairly close to the original calculation


Ran 2 test with the Vinoferm Acidometer/Iodic (SO2) Solution and both tests showed only 10 ppm of free SO2.


Looking back on past testing it appears the Vinoferm tests usually came out lower then the Iodite/Iodide.I have been using theIodite/Iodide from Cellar Supplies because I think it is easier to use and since you are counting drops is more accurate.


The Iodic (SO2) Solution for the Vinoferm has a limited shelf life and must be kept refrigerated and mine wasn't for a period of time so it could be no good causing faulty results.


Note: I ran all testing by placing a measured amount of solution in a 30 ml beaker with stirring bar on a Magnetic Stirrer.


Sorry I couldn't be of more help with my testing results. Since Cellar Supplies is closed do you know where can I get more reagents for that kit?

 

[Hal Maulden]

Masta:


Thanks. I am trying to find a source for the Iodide/Iodate. If I can find something to standardize this with I will buy the base chemical and make my own.


I tried to titrate just plain water yesterday with the I/I solution and it came out like 50 ppm??????????? Can you try this and see what you get? The scales I have only weight +/- 2 grams so I am kind of limit to what I can do at home.

 

[masta]

I just ran 2 tests on my well water:


water straight from the tap: 6 ppm


water from my reverse osmosis system: 6 ppm

 

[Hal Maulden]

Masta,


Success....Iodide supply


[url]http://www.wine-testing-supplies.com/ccp51/cgi-bin/cp-app.cg i?usr=51F629639&rnd=5965792&rrc=N&affl=&cip= &act=&aff=&pg=prod&ref=assembly3 [/url]


Hal

 

[Hal Maulden]

Masta,


Success #2 for Iodide


http://www.piwine.com/pdf/cat23.pdf





Hal

 

[Hal Maulden]

Masta


Net info





http://vinquiry.com/analytical_protocols.htm





Hal

 

[masta]

Thanks Hal, I will be looking through that info later today

 

[Joseph1]

Scott and Hal,<?amespace prefix = o ns = "urnchemas-microsoft-comfficeffice" />

I am not familiar with the SO2 kit from Cellar Supplies. Do you measure out a sample of wine, add starch and sulfuric acid and then titrate with iodine? Does the supplied iodine indicate its strength? The first link has iodine that is 0.0156N and the others are different. With a small sample of wine, the difference in iodine strength could be significant.

 

[masta]

Joseph,


The SO2 kit from Cellar Suppliesuses a 10 ml sample of wine and then add 1 dipper (included in the kit) of Acid Starch Indicator and mix well. Drops of Potassium Iodide-Iodate 0.0156N are added until while mixing until sample turns blue.


Number of drops x 2.0 = ppm of freeSO2.

 

[Joseph1]

I am not a Chemist nor have I taken a class in Chemistry, so I don’t know if the Potassium Iodide-Iodate solution in the Cellar Supplies test kit is the same as the Iodine solution used in the Ripper Test on the other sites. Perhaps Hal can tell us. <?amespace prefix = o ns = "urnchemas-microsoft-comfficeffice" />

I had no success in finding Potassium Iodide-Iodate 0.0156N. If Iodine 0.0156N turns out to be the same, you may also want to check www.redbirdservice.com.

 

[masta]

Thanks Joseph and I had the same question about the Iodide-Iodate.


I am assuming that since the starch indicator has acid in it there is no need to add it separately like with other test kits.

 

[Joseph1]

I would agree that the acid starch indicator takes the place of the sulfuric acid in the other tests. This may also prove difficult to replace.

 

[Hal Maulden]

Joseph and Scott,





Sorry for the late reply. We had our holiday Thursday, golf Friday and Saturday, and today is my B-day.


On the iodide solution. You can use any normality solution you want. You can make up for the difference with the following calculation:


((mls iodine solution) x (N of solution) x 32000)/sample size in MLS


On the acid: You must have an acid environment for the SO2 to be liberated and titrated. If you regular (non acid) starch indicator you will need to add some type acid. Or, you can use an acidified starch indicator.


You can also use a syringe to titrate with and save the money that a buret cost. The accuracy is fine for this test.





Hal

 

[bilbo-in-maine]

Will the result of this discussion be that a recommendation be made for
appropriate SO2 test kits or components for the average home winemaker to
purchase? I've been following this with much head scratching hoping it
might be the case - an inexpensive, fairly easy way to check free SO2 by
someone who is chemistry-challenged.

Bill

 

[Joseph1]

Bill<?amespace prefix = o ns = "urnchemas-microsoft-comfficeffice" />

The SO2 test method being discussed is the Ripper method. Because of pigments, aldehydes, etc. in the wine, it tends to result in a SO2 reading higher than the amount of free SO2 present. This is particularly a problem with red wines.

Another problem is that the iodine reagent solution deteriorates quickly when exposed to light. It must be stored in a dark place. Unless the iodine solution is periodically standardized the results will be off (another test).

The wine sample size will also affect the accuracy. If you are using a 10ml sample of wine, each 0.1ml of 0.02N iodine solution represents 6.4ppm of SO2. Increase the sample of wine to 50ml and each 0.1ml of iodine represents 1.28ppm of SO2. Using a larger sample will use more chemicals but the results may be more accurate given the limitations of the method.

To assemble the equipment and chemicals to perform the test using the Ripper method will run $30 - $40. More accurate results can be obtained with the Aeration Oxidation method, however the equipment and chemicals will set you back a few hundred dollars.

For the chemistry-challenged (myself included), Titrets are available http://www.finevinewines.com/ProdDetA.asp?PartNumber=5412. They work okay for white wines but are difficult to read with red wines. Since they are based on the Ripper method, they also read high.

I do not test for free SO2. I cannot afford the equipment to be accurate and I don’t want to spend the time for results that are not. If I had a reason for knowing the approximate free SO2 level (malolactic fermentation, bulk aging for 12 months, etc.), I would test using the Ripper method. Being in the ballpark is better than being in the parking lot.

Somewhere in my files I have the procedures for performing the test with the Ripper method. If I find it, I will post it for those interested in expanding their winemaking laboratory.

 

[Joseph1]

The following procedure for testing free SO2 appeared on another website sometime ago. One of the chemicals is soluble starch solution. You can purchase 1% or 2% starch solution or make your own (Mix about 1/2 a teaspoon of corn starch in a cup of cold water, bring to a boil and use when cool). The commercial solution may have a mold inhibitor. If you notice discoloring of the solution you made, make a fresh batch. You will also note that the formula for calculating the free SO2 appears different. For a 50ml sample of wine it is the mathematical equivalent of the one Hal had posted earlier. If you use a different strength of iodine solution or a different sample size, use the formula Hal had posted. <?amespace prefix = o ns = "urnchemas-microsoft-comfficeffice" />


“The standard Ripper test is quite easy to do on white wines, but can be difficult to do on reds because the color shift is hard to see.

You need a few chemicals:
0.02N Iodine solution
25% sulfuric acid
soluble starch solution (Be sure to boil this if it's been awhile since you used it, or if making fresh.)

You also need some glassware:
10ml graduated pipette (disposable is OK)
50ml graduated cylinder (Nalgene is best for this)
Reaction vessel (I use a 500ml wide mouth Erlenmeyer flask for this, but you could use almost any clear vessel - e.g., a jelly glass, small Mason jar, even a wine glass.

Measure 50ml of wine using the graduated cylinder and dump it into the flask. Add a few drops of the starch solution. Just before titrating add ~10ml of the sulfuric acid to the flask. Fill the pipette to the zero mark and add iodine solution to the flask with constant swirling. Watch for the endpoint in the flask, which is a color change to a faint, persistent indigo, going dropwise as you get close. Read the volume of the iodine off the pipette and calculate the free SO2.

ml iodine *(0.02 * 20 * 32) = ppm free SO2

It takes a bit of practice to do, but it isn't all that difficult. The only expensive item is the 0.02N iodine solution, which must be kept in a dark place when not being used.

You don't need a 50ml volumetric pipette for measuring the wine or a fancy burette with a stopcock on a ringstand to get good readings with Ripper. Simple tools will get you a number that's plenty good enough for your purposes. Your technique at measuring the volume of iodine required and spotting the endpoint are what's most important.”

 

[bilbo-in-maine]

Joseph - Thank you very much for this information. It is still quite
daunting, collecting the pieces of equipment, finding sources for the
chemicals, following the directions...

It makes me think that maybe most home winemakers fly by the seats of
their pants, using standard rules of thumb like 1 Campden tab per gallon
every other racking (kits excluded), 1/4 tsp k-meta per 6 gallons, etc. I
think I sometimes worry more about over sulfiting than under.

Thanks again,

Bill