Iodine test for starch question

[YeastHerder]

I went to the local pharmacy and got this. The label says it is 2% Iodine. Here is what I saw:

water + corn starch: ++++++ (+'s indicating the amount of blue perceived)
water only: -
mash @ 5 minutes: ++++
mash @ 60 minutes: +

I was surprised to see a decent amount of color even after an hour mashing at 152F. The recipe I was mashing contained about 70% pale 2 row, 30% crystal malts. Is it typical to see that residual starch? Is that the unfermentables from the crystal malts?

I also tested my iodine on a paper towel and it instantly turned black as night, unlike I've seen in some posts. Is my % Iodine too high? I'm basically using 1 drop Iodine solution to 1 drop of mash on a ceramic plate (because the paper towel by itself was turning black).

 

[Reno_eNVy]

You might be getting a false positive from the super ridiculously high amounts of crystal malts. Dude seriously, you going for toffee beer?

 

[YeastHerder]

You might be getting a false positive from the super ridiculously high amounts of crystal malts. Dude seriously, you going for toffee beer?

Pretty much. I'm making 1 gallon test batches to get a sense of what different grains contribute, sort of like doing a SMaSH, but subbing 30% of the base for different grains. The ones I tested were 30% crystal 40 and 30% crystal 60. The raw worts weren't as caramel-y as I had expected really.

At any rate, if its the residual non-fermentable dextrins then it isn't a false positive. I would think that something similar would be seen when comparing a light-bodied beer to a full-bodied beer too. I'm just wondering because the instructions I've seen for doing an Iodine starch test claim that there will be no reaction when the mash is done, but the description of what makes a full-bodied beer 'full' contradicts that.

 

[Andrew5329]

Iodine tests are a qualitative test not quantitative. You will never get perfect starch conversion. Ever. Which means that your indicator test will still show a slight slight starch content no matter what. The Walgreens link you posted isn't directing me to a specific product, but all you really need to do is put a drop of wort on a white saucer, and put a drop of regular yellowish Iodine on it. If it turns black you have lots of unconverted starch, if its a light brown you got good conversion (the lighter the better).

That said in your case you used a lot of crystal malt so you should expect a lot of unfermentable starches (maltodextrin for example) which will show up on an Iodine test.

It's really just a quick test we use in the Bio labs for various experiments, outside of using a scientific Spectrophotometer to measure the exact wavelength changes coming off your sample you wont get a quantifiable answer on the exact % conversion. Even the +++ system of your kit is only a rough approximation with potentially arbitrary thresholds.

 

[YeastHerder]

Awesome, thanks.

 

[TrickyDick]

I recently switched from a dropper bottle of iodine solution I bought when I lived in St Louis over 6 years ago, to Lugol's solution that I get from work after it expires.
I was brewing yesterday and mashed for like three and a half fricking hours!
I had been so used to the iodine solution, which I stored I my 90+ degree garage, which was basically useless at that point. I would do the test, and it would never show anything, so I would think all was good. In fact it was just old and useless. I compared my new Lugol's solution to this old bottle of indicator, and the old bottle was false negative every time. however, the Lugol's was ALWAY positive. I am trying to re-learn how to mash it seems, based on this lugol's iodine test.

It's been cold outside, and my burners not working the greatest. with 13 gal of mash in the mash tun, i think there is a temp differential from the top to bottom even recirculating. I kept testing and testing, and mashing and mashing, and then I started to think, like outlined above, that if the unfermentable crystal malts (10% of my grist) was causing a false positive. Anyway, exhausted and frustrated, I just finished it up and moved on with the brew.

Lately I have been using white sidewalk chalk (could use drywall board also) as I read about on braukaiser.com good info there, but i do not recall information about crystal malts and such causing a "false positive". the chalk seems easier to read and interpret as compared to a white saucer.

TD

 

[broadbill]

I stopped using iodine to check conversion...converted mash always seems to come up with some faint blue/black which I attributed to the husk/starch granules that were present in the sample.

I've never had a mash not convert. With today's highly modified 2-row, 90% of conversion is happening in the first 20-30 minutes.

To me, its more trouble than its worth. Since its qualitative it doesn't really tell me anything useful anyway. The most useful experiment would to test the mash as various time point to see the conversion from deep blue/black (starch) to brown (conversion)...but since conversion happens so quickly now, that really hard thing to "catch".

Tried the chalk methods of brewkaiser and that wasn't any better than a saucer, in my opinion.

 

[GlowingApple]

I compared my new Lugol's solution to this old bottle of indicator, and the old bottle was false negative every time. however, the Lugol's was ALWAY positive. I am trying to re-learn how to mash it seems, based on this lugol's iodine test.

Sorry to bump an old thread, but I'm having the exact same issue, so wondering if you ever found a solution? I am using Lugol's as well and every test I do comes back positive, even after mash-out.

 

[TrickyDick]

I describe two issues in that last post so not sure which you are having.

I can no longer get lugol's and the stuff is mighty expensive from what I recall. Used to get "expired" droppers from work which would have otherwise been discarded. It does keep for a few years.

What I've been doing is using a piece of white chalk (the large sidewalk type- I acutally bought a case of railroad markers they're called so I'll have a lifetime supply - was the only way I could find any..) instead of a plate. I use the method described on the Braukaiser.com website.

Its best to pull a sample at the beginning of the mash and test then save the chalk so you can compare to the end of the mash. Starches that cannot be enzymatically reduced by the mash are always present in most mashes to some degree and I have come to the assumption/conclusion that it is those starches that cause the iodine reaction.

Overall, the intensity of the reaction should dramatically decrease at the end of your mash.

What are your pre and post fermentation gravity readings showing? Do you trust the readings on your thermometer in the mash?

TD

 

[Redlantern]

I decided a little when ago to iodine at 30 min on the mash for reference then again at 60. If I think it needs an extra 15 min I will go with that. If no change between 60 and 75 min, I start my fly sparge

 

[GlowingApple]

I describe two issues in that last post so not sure which you are having.

I can no longer get lugol's and the stuff is mighty expensive from what I recall. Used to get "expired" droppers from work which would have otherwise been discarded. It does keep for a few years.

What I've been doing is using a piece of white chalk (the large sidewalk type- I acutally bought a case of railroad markers they're called so I'll have a lifetime supply - was the only way I could find any..) instead of a plate. I use the method described on the Braukaiser.com website.

Its best to pull a sample at the beginning of the mash and test then save the chalk so you can compare to the end of the mash. Starches that cannot be enzymatically reduced by the mash are always present in most mashes to some degree and I have come to the assumption/conclusion that it is those starches that cause the iodine reaction.

Overall, the intensity of the reaction should dramatically decrease at the end of your mash.

What are your pre and post fermentation gravity readings showing? Do you trust the readings on your thermometer in the mash?

TD

I have Lugol's (also an expired bottle from my school), and all of my tests on chalk come back positive. I run a test at dough-in to have a confirmed positive, but the subsequent tests are nearly as dark. I used SG to confirm my last brew's conversion. Samples every 15 minutes showed 9.2 Brix, 14.2 Brix, 16.2 Brix, 16.8 Brix (60 min), 16.5 Brix, 17.8 Brix (90 min), 17.5 Brix. So I called it good after 105 minutes, but did a mash-out just to be sure.

I discovered that if I took a sample from the wort before stirring the iodine test on chalk came back less positive, maybe negative, but if I took a sample after stirring it was always positive. During mash-out I took a sample before and after removing the grain bag, tested both on chalk (both were positive), and then let the samples settle while boiling. I tested them later on and they were both negative.

So maybe I'm getting false positives from the fine flour in the mash? Would diluting the Lugol's help?

EDIT: Forgot to mention that my OG for my last batch was 1.055, and I was expecting 1.056, so pretty close. The previous time I brewed this beer I had the same issue, and only got an OG of 1.052, so adjusted some things for this batch. My FG for that beer was lower than I wanted, 1.009, but I think that's due to another issue, losing heat during the mash.

I'm pretty confident in my thermometer. In ice water it reads 32.10 ˚F and 211.00 ˚F in boiling distilled water.

 

[broadbill]

I have Lugol's (also an expired bottle from my school), and all of my tests on chalk come back positive. I run a test at dough-in to have a confirmed positive, but the subsequent tests are nearly as dark. I used SG to confirm my last brew's conversion. Samples every 15 minutes showed 9.2 Brix, 14.2 Brix, 16.2 Brix, 16.8 Brix (60 min), 16.5 Brix, 17.8 Brix (90 min), 17.5 Brix. So I called it good after 105 minutes, but did a mash-out just to be sure.

I discovered that if I took a sample from the wort before stirring the iodine test on chalk came back less positive, maybe negative, but if I took a sample after stirring it was always positive. During mash-out I took a sample before and after removing the grain bag, tested both on chalk (both were positive), and then let the samples settle while boiling. I tested them later on and they were both negative.

So maybe I'm getting false positives from the fine flour in the mash? Would diluting the Lugol's help?

EDIT: Forgot to mention that my OG for my last batch was 1.055, and I was expecting 1.056, so pretty close. The previous time I brewed this beer I had the same issue, and only got an OG of 1.052, so adjusted some things for this batch. My FG for that beer was lower than I wanted, 1.009, but I think that's due to another issue, losing heat during the mash.

I'm pretty confident in my thermometer. In ice water it reads 32.10 ˚F and 211.00 ˚F in boiling distilled water.

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Interesting. My recommendation would be to dilute the mash liquor for testing instead of the Lugols.