[brian-d]

I've brewed some high gravity beers lately and my attenuation has not been what it normally is (8-10 points high).  Thinking through my process and researching the possible problem I believe my mash was not fully converted and my mash temp may have been too high.  I want to start performing an iodine test to check conversion.  What is the best iodine source for this?  I've seen tincture of iodine 2% at the local drug store and I've also read the idophore would work.  I would appreciate your feedback and experience.  Thanks, and happy holidays to all!

[denny]

Either one of those will work.  IMO, the test is unnecessary and unreliable.  If you mash in the range from 145-160 for 60 min. or more, you will have conversion.  If the problem is that the temp was too high, the iodine test won't matter anyway.

[brian-d]

Again, I've never had such a problem getting my beer to hit the proper FG.  I'm searching for clues.  By the way Denny.  I lived in Noti in the early 60s.  Went to 1st and 2nd grade there.  Lived on Allison Road.  It's a small world.

[denny]

Cool, a Noti-ite!

Have you checked your thermometer calibration at mash temp, not freezing and boiling?  That's one of the first things I look at in cases like yours.

[malzig]

The best way to check for conversion, in my opinion, is to check the gravity of the mash against Kai's Conversion Efficiency chart.  An iodine test will only tell you that the bulk of the starch initially solubilized has been converted to some form of sugar, but starch is being gelatinized and converted past the point where an iodine test is negative. 

[denny]

What was the recipe?  Is it a recipe you;ve made before so you have an expectation for it?  How high was your mash temp?

[Thirsty_Monk]

I would like to point out that higher OG will make higher FG.
what is your OG and FG on your beers?

[davidgzach]

I would like to point out that higher OG will make higher FG.

Is this necessarily true, black and white?  Doesn't a lot depend on the strain of yeast as well?  I've had some high gravity beers ferment way down and some mid gravity beers stop in the mid-teens mainly because of the yeast. 

Dave

[Jimmy K]

Try a longer mash - enzymes will cut more long-chain sugars into more fermentable ones with a longer mash time.  I've never done an iodine test, but hear from many that they don't tell you much. Unconverted starches are likely still in the grain anyway, not in the wort. And conversion is rarely a problem with modern barley malt.

Yeast health is very imported too. Are you making a starter and oxygenating well?

[denny]

I would like to point out that higher OG will make higher FG.

Is this necessarily true, black and white?  Doesn't a lot depend on the strain of yeast as well?  I've had some high gravity beers ferment way down and some mid gravity beers stop in the mid-teens mainly because of the yeast. 

Dave

Only a bit on strain of yeast.  Fermentability of the wort is the key.

[jmcamerlengo]

what base malt are you using? This may also be a consideration for your problem. 

Also as mentioned higher gravity with lower mash temps may need around 90 minutes to convert fully.

[mattc]

Keys for maximum fermentability is making sure your themometers are accurate (as mentioned), mash longer,  mash close to 148-150, make sure PH is in range of enzymes, make sure the mash is not way too thick ( this can prolong the conversion time which could in turn make your mash temp drop over time if you mash in a cooler) , and lastly you can use 6-row brewers malts or more "base" malt for an extra dose of enzymes. The problem may be you have a high percentage of unfermentable specialty malt.

As far as the iodine test goes, I say for the price of Iodine why not use it. I use the iodine that you buy in the drug store for like $2. I bought it 2 yrs ago and I am still using the same little bottle. I disagree that it is a useless test, it will tell you if there are major problems with your mash. It WILL tell you if there are any starches present in the wort. For instance if you have let the mash rest for n hour and you still are getting some purple tinge, it may be a sign that your themometers may be reading wrong or the PH is off and these factors may be inhibiting a full conversion. The downside, like Denny said, it will not tell you how the wort converted: into more dextrine or more fermentables. hope that helps some.

[denny]

As far as the iodine test goes, I say for the price of Iodine why not use it. I use the iodine that you buy in the drug store for like $2. I bought it 2 yrs ago and I am still using the same little bottle. I disagree that it is a useless test, it will tell you if there are major problems with your mash. It WILL tell you if there are any starches present in the wort. For instance if you have let the mash rest for n hour and you still are getting some purple tinge, it may be a sign that your themometers may be reading wrong or the PH is off and these factors may be inhibiting a full conversion. The downside, like Denny said, it will not tell you how the wort converted: into more dextrine or more fermentables. hope that helps some.

One of the main reasons I don't recommend is it that I've heard from so many people who keep mashing for 2, 3, 4 hours becasue the iodine test says they haven't converted.  In almost all of those cases, I believe they've just gotten a false reading.

[morticaixavier]

As far as the iodine test goes, I say for the price of Iodine why not use it. I use the iodine that you buy in the drug store for like $2. I bought it 2 yrs ago and I am still using the same little bottle. I disagree that it is a useless test, it will tell you if there are major problems with your mash. It WILL tell you if there are any starches present in the wort. For instance if you have let the mash rest for n hour and you still are getting some purple tinge, it may be a sign that your themometers may be reading wrong or the PH is off and these factors may be inhibiting a full conversion. The downside, like Denny said, it will not tell you how the wort converted: into more dextrine or more fermentables. hope that helps some.

One of the main reasons I don't recommend is it that I've heard from so many people who keep mashing for 2, 3, 4 hours becasue the iodine test says they haven't converted.  In almost all of those cases, I believe they've just gotten a false reading.

seeing how purple my stainless steel sink turns when I spill idophor no it, even after scrubbing with soap and hot water I can beleive this. It takes only a very small amount of residual starch on what ever surface you are using for the test to give you a false positive. If you have a dedicated white plate or something for your test that you have never used to eat pasta or potatoes or whatever from it might be useful. Someone mentioned in another thread that the brewer at SN said he always does a test even though 99.9% of the time it's not really necesary because that .1%  he has caught potential problems that way but I suspect they have better equipment for the testing than we do.

[tubercle]

I used to test every batch but after about 50 batches with no positive starch results after 60 minutes I didn't find further testing pragmatic.