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General Category => All Grain Brewing => Topic started by: imperialstout on February 04, 2013, 02:05:19 PM

Title: Will clear / decolorized iodine work for the starch / full conversion test?
Post by: imperialstout on February 04, 2013, 02:05:19 PM
Wondering if the clear, decolorized iodine will work for the starch / full conversion test. My guess is it will if it is the iodine that changes colour and not the colour added to the iodine that changes. My guess is if there is no starch left the clear iodine will stay clear, otherwise it will turn purple. Any thoughts?
Title: Re: Will clear / decolorized iodine work for the starch / full conversion test?
Post by: Jimmy K on February 04, 2013, 02:34:11 PM
Not sure, but there is no dye added to either. CVS lists the ingredients for both and Iodine tincture contains pure iodine and sodium iodine while decolorized iodine contains potassium iodine only. My guess is the answer is no since potassium iodine probably has different properties.
Title: Will clear / decolorized iodine work for the starch / full conversion test?
Post by: denny on February 04, 2013, 04:16:28 PM
Truthfully, I suggest you just skip doing the test.  I know of too may people who get false readings from it and it really doesn't tell you if you have full conversion.
Title: Re: Will clear / decolorized iodine work for the starch / full conversion test?
Post by: Jimmy K on February 04, 2013, 04:52:16 PM
Truthfully, I suggest you just skip doing the test.  I know of too may people who get false readings from it and it really doesn't tell you if you have full conversion.
I've heard that too.  I don't know anybody that still does iodine tests.
Title: Re: Will clear / decolorized iodine work for the starch / full conversion test?
Post by: tschmidlin on February 04, 2013, 05:12:13 PM
I don't do iodine tests either and don't recommend them, but you could put a drop on a slice of bread and see if it changes color.  You'll have your answer.
Title: Re: Will clear / decolorized iodine work for the starch / full conversion test?
Post by: imperialstout on February 05, 2013, 12:22:49 AM
Not sure, but there is no dye added to either. CVS lists the ingredients for both and Iodine tincture contains pure iodine and sodium iodine while decolorized iodine contains potassium iodine only. My guess is the answer is no since potassium iodine probably has different properties.

My brother always said searching for information is like panning for gold, most of the time you just get a few bits but once in awhile you get you get a nugget that make all the effort worthwhile. This was definitely a nugget. Decolorized iodine is a misnomer, it is not iodine that has had the color removed, it is in fact potassium iodine, a different compound. What brewers want is iodine tincture containing 2% pure iodine and 2.4% sodium iodine in a 47% alcohol solution, the remainder being water. Don't know if doing an iodine test is worth it but as someone else said, it is another tool to use to help you make the best beer you can.
Title: Re: Will clear / decolorized iodine work for the starch / full conversion test?
Post by: Jimmy K on February 05, 2013, 12:48:01 AM
I was writing that wondering how different they could be. Then I remembered - chlorine can kill you, sodium will basically explode if thrown in water, but together ... quite tasty.
Title: Re: Will clear / decolorized iodine work for the starch / full conversion test?
Post by: CASK1 on February 15, 2013, 03:18:29 AM
Braukaiser has some really nice scientific info on the iodine starch test here:

http://braukaiser.com/wiki/index.php?title=Iodine_Test
Title: Re: Will clear / decolorized iodine work for the starch / full conversion test?
Post by: imperialstout on February 16, 2013, 04:07:31 AM
Thank you CASK1. That article is everything anyone needs to do an iodine test correctly, and why. Had been using clear iodine, a different compound than the red stuff, at mash temps. Now know to use 1 part regular iodine, mixed with 9 parts rubbing alcohol and do the test at room temp.
Title: Re: Will clear / decolorized iodine work for the starch / full conversion test?
Post by: euge on February 16, 2013, 05:51:31 AM
And by now should be eschewing the use of this test: it is a waste of time. Malt wants to convert. If you have a conversion problem then we need to investigate that instead.