Iodine test

[Clint]

Hello all
Whilst finalising my next shopping list and then researching sparging I came across testing the mash for starch using iodine. Does anyone do this and is it reliable etc?

Cheers

Clint

 

[whealsie]

Yep. I do it every time. Dead easy and super reliable. A bottle of iodine is a couple of quid and you only need a drop. If there is any blue/ black keep mashing and test again after 15 minutes. Nothing to lose.


I love the smell of mashing in the morning.

 

[Sadfield]

Only bother if I'm doing something out of the norm, but it is handy to have if you suspect something isn't right.

Sent from my E5823 using Tapatalk

 

[foxbat]

I do it every time. To be honest it's probably not required as you'd have to really mess things up in a way that I can't even fathom to not have full conversion after the common 60 minute mash. However it's one of those positive confirmation steps that you can look back at if you have a problem and say for certain that it wasn't your mash that failed.

 

[Clint]

Thanks all!
I suppose it's just another step in the learning curve and another tool to use...plus it looks really clever in front of gestapo headquarters!

 

[AlanHarper]

I was investigating the use of Iodine to test the carbohydrate conversion and had trouble getting a small cheap source from local Pharmacies until I came across one in Amazon. It is a set of 30 odd cotton bud swabs with iodine in the stick - you break the stick and the iodine is released. I have ordered them as they are less than £2 with free posting. The can be found here: http://amzn.eu/grSznMU. I'll let you know how they perform.

 

[Bigcol49]

Hi!
One alternative method is to take regular refractometer readings to determine the gravity of the wort. Iodine is cheaper than a refractometer!

 

[AlanHarper]

These Iodine Sticks work a treat. Crack one at the end and rub the cotton bub in the wort sample... easy
Link: http://amzn.eu/d/0PUdVJD

Amazon sell them
BENHAI 1 PC Disposable Medical Iodine Climbing 30pcs/pack Medical iodine - cotton swabs iodine - disinfection outdoor household handling small wound bobs Cotton Bars = £3.98

 

[BeerCat]

Does nascent ioidine work or does it have to be the cheap stuff?

 

[peebee]

I remember iodine tests! I do have to think back a bit though.

You scoop out a teaspoon of grainy mash, add a drop of iodine, and all the grain turns black. I'm sure it wasn't supposed to but what could I do about it? In the end I just stopped bothering with it. It's one of those tests that if you are unsure what you are doing, it'll make sure you know that you don't know what you're doing. Yippee!

 

[Hoppyland]

I remember iodine tests! I do have to think back a bit though.
You scoop out a teaspoon of grainy mash, add a drop of iodine, and all the grain turns black. I'm sure it wasn't supposed to but what could I do about it?

Yep, pretty much my feeling. I still have a bottle of iodine that must be 30 years old now. I always got blackness back then, but the beer seemed fine.
Nowadays, my mash temperatures are usually well within 2 degrees of where I want them, I mill my own, fairly recently bought, grain. I normally mash for over 60 mins. What else could I do if the iodine test said "NO"?
Anyway, this has intrigued me so on my next brew, I'll resurrect the iodine test. My mash efficiency is normally about 85% so no worries! But after reading this thread I'll pop some iodine onto the residue. I will definitely expect some blackness, but I'll be intrigued to see the result.

 

[simon12]

I have never done it but a while ago I read about it and read that if there are any grain pieces in what you test it will go black as the grain will have some non soluble starch or something like that.

 

[JohnB]

I've tried this iodine test - I use Lugol's iodine in some microscope work (staining bacteria) so I always have some kicking about on a shelf. It seems a bit hit and miss to me, cos Lugol's will turn starch black if the starch is within about 2 miles of the stuff! I mash for 60 mins, take a few drops of the strained wort and add a single drop of iodine, it turns black, then brown, then clears. I think, bu**er this, I'll ferment it anyway. I end up with wort at 1040 at 20 DegC and I'm happy. Even more so about 3 weeks later!

Take a sample of wort, cleared of as much grain as possible, place this in a white porcelain dish, you can buy special starch test dishes. Add a drop of iodine, any iodine will do. "Lugol's" is elemental iodine dissolved in potassium iodide in water. But you can use tincture of iodine as well. If there is any starch there, it will turn black. As the iodine dilutes in the wort, it will turn brown and finally dis-colour.

To be fair, Iodine is an excellent indicator of starch (the best for a rough test of starch), but I bet you could mash for 24 hours and still find a bit of starch in the mashed grains/liquid.

I'd be interested if anyone has a more accurate quantitative test for starch though? -- without an entire lab available --

 

[Henders]

I do it purely because when I was wondering around the local home brew place paranoid I'd forget something the name 'iodine' popped into my head and I asked if he had it. Little bottle. Cheap.

I got blue/black when I tested the little beer during an experimental/ill-conceived parti-gyle session. I'd added more pale to balance stuff out and was rushing things a bit.

But yeah it makes me feel more Dr. Scienc'ee :P

 

[strange-steve]

There's an alternative way to check your conversion using some simple maths, which I found to be pretty accurate. @Bigcol49 will like this I reckon.

You can work out the theoretical maximum extract of the wort then compare that to your measured gravity which should be pretty close at the end of the mash, ie within 10%.

The formula is:
Max extract = 320 / (mash thickness in kg/L + 0.8)

This gives you the gravity points, ie. the bit after the decimal point in the SG, for 100% conversion efficiency.

 

[Bigcol49]

Hi!
You're right @strange-steve I like it
Does that formula apply to all types of malt?

 

[strange-steve]

Hi!
You're right @strange-steve I like it
Does that formula apply to all types of malt?

Well it's purely theoretical and based on certain assumptions, and different grists will have different extract potential, but it should be close enough to let you know how the mash is progressing. I've used it a number of times and always been within a few points

 

[JohnB]

@strange-steve I like that idea and will definitely give it a try, it seems more useful than trying to detect starch when you flipping well know it's there right from the start! But being able to predict what I should be getting before-hand, then a simple check of the gravity seems a good 'un to me. Do you guys check at a specific temp, i always try to chill an OG test down to 20 DegC - 68 DegF before testing - I read that somewhere - does that sound about right, please?