I just bought one of those Titrets kits by Chemetrics that came with a "holder" The instructions do not say how the holder works or how to use it. I have never used a Titret before, have no chemistry background and would like some guidance from the group on how to use the holder, and the Titret in terms of tips on using them.
Another question: Lum states in his e-book The Home WineMakers Manual that:
"Winemakers try to maintain 20 to 40 milligrams per liter of free SO2 in their wine from the completion of fermentation until the wine is bottled, but the amount of free SO2 does not remain constant."
If you know that the S02 level is going to drop, why not compensate somewhat in the beginning by adjusting to more than 20 to 40?
The wine I am measuring is a Chenin Blanc from Alexander's Sun Country concentrate in its final stages. Should the s02 level at bottling be between 20 and 30? Will that value be read directly off of the Titret?
KB - Check out this page from the Chemetrics web site:
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I agree, the instructions that come with the Titrets kits are a bit minimal; I think they must figure most buyers are already familiar with them. The critical piece is that they are made with a partial vacuum in the glass tube. When you press the lever on the "holder", that allows some of the wine to be sucked up through the tube into the body of the titret. Hence, the important thing is to keep the open end of the little tube in the wine (so you get wine, not air) and do several very short squeezes of the lever, so that you don't overshoot the color change point. As indicated on the web site, the resulting measurement is obtained by reading the fluid level vs the scale printed on the side of the tube. The numbers on the scale run from about 10 to 100, and the Titrets package indicates that the measurement range is from 10 to 100 mg/L.
In terms of how much SO2 is enough, the precise level isn't really critical, and unless you are planning on extended bottle aging, anything within a pretty broad range will probably be OK.
As you indicated, most sources tell you to measure periodically and adjust the level, rather than adding all of it up front. I think there are two good reasons for this. First, although SO2 concentrations do tend to drop over time, how much/how fast will vary. So there is no precise way to know in advance precisely how much you will need. Second, even if you could predict the total SO2 required over the wine's lifetime, you probably wouldn't want to add all of it in one bit dose up front, as it might inhibit the yeast, would interfere with things like MLF, and might cause other undesirable effects. Your wine would be over-sulfited during fermentation and most of its aging, in order to reach the "right" level at the end of the whole process. It might work out well enough, but it doesn't sound to me like an approach that is going to produce the best possible end result. That's my two cents.
Thanks for the feedback Doug. After breaking the tip and placing it in the wine sample, something came out of the tip and into the wine. That may be normal- the web site indicated there was a starch solution in the tip. Is it normal for that solution to (in the tip) to disperse into the sample?
The final reading was between 15 and 20, I drew sample in to fast (as you warned about) and missed the exact end point. At least it gave me some piece of mind as I had been bulk aging for some months.
Nothing should come out of the tip into the wine sample. Did you slide the rubber tube with the valve all the way onto the ampule (to the white line) before snapping the end of the ampule? Yes there's a starch solution in the ampule, but it shouldn't come out due to the vacuum in the ampule.
I slid the tube all the way over the ampule and then snapped. When I placed the tube in the sample, before squeezing the tube, you could see the mixing of the contents of the tube with the sample. However, the ampule turned almost black, and stayed that way until about the 10 marking on the ampule (it then started to fade). At 15 it was almost back to the original color of the sample. Something did definitely come out of the end into the sample. Is the test still valid?
I have no idea - but your observation made me go back and look at the titret information sheet. I really hadn't paid attention to whether there was anything in the valve assemble that you put onto the ampule, and found out there is. Supposedly it has approximately .05 ml of phosphoric acid - which I can see in the harder plastic tube ahead of the valve. I assume this needs to get into the ampule when you press on the valve, to acidify the wine sample that goes into the ampule and release the SO2 to react with the reagents in the ampule. If, for some reason, the phosphoric acid is going out of the valve assembly rather than into the ampule, you are probably not getting an accurate test result - unless Chemetrics assumes a small amount will come out and it doesn't matter. That's my interpretation at least - why don't you send an e-mail to Chemetrics
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and select "Technical Questions") and see what they say. If you do that, please share what you hear from them.
I wrote chemetrics as suggested and asked the following questions:
1) Is it normal for liquid to appear at the titret tip after snapping the score?
2) Is it normal for liquid from the titret to enter the wine sample?
3) Will the results be accurate (in this case 15 mg/l was indicated).
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