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ayoungrad · 03-04-2011, 01:31 PM

I posted this question in the middle of another (not entirely relevant) thread and did not get an answer.

I do BIAB. Before I did my first few BIAB batches I bought Tincture of Iodine for starch conversion testing. I looked for Lugol's but could not find it (thanks to drug addicts everywhere) but it is my understanding that the main difference between the two is that Lugol's does not use alcohol for solubilty and that both should work for starch conversion testing.

I say all of this because I ran the test several times on the first few BIAB batches I did. I would take a small amount of the wort, place in onto a white plate and then put 1-2 drops of the tincture into the wort. Early in the mash it would turn black immediately but even up to 2 hours into a mash, it would still slowly turn a "light" black. I never went more than 2 hours for any of these mashes despite the absence of a "clean" starch test.

I have since stoppped testing because I found it so unhelpful. I run one hour mashes and have had great/expected efficiency, attenuation and FGs. And the beers have been good. (BTW, on my original posting yesterday I only mentioned efficiency. I woke up this morning realizing how almost irrelevant efficiency is to this discussion.)

So why would I continue to get a semi "incomplete" result with iodine testing? My only thought (aside from the possibility that I'm doing something completely wrong) is that I'm getting little bits of grain in my sample which will never completely convert to sugar. But if that is the case, wouldn't everyone fail to get a complete conversion iodine test?

Thanks in advance.

Nateo · 03-04-2011, 03:06 PM

The reason most people don't do iodine tests is because most people aren't formally trained to read one. It's actually something that takes a lot of training to do accurately.

"So why would I continue to get a semi "incomplete" result with iodine testing? My only thought (aside from the possibility that I'm doing something completely wrong) is that I'm getting little bits of grain in my sample which will never completely convert to sugar."

Yes, you're right. Draff will cause a false-positive in the iodine test.

**nilo** · 03-04-2011, 03:31 PM

Most people that mash grains do that in a mash tun and not a BIAB system. Runnings from a mash tun will turn very clear and without any big particles, so a iodine test always work.
I have tested many times and didn't do anything special, I'm not formally trained, and I always got good results.
May be one using a BIAB process could pass the wort thru a coffee filter first before testing.

DeafSmith · 03-04-2011, 03:39 PM

Here's some info on how to do iodine tests:

http://braukaiser.com/wiki/index.php/Iodine_Test

ayoungrad · 03-04-2011, 03:48 PM

Thanks for the link and thanks for the all the reponses.

Learned a new word... I had never heard of draff before. The article does say this will cause a false reading.

I was taking my sample from outside of the bag so it is sort of filtered. There are never any large particles, just tiny ones. But maybe a coffee filter or the like would be a helpful idea to try. I'll have to try it.

**ajdelange** · 03-04-2011, 05:02 PM

Particles in the mash liquid will always test deep blue.

The best way to get a meaningful test is to take some liquid from the mashing vessel (tun, bag....) up with a teaspoon. Try to exclude husk material. Place a drop of this liquid on a smooth, white porcelain plate. Place a drop of tincture of iodine next to the drop of wort. The two will run together. Read at the interface between the drops. Ignore dark specs from particulate matter in the wort.

If the plate is one you eat from be sure to wash all the iodine off and run it through the dishwasher before using it to serve food again.

If the mash:

1. Turns dark
2. Becomes easier to stir
3. Tastes sweet

you don't really need an iodine test. It has converted.

**nilo** · 03-04-2011, 05:49 PM

Quote:

Originally Posted by ajdelange

If the mash:

1. Turns dark
2. Becomes easier to stir
3. Tastes sweet

you don't really need an iodine test. It has converted.

This doesn't make sense to me.
An iodine test is to know if one had a "FULL" conversion, meaning no starches left.
Conversion will alsways happen, a full coverstion, not always.

**ajdelange** · 03-04-2011, 06:51 PM

I guess what I should have said is that after you have done a few of these you will stop doing them because you will always have some pink/orange from residual dextrines, will have noticed that your efficiencies are good, will have noted from malt spec sheets that saccharification times are from 10 - 20 minutes and will stop wasting your time on iodine tests. If you get the three indications I mentioned in the last post and let the mash sit for 20 minutes at a reasonable temperature, you will be as converted as you are going to be. I can't think of anything that would cause a mash to go to 75% of normal and then not the rest of the way (recognizing, of course, that completion is approached asymptotically). As part of the learning process, by all means do iodine tests but eventually you will find they aren't telling you anything you don't already know.

ayoungrad · 03-04-2011, 07:09 PM

That is essentially what I've done. Except I mash for 60 minutes.

You only do 20 minutes mashes? For all mash temps? For all mash thicknesses?

**ajdelange** · 03-04-2011, 07:33 PM

Not really. Most of my brewing is lagers. The length of the "rest" is, I suppose, the sum of the time you let it sit plus the time it takes to pull the next decoction and get it started upwards in temperature. Then throughout the the decoction 60% of the mash sits at saccharification temp. Thus 40 % of the mash gets a 30(?) minute rest and 60 % gets an hour and a half. When I do non German ale or stout I guess I let it go about 40 minutes knowing that most people let their ales go longer but confident that I've gotten about all I'm going to get. An iodine test never showed anything other than conversion as complete as one can detect with an iodine test after 20 minutes or so.