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Iodine test

I’m looking for a little clarification on testing for starch conversion using Iodine. Basically BLACK mean that there is still starch present. RED/ BROWN means the starch has been converted to sugars, is this basic info right?

Yes, this is correct. The iodione will turn blue/purple in the presence of starch. If you see just an amber color (which is the color of the iodine), there is an absence of starch. I never do the test.If you’ve hit mash temps reasonably well, and your chemistry is not way off, you should have full conversion after an hour, and likely before then.

+1 to skipping the test. Not only is it unnecessary, it’s easy to screw up and get a false reading. Taking a gravity reading and using Kai’s conversion efficiency tables … Efficiency works a lot better if you want to do anything at all.

I always do an iodine test, more as a feel good kind of thing.

Recently I made a beer with a high percent of corn and low mash temp, let it sit for an hour and was ready to start my run off but did the test first. It showed starch still present. Let it sit another half hour and all was well.

It doesn’t cost much in money or time, so I don’t see a downside.

You do have to keep in mind that if you get bits of husk in your sample they will show as starch.

The only downside from my perspective is that it can give you a false negative. Mashes that are only 85% converted will show iodine negative, according to the stuff Kai has posted on the subject. I still check my conversion, but I use the refractometer because of this issue.

I’ve also never been able to read the reaction really well, I need to try the drop on chalk thing. Whenever I tried it before I didn’t know what ratio of iodine to wort to use, so either the iodine became really dilute or I used too much iodine in the wort and it all looked brown.

That’s the problem I seem to be having too, the ratio of wort to iodine. also the iodine that I’m using (an “antiseptic solution”) is only %10 iodine, is that enough?

I did the test for my first five or six brews. Seems like a waste of time to me now. When you are confident in your mashing meathod and even come remotely close to correct temperatures there are no problems.

The only time I would think about it might be if I were trying an extremely short mash. But even then I probably wouldn’t do it.

Once you try checking your conversion efficiency, you’ll see the iodine test for what it is…outdated and inaccurate. After all, conversion efficiency is what you’re trying to measure with iodine. Why not use a more accurate and informative method?

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