Originally Posted by Denny
The iodine test is so often wrong that I advise people to not even bother. If you know you've been at 150 for 80 min., you've gotten conversion.
I've never had it be wrong, and i have had wheat mashes take 90+ minutes to fully convert. Eventually it does test negative as long as you have a clean sample. One drop of wort and one of iodine on a white paper towel or piece of chalk, and it's very reliable.