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Old 04-18-2012, 11:22 PM   #1
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Default Iodine for Starch/Sugar test

I just did my first all grain batch. One of the steps was was to test for the completeness of starch to sugar conversions was the old high school iodine test. I bought a "tincture of iodine" from Rite Aid. Unfortunately, it was "decolorized", which appeared yellow and stayed yellow on both a slice of bread and a pile of flour, meaning I had no way to measure the conversion

Does anyone do this test and where do you get the correct form of iodine to check for remaining starch?

Thanks.

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Old 04-18-2012, 11:41 PM   #2
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Do you use iodophor sanitizer? Because that works.

If not, why not just great straight up iodine instead of a tincture?

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Old 04-19-2012, 11:33 AM   #3
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It appears that "straight" iodine is not easy to come by at the retail drug stores.

I did see that others, like you, have suggested iodophor as the best option.

My local brew supply shop has it, so that's what I'll will use.

Thanks.

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Old 04-19-2012, 05:18 PM   #4
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I spent a while trying to find proper iodine, and finally read something stating that in my state they can't sell it anymore. Apparently it can be using in making meth. So the tincture is the way to go, at least in some states.

I found some tincture (providone-iodine) at Walmart, and saw some more at a Rite-Aid. And THEN I finally saw some at my LHBS.

I also want to mention that you will want to add a few drops of the solution to your mash sample, and then stir it in. The first couple times I had done this test I had omitted the stirring and was generally confused why it wasn't changing color. But after stirring, the reaction should happen. I always do this test now before sparging.

--Jimbot

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Old 04-19-2012, 05:46 PM   #5
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The iodine test is a waste of time IMO. You can easily get false results and even if you get good results it tells you nothing about the state of the sugars you have. If you really want to know if you have complete conversion, use Kai's spreadsheet and look at the gravity.

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Old 04-19-2012, 05:50 PM   #6
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Quote:
Originally Posted by Denny View Post
The iodine test is a waste of time IMO. You can easily get false results and even if you get good results it tells you nothing about the state of the sugars you have. If you really want to know if you have complete conversion, use Kai's spreadsheet and look at the gravity.
Yea if you are getting grain husks in your sample, yea -- it can be false. But iodine test is a good tool, especially for noob AG brewers for indicating when conversion is complete.
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Old 04-19-2012, 06:29 PM   #7
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I'm sorry, but I just can't agree it's a good tool when I so often hear "I mashed for 4 hours and the test says I still haven't converted". Just forget about it...if you mash for 60 min. at the proper temps and pH, you WILL have conversion. And there's a wide range of temps and pH that will work. You have to be wildly off on both to not convert. And like I said, if you want to check, a far better tool is http://braukaiser.com/wiki/index.php...ion_Efficiency

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Old 04-19-2012, 07:40 PM   #8
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I've never had a false positive for starch when using iodophor for testing.

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Old 04-19-2012, 07:42 PM   #9
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I use it simply because if I get good conversion at 45 minutes I go ahead and start sparging. A couple of drops and some time saved.

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Old 04-19-2012, 08:03 PM   #10
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Quote:
Originally Posted by Denny View Post
I'm sorry, but I just can't agree it's a good tool when I so often hear "I mashed for 4 hours and the test says I still haven't converted". Just forget about it...if you mash for 60 min. at the proper temps and pH, you WILL have conversion. And there's a wide range of temps and pH that will work. You have to be wildly off on both to not convert. And like I said, if you want to check, a far better tool is http://braukaiser.com/wiki/index.php...ion_Efficiency
I'll use that formula next time I brew and see how it goes, especially since I just got an auto-temp correcting refractometer. But if an iodine test fails after that long -- I imagine the brewer either doesn't know how to take a clean sample or overheated and denatured the conversion enzymes and botched the mash.

But I like the iodine test -- especially as a BIAB'er since most people suggest 90 minute mashes when doing BIAB. When an iodine test is clear @ 45 minutes, I can mashout immediately, hit my calculated OG, and save 45 minutes on the brew day and be confident I didn't leave any starched unconverted.
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