Iodine test (starch haze)

[The-Engineer-That-Brews]

I have come across a few references to doing an iodine test on the mash liquor, as a way of knowing when the starch has all been converted. But I was never really too sure why I might be interested in doing this - after all, if the wort is at the target SG then who cares, right?

However today I came across this on Braukaiser:

Brewing wort should show no visible reaction with iodine, This means that no glucose chains longer than about 9 glucose molecules are present. Otherwise the beer can suffer from a starch haze that is difficult to remove. This haze is actually not caused by starch but by large dextrines which become less soluble as the alcohol content increases during fermentation [Narziss, 2005].​

Ahaaa…! OK, perhaps I need to get some iodine.

 

[moto748]

I've often thought abut it too, but never done it. I have a batch of bitter bottled that is stubbornly refusing to clear; only bottled 12 days, but rare for me for it to be so cloudy at this point. I'll leave it as long as it takes (within reason). I wonder if it is suffering from such a starch haze.

 

[The-Engineer-That-Brews]

Looking on Amazon shows a range of different iodine products - several under the guise of food supplements and hence at a ludicrous markup.

Do It Yourself | Causes of Color suggests that to do an iodine test:

You can use Betadine (a povidone-iodine mixture), Lugol’s solution (an iodine-potassium mixture), or tincture of iodine (here the iodine is dissolved in alcohol, or alcohol and water), depending what is available. They all have a very strong color, so dilute the mixture with about 10 parts water to see the reaction more clearly.​

They seem to have betadine, as long as you don't mind having the instructions in Serbo-Croat... but at that price I think I might ask the pharmacist in boots if they have anything similar...

https://www.amazon.co.uk/Betadine-100mg-ml-30ml-EGIS/dp/B088LJ3QSM

 

[Buffers brewery]

https://www.the-home-brew-shop.co.uk/tincture-of-iodine-30ml-home-brewing.html

 

[The Baron]

i did it a few times when I started AG but do not bother now

 

[foxbat]

i did it a few times when I started AG but do not bother now

Same here. Did it for quite a while and it never showed anything but positive results so I don't bother any more. Maybe if I try a heritage malt like Chevalier then I'll do the test again.

 

[Buffers brewery]

Thinks. If I'm going to have problems with my brew day and hitting the targets it's usually recipes involving oats and/or wheat. Maybe I'll find my iodine next time to see what I get.

 

[The-Engineer-That-Brews]

You guys who are always getting positive results, just to play devil‘s advocate but does this mean you could reduce your mash time?

 

[The-Engineer-That-Brews]

https://www.the-home-brew-shop.co.uk/tincture-of-iodine-30ml-home-brewing.html

Thanks @BB !

 

[The Baron]

I do a 45 Minute mash and have done for ages unless I am doing a overnight then I do a 30 minute step mash@ 62c then 30 minute @68c.
The latter gives me a efficiency of usually 80 or more against 70 to 75 with a standard single mash

 

[foxbat]

You guys who are always getting positive results, just to play devil‘s advocate but does this mean you could reduce your mash time?

Probably, but one hour nicely takes in having a shower, going to the shop for the paper and eating my egg and toast breakfast

 

[The-Engineer-That-Brews]

I do a 45 Minute mash and have done for ages unless I am doing a overnight then I do a 30 minute step mash@ 62c then 30 minute @68c.
The latter gives me a efficiency of usually 80 or more against 70 to 75 with a standard single mash

Yes, 30 + 30 is similar to what I do too, although I sometimes take the first step up to 63-64°c in the hope of getting a bit of combined alpha+beta

 

[An Ankoù]

I have come across a few references to doing an iodine test on the mash liquor, as a way of knowing when the starch has all been converted. But I was never really too sure why I might be interested in doing this - after all, if the wort is at the target SG then who cares, right?

However today I came across this on Braukaiser:

Brewing wort should show no visible reaction with iodine, This means that no glucose chains longer than about 9 glucose molecules are present. Otherwise the beer can suffer from a starch haze that is difficult to remove. This haze is actually not caused by starch but by large dextrines which become less soluble as the alcohol content increases during fermentation [Narziss, 2005].​

Ahaaa…! OK, perhaps I need to get some iodine.

I did it for years, nay, decades. Iodine dissolved in aqueous potassium iodide works well. Look at any of the Castle Maltings recipes and they all intone "do the iodine test". If you're mashing for 60 minutes or even 90, it's worth doing. I tend to leave my mash for hours or even overnight as it fits in better with my working day. There's no real need to test for starch end point with a long mash.

 

[The-Engineer-That-Brews]

Incidentally, without wishing to be a complete geek on this stuff (yeah, I know… too late) it seems that the iodine test can be used for more than just telling when the mash conversion is complete:

 

[marshbrewer]

I use Videne for sanitising, can I use that?

 

[RoomWithABrew]

Don't use Vosene it'll make your beer all foamy.

I don't bother with the Iodine test, last Mash efficiency 89% with an hour mash. Rice lager I made a while ago cleared fine and rice is basically all starch. Had a terrible job getting a speckled hen clone clear with windsor yeast and flaked wheat in the recipe, it took months in the bottle to clear and then they were all gushers unless chilled to the extreme and cracked several times to release the pressure.

 

[The-Engineer-That-Brews]

I use Videne for sanitising, can I use that?

Try putting a spot of it on the cut surface of a bit of potato - if it turns dark blue then yes

 

[An Ankoù]

Don't use Vosene it'll make your beer all foamy.

I don't bother with the Iodine test, last Mash efficiency 89% with an hour mash. Rice lager I made a while ago cleared fine and rice is basically all starch. Had a terrible job getting a speckled hen clone clear with windsor yeast and flaked wheat in the recipe, it took months in the bottle to clear and then they were all gushers unless chilled to the extreme and cracked several times to release the pressure.

Don't add it to the beer at all. Just a small sample of the beer, a teaspoonful is enough, and then throw the sample away.
Back in the day when a 90 minute mash was standard, I had, perhaps, one in 20 brews where I had to extend the mash time to complete conversion. Now that recipes are calling for a 60 minute mash, I would have thought the starch test was even more important. Unless you're brewing a hefeweisen or one of the cloudy, alcoholic fruit juice non-beers, of course.

 

[marshbrewer]

Indeed, It seems such a quick and easy step, that it makes sense to do it anyway; at least until you have your process completely nailed?

 

[Sadfield]

You guys who are always getting positive results, just to play devil‘s advocate but does this mean you could reduce your mash time?

Not really, it depends what type of wort you want to finish with. It only shows that you've converted starch to sugar, as the OP points out, of 9 chains or less. If I'm brewing a Saison for example I will still want a long mash length to get a highly fermentable wort composed of shorter chains. It's all about balancing time and temperature and the way a and b-amylase work in order to control fermentability.

There's a lumberjack analogy. Felling a tree is conversion, cutting it into logs takes further time. Longer to cut logs into planks, branches into fire wood, firewood into small kindling, and so on.