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-   -   Iodine Test (http://www.homebrewtalk.com/f36/iodine-test-81728/)

IllusionOfTime 09-25-2008 12:53 AM

Iodine Test
So, I'm in the middle of my first partial mash, and I want to make sure that all of the sugars have converted... I've checked the Wiki, and I haven't see anything noted of the Iodine test...

I watched Yuri's video's a while back where he did the test, however I can't find it currently. I think that I remember that I just put Iodine on a white surface, and then a spoonfull of the mash liquid and it should be a color, however, I do not remember the proper color...

So, I've got about another 30 min or so on the mash, so I'll obviously be checking back fairly often... :)

BrianP 09-25-2008 01:27 AM

I wouldn't worry about it. If you mash for 60 minutes at a decent temperature (150-156, depending on the maltiness you want), it will very likely be fully converted. I've never done an iodine test and probably won't ever do one.

s3n8 09-25-2008 01:33 AM

If I remember correctly, purple color means starch, black means sugar.

ifishsum 09-25-2008 01:37 AM

It turns black with starch, if it's fully converted the color will stay yellow/orange.


Starch Test: Add Iodine-KI reagent to a solution or directly on a potato or other materials such as bread, crackers, or flour. A blue-black color results if starch is present. If starch amylose is not present, then the color will stay orange or yellow. Starch amylopectin does not give the color, nor does cellulose, nor do disaccharides such as sucrose in sugar.
BTW, I've been wondering - is there any reason one could not use a drop of Iodophor to perform this test?

TheH2 09-25-2008 01:53 AM

I've read on here that idophor works. I haven't tried it.

Joe Camel 09-25-2008 02:17 AM

Yes, iodophor works. I use the technique from Braukaiser's Wiki, dab some wort on a piece of sidewalk chalk, then a drop of iodophor. If it turns black, starch. If it stays yellow, no starch. Carve chalk with chisel to expose clean surface and you're ready for the next test.

IllusionOfTime 09-25-2008 02:21 AM

Excellent, I did the mash at ~155 for 60 min so I think that I'm good. I did the test and it didn't turn black, so I think I'm in the clear. Good times. Thanks... :)

portlandbeergeek 09-25-2008 03:51 AM

I'm kinda colorblind and I don't really see much of a difference in the iodine between "fresh" (5 mins in) and "ready" (60 + mins, obviously converted) mash. Is there another way besides tasting for sweetness? Some past tests will turn yellow in my eyes after a quick swirl on the white plate. I assume this means conversion? Any other colorblind imput would be well appreciated. For the record, I have trouble seeing greens against prime colors and purples against reds/blues.

fratermus 09-25-2008 05:32 AM

The converted results are pale; the unconverted results are dark. It's a pretty stark contrast. This is a much clearer indication than you will normally get, but for comparison purposes:


In this picture, the left tube is positive for starch. Right is negative for starch.

TheH2 09-25-2008 12:34 PM

Not completely a color thing, but I've noticed that when opening the mash tun, if the top of the wort has sort of an iridium shine to it then it is converted. The best way I can explain it is the shine you get off of a bubble solution (soap and water).

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