I did a few SO2 measurements on red wine using titrets. When the first drop of wine gets in, the liquid turns grayish-blue. As I continue to allow more wine in, the hue turns more and more towards the color of the wine. At some point (we'll call it point "A"), the hue seems to be the same as the wine, except that it is lighter (less saturated, like if you diluted wine with some water). After that point, if I keep adding wine, the hue remains the same, and the "amount" of color (saturation) continues to increase until it looks the same as the wine (point "B").
The question is: should I stop at point "A" or "B"?
I happen to agree with Paul. Sometimes you can see the color change easier than other times esp if you dilute the sample first, but even then I have read that you should use an adjustment factor because the reading is off by a certain amount in reds. I gave up on using Titrets for reds because it seemed ridiculous.
Paul says titrets are worthless and I do agree they leave a lot to be desired when testing red wine. But the alternative is pretty complicated and I like laboratory testing. I've noticed that if you keep adding red wine to a titret the redish color stays the same. I keep a used titret (with the red color) around for a reference. When I test a red wine I make sure to add increments of wine slowly, letting any color change develop before adding more wine. If you are careful you can get the color change from dark black to "red" and not add excessive wine sample. For my records I use this first change from dark black to "red" as the end point. And as the color changes I compare it to the "used titret" I keep as a standard. I think this is about as good as you can do with titrets and red wine.
Bill Frazier Olathe, Kansas USA
Franco wrote "At some point (we'll call it point "A"), the hue seems to be
You can get an analysis done from a lab for about $12. To me, this is worthwhile for my wine in 120 liter barrel. If you have small quantities in glass carboys you can guestimate using SWAG (scientific wild ass guess) by keeping track and a record of how much you have added since beginning and during racking. This will probably put you in the ballpark unless you are using a barrel. Here is a link that should help out a lot:
The consensus is not that titrets are useless for red wine. That is just one opinion. If you read some of the good books, like Margalit, or Iverson, they talk about how to use titrets with red wine. If they thought that it was "next to worthless", they would have probably said so instead of explaining how to do it. The consensus is that it is somewhat difficult to find the endpoint, and also that readings are generally too high because some substances like tannins react with the titrating agent. I wish people like Mr. Paul E. Lehmann would not go around expressing their opinions as if they were facts.
Accuvin has paper strip, colour change based tests for several variables, including free S)2. They have 2 colour strips for that one - for low range 0-40ppm and for 40ppm and higher. The cost is about S2.50 per test, so more than titres but less than lab tests. I can't comment on accuracy but heard one good report (no bad).
Vinoferm provides an alternative to titrets. It's also a Ripper test but it works the opposite way, by adding iodine to 10 ml of wine, so the colour change is reversed. The accuracy of reading seems better because the scale is linear across the range, not like titrets. I've been using it for whites instead of titrets, but did only one test so far on reds - I remember the reason was that the result was much lower than what I got by titrets, so I didn't know which test to believe. Either that or I did the test wrong. I'll give it another try soon as I have some reds close to bottling.
For the Vinoferm test, the iodine solution has a short shelf life, that's the main drawback. On the other hand, it encourages frequent testing as the cost is all up front and the solution life is limited. So I'm finding it's cheaper and safer overall than titrets.
The "eyeballing" approach of guessing how much sulfite wine needs is too rough in my experience. I tend to do this on whites in the early stages and on reds in general because of the endpoint determination issues, and the result in general is the wines get more sulfite than they need.
For example, I've made some Riesling and Gewurz this year, both cold fermented and stopped with some residual sugar. The only sulfite addition was 40-50 ppm when I was stopping the fermentation. After this the wines were racked once, fined with bentonite and sparkalloid, cold-stabilized outside for 2-3 months, racked again, and filtered with MiniJet through #2 pads once and #3 pads twice. After all this, the sulfite is now between 20-28 ppm now, and it's the first time I can't smell it on the finished wine. The point being that if I didn't test before filtering and retest after, I would have had added at least another 40ppm to each batch and ended with a sulfite bomb. The pH on these is 3.1-3.2, that's why the sulfite is so noticeable.
If you continue reading, you will find other experts who state that they are next to worthless for red wine analysis. If you like them and trust them for red wine, then by all means use them, but, MOST people will find them next to worthless. YOU will be misleading people by telling them that they are accurate for determining SO2 in red wines.
If you have a "significant" quantity of wine in barrel, do you advocate using questionable data or spending $12 to get an analysis? Remember, you are not only risking the wine but the barrel itself by exposing it to contaminated wine.
Franco, I still use titrettes on red wine but do consider the practice questionable, that's why I haven't commented on this thread until now. I have both of those books and Margalit does not necessarily say that using titrettes on reds is acceptable. Titrettes are a reverse Ripper test so I do see what you are getting at, if you follow his procedure to the tee and gain the experience necessary to see the red disappear in the sample you can try it. Both he and Iverson note that tannins among other things interferes with this method. He recommends a few other chemicals beside the titrettes for his process too. Iverson's procedure is simpler but there has to be a reason Margalit tells you to add H2SO4 and starch. I'm not a chemist, I'm an Instrumentation and Controls guy so I just follow the process when i don't know enough about what to question.
I guess what soured me on them is two things.
One, I have had a red come out slightly effervescent in the bottle, it could have been a little residual sugar, it could have been ML. The wine is good but not something I would give away, it's flawed.
The other thing is Chemetrics, the manufacturer of titrettes. They specifically state they are not designed for red wines. I'm assuming that is due to the interference from the other constituents normally present in reds
I am considering setting up for an AO measurement process but I make enough and am geeky enough to think it's worth it. I would not suggest that is the right way to go for someone making 30 gallons or less of wine a year.
Don't get me wrong, I'm not trying to be argumentative, I'm just saying they are not cut and dry with reds as I see it.
Don't put words in my mouth. I never said that titrets are "accurate" for determining free SO2 in red wines. I am saying that they are not "next to worthless". Must everything be black or white? If you study science or engineering, you will know that there is no such thing as something being accurate. Experiments are accurate enough or not accurate enough according to the requirements. So titrets might not be accurate enough for you and your large batch of wine aging in a barrel, but they can help a home winemaker with 5 gallons of red who wants to know whether his free SO2 is closer to 10, 50, or 100 PPM. Can you see the difference?
Thanks for the info Pp. I've been looking for a way to avoid an A-O set up so these kits interest me. Accuvin tells me thier S02 kits (suitable for both red and white wine) have a shelf life of 4 months and they're working on trying to extend that. Do you recall what the Vinoferm shelf life is?
I did a search for the Accuvin SO2 test and someone here had contacted the Accuvin about the shelf life and it is only 4 months. Interesting that in the same thread, Tom S. says that the iodine for the ripper test will last a long time if stored properly. Still, it seems like a lot of lab equipment and other supplies are necessary, plus the setup time is lengthy for the ripper test.
I won't post a link for the thread (started by Paul, incidentally) since it turns out extremely long but a search of Accuvin SO2 will turn it up
I posted a thread awhile back lamenting the lack of a good test for SO2 for those of us making small quantities of red wine (5 gallon batches). No one had a good answer except for the lab test which seems a little much for small batches. If the Accuvin had a longer shelf life I would give it a go.
Sure hope a better method comes along soon, because this is the number one area of winemaking that I struggle with the most. I don't like guessing on the SO2 but don't want invest a small fortune in money and time in the tests.
Incidentally, for those of you who send samples to a lab. How many times do you send the sample for one batch of wine? It seems to me this should be done at crush and then again every time wine is racked and also at bottling. At $12 a pop plus the waiting for sample results, this appears to be the drawback to me.
Ya know, this just started to make me think.... I'm wondering if I can't find a membrane to selectively pass SO2/EtOH/H20. H+ would come thru as well. If said membrane exists, this would be an easy read, in theory, assuming 'free' SO2 doesn't rapidly dissipate. We used to use membranes at work to selectively pass a whole slew of chemicals, and the surfaces could be treated as needed for greater or less selection.
Interesting thought Mkike- thanks for triggering it.
I haven't seen the shelf life mentioned explicitly anywhere for the Vinoferm kit, but I'd used one batch for at least 3 months and even at that time the result was very close to a titret comparison on the same white wine. So it looks comparable to the Acuvin strips.
I usually sulphite to 50ppm (depending on pH) when I put in barrel. I then send off a sample after a few months. After a while you can get an idea of the rate of loss and adjust accordingly. I send off a sample before bottling.
It may seem like a lot but - for example a 120 liter barrel holds 12.5 cases of wine when bottled. It takes about 400 pounds of grapes to make this wine. If you assume just $1.00 a pound, that is $400 right there. If the wine goes bad, you have lost the $400 and you are without that wine for another year - put a value on that. Also, if you contaminate your barrel, you are looking at another $200 to $400 right there. To me, sending off a sample several times at $12 bucks a pop is worth it. When I start drawing my Social Security in another 11 months I am going to invest in AO apparatus. I have tried, titrets, Accuvin and find neither acceptable to me. Some people may have more calibrated eyeballs than my chronologically advantaged ones and things like the Accuvin may work for you.
If this discrepency range fits your needs, then go for it. I assume, however, that most people test for SO2 in order to make future decisions and not just get a number for curiosity sake only. I want accurate numbers when I make a decision on how much SO2 to add. If the value is between 10 and
50, this is simply not accurate enough for me and I think it is wrong to advise others that it is acceptable - unless they know the facts and are willing to take the risk. I have tried the titrets and compared them with lab results. It is still my opinion that they are worthless - there is just too much discrepency.
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