I bought one of those titrets kits. After it turns dark blue i continue to add juice as directed and can never get it back to the original color - as directed. The color change I do get is so gradual that it is hard to determine an end point. It is definitely not as easy as a titration. please help.
marc
I can't help you with Titrets but I'll volunteer that I now use the Accuvin free SO2 tests. They are easy and work with both red and white wines. I found Titretes too difficult to use for reds. The Accuvin kits only have a 4 month shelf life so if you buy them make sure you're getting a fresh one.
RD
If the color is remaining blue-ish and you've added wine/must to the ampule beyond where it would read 20ppm, you don't have adequate sulfite in the wine/must. Add some as appropriate to the volume you're dealing with and re-test. I've found that even with darkly colored wines like blackberry I can see the endpoint, You're looking for the color to return to that of the liquid being tested.
Cal
You must let it rest for about 30 seconds if you aren't sure. If you go too fast you'll get a false reading.
I assume you're doing red wines? White wines are very easily seen... and if yours never change back you may have the wrong sulfite test kit. They make some that go up to 500ppm- you want the one that goes
0-100ppm.try taking a spent sulfite test and stirring in some sulfite... see if that gets it clear for you.
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