Iodine test never comes back fully positive

[vitaminb]

Hi everyone,
So, I wouldn't say I'm an advanced home brew guy, but I've successfully done several 5 gallon extract batches that were very successful. I don't have a lot of the expensive equipment, but I'm still pretty new to all of this.
Recently, I've been trying out small one gallon all grain batches just using a pot to mash, monitoring the temp as closely as possible.
I read about the iodine test being used to check for starch conversion, and also that I may need to mash for longer than an hour to fully get a positive read on the test.
Although I realize I'm doing a pretty inefficient mash, my problem is that my iodine test never comes back positive or even close really. Last night I kept the temp between 148 and 158 for almost 2 hours in order to try to convert the starches and get a better reading, and while the iodine test was lighter, it wasn't near where it should be. I've tried several times and get the same result
The OG on the batch should have been around 1.065 and I read it as about 1.038.
So what's going on? Sorry, I'm a newbie here, but what can I do to get a better OG? Was the temp maybe too low for a lot of the time? Too high?

 

[MichaelBrock]

Are you looking for the correct "result" in your iodine test? What you are looking for is for the iodine not to turn blue/purple. If it stays brown after adding it to your wort (make sure there are no grains in your sample; apparently this can contaminate the test) then conversion is complete.

 

[broadbill]

I see a similar problem with the iodine test, where I get a "faint positive" for starches, even after a long mash. It makes me think the iodine test doesn't work all that great for this application, and I've actually stopped doing it. Plus, I get pretty dry beers, all the more reason to think its not indicative.

A good thing to do is to do a positive control (iodine test at the start of the mash) to get an idea of a true positive starch test, then base your other iodine tests on that.

 

[LandoLincoln]

Testing "positive" for starch means that the iodine will turn blue or black if starch is present, and that's what you don't want. If it stays brown, then you've fully converted the starches to sugars.

Small bits of grain in the sample may give you false positives, so try to get a sample that doesn't have any bits of grain.

 

[LandoLincoln]

Last night I kept the temp between 148 and 158 for almost 2 hours

You need to get better control over that temperature. Mash temps are pretty darn critical, compared to other stages of brewing. Try to stay within 2 degrees of your target temp for the full duration of the mash (usually only 60 minutes).

A sheet of aluminum foil over the top of the grain bed helps to keep the heat. It's pretty amazing how well something that simple works.

 

[broadbill]

Small bits of grain in the sample may give you false positives, so try to get a sample that doesn't have any bits of grain.

I expect this is the crux of the issue. I'm thinking that to get the types of efficiency we typically expect (70-80%), we are crushing so fine that the mash is filled with very small starch pieces that throw the test off. For me, it is virtually impossible to get a clean sample to test.

Interesting test would be to mash what would be considered a bad crush and compare to a good crush. I would predict that the bad crush would have a lower efficiency, but it would have a more cut and dry iodine test associated with it.

 

[ajdelange]

You have to be careful in your conduct of the test in order to get meaningful results. You should withdraw some liquid from the mash tun carrying as little solid material as possible with it (I didn't say 'no solid material' because that's not possible). Place a drop or 2 of this on a white porcelain surface. Place a drop of tincture of iodine next to the wort drop so that it flows up to and contacts the wort drop. Look for color at the interface. No change in color means complete starch conversion. Reddish color means mostly converted with dextrines present. Blue or black means unconverted starch. If the liquid touches any solid grain bits they will turn deep blue or black. This is normal even with complete conversion.

If the 'white porcelain surface' is a dinner or other plate be sure to wash the iodine off thoroughly after the test.

 

[Misplaced_Canuck]

Also... Don't use a plate that's been around the unmashed grain, because grain dust will give you a positive.

If you want to know what you're looking for, mix a little bit of corn starch with some water, on a plate, and add iodine. It'll become very obvious.

MC

 

[daksin]

Another thing may be some flour in the test sample which can throw positives, though most flour should still be getting converted. To eliminate this problem, try sucking up the wort into a paper towel by just barely touching a corner into the mash. Then, let it spread up into the paper towel. Put your iodine on the spot furthest from the corner to be sure. Also, check the paper towerl to make sure it doesn't throw its own false positive.

What source of iodine are you using? Still, I think conversion efficiency due to uncontrolled mash temps is your likely culprit.

 

[BigEd]

Hi everyone,
So, I wouldn't say I'm an advanced home brew guy, but I've successfully done several 5 gallon extract batches that were very successful. I don't have a lot of the expensive equipment, but I'm still pretty new to all of this.
Recently, I've been trying out small one gallon all grain batches just using a pot to mash, monitoring the temp as closely as possible.
I read about the iodine test being used to check for starch conversion, and also that I may need to mash for longer than an hour to fully get a positive read on the test.
Although I realize I'm doing a pretty inefficient mash, my problem is that my iodine test never comes back positive or even close really. Last night I kept the temp between 148 and 158 for almost 2 hours in order to try to convert the starches and get a better reading, and while the iodine test was lighter, it wasn't near where it should be. I've tried several times and get the same result
The OG on the batch should have been around 1.065 and I read it as about 1.038.
So what's going on? Sorry, I'm a newbie here, but what can I do to get a better OG? Was the temp maybe too low for a lot of the time? Too high?

IMO with modern malts an iodine test is not only a waste of time but you are perhaps more likely to get a false negative than a positive. If you expose modern malt to a warm, aqueous environment it will convert, no worries.

 

[ajdelange]

Yes, I think I agree that it's a waste of time. I haven't actually done an iodine test since I can remember as I have never had a wort appreciably lower in OG than what I predicted. There are other ways to tell that conversion has been effective. The mash turns dark, becomes easier to stir, the liquid becomes a bit syrupy and, finally, it tastes sweet.

 

[Misplaced_Canuck]

Another thing may be some flour in the test sample which can throw positives, though most flour should still be getting converted. To eliminate this problem, try sucking up the wort into a paper towel by just barely touching a corner into the mash. Then, let it spread up into the paper towel. Put your iodine on the spot furthest from the corner to be sure. Also, check the paper towerl to make sure it doesn't throw its own false positive.

NO GO! I often use paper towels with iodine solution on them to clean stuff. The paper always turns purple with iodine! There's a viable source of "starch" in there.

MC

 

[broadbill]

I've also seen where someone took a sample by dipping some chalk in the mash....it didn't work well for me, but maybe I did it wrong.

 

[Denny]

The iodine test is so unreliable (and unnecessary) that I stopped doing it years and several hundred batches ago. I advise new brewers to try it once so they can see what it is, then forget about it.

 

[amandabab]

we all like gadgets and tests.

But you can tell more just by looking at the top of the mash than an iodine test will tell. It's just pointless procedure.

 

[vitaminb]

First of all, this forum is amazing. I didn't expect this many responses so quickly, and everyone has been cool.
So, yeah, I should have mentioned that I did the chalk iodine test where you take a chunk of chalk and a drop of wort and a drop of iodine.
Still, it sounds like the iodine test isn't the way to go.
Instead of worrying about testing, should I just try to better regulate the temp? Make sure the grain is crushed better? I was shooting for an OG of around 1.06 and I only got to around 1.04 after two hours. Again, all I'm using is a pot for now for one gallon batches.
Also, amandabab, what did you mean that I can tell more looking at the top of the mash? What am I looking for?
Thanks again for all of the responses! The iodine test was driving me crazy, so it's good to know that it's so unreliable.

 

[Denny]

I really doubt your low OG was due to incomplete conversion. If you really want to know what's going on, check Kai's conversion efficiency work...http://braukaiser.com/wiki/index.ph..._Efficiency#Determining_Conversion_Efficiency . Conversion occurs between 130F and 165F. If you spend long enough in that temp range (90 min. at the lower end, 45-60 min. at the higher end) you WILL have conversion.

What amandabab meant was that as the mash converts, the liquid sitting on top of it becomes very clear. That's a good indicator of conversion.