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For some reason my iodine test does not indicate full conversion, even after a 1 1/2 hour mash. Our water has a relatively hight ph, 7.0. I tried using 5.2 PH stabilizer, but it didn't seem to help much. Despite this the gravity comes out just where I would expect it and the wort tastes sweet. Fermentation takes off and it ferments down to relatively low gravities. Beer seems to come out fine. Does iodine go bad? or am I missing something.
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As in the previous reply, iodine tests can be somewhat indistinct at times, especially if you're just dropping iodine solution onto a wort sample. The method can be refined as follows:
Take a small quantity of wort in a sample bottle (eg. McCartney)
Add methanol until it forms a dense white precipitate
Allow the precipitate to drop, then pour off the excess methanol
Add a small quantity of distilled water, just enough to redissolve the precipitate
Add iodine dropwise
This will give the usual blue-black colouration for starch, but also shows more clearly the presence of dextrin with a brick-red colouration.
Done this way the test is sensitive enough to quantify the results as 'trace' as well as just positive/negative.
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