iodine starch test??

[beer gut]

Hi everyone i hope you are well. Anybody who won any place at the compition in skipton well done!!. I have a question about doing a starch test usin iodine, i have used this method twice now and i must admitt iam not sure on what iam doing with this test.What i mean is after 1&half hours of mashing when i test the grain with odine i get a the colour green now even when i have mashed after 2 hours i still get the colour green. Now does this mean that all the starch has been converted caus it has not gone blue? or does the green colour is indication that there is still starch present in the grain? I have tried testing the grain after 45 min mashing and the colour is a purpley blue, but iam still not 100% sure on this colour green. Any advice or thoughts would be of great help.

[HighHops]

I use iodine in work to test for starch and it goes green on it's way from purple/blue to yellow. So green is sort of half way, but I would consider it starch free but only just. You should also bear in mind that 10% of males are colour blind. So what you call green might be yellow for me.
If we are both firing on a full set of cones then maybe you should test your thermometer that you use for your mash. When I've mashed for just an hour at 66C my iodine test is yellow, which means complete conversion of starch to carbohydrates.

Hope this helps.

[EoinMag]

Here's a comprehensive wiki article on the iodine test.

http://www.homebrewtalk.com/wiki/index.php/Iodine_test

I do my testing on a white plate myself.

[steve_flack]

Actually it works really well on a piece of chalk. You put a spot of the wort on the chalk and a drop of iodine and see the result. When you're done just cut that bit off the end of the chalk.

[boingy]

A couple of things:

1. Make sure you are not including any grain/husks in the sample you test. This can give a wrong result (I did this wrong for years and years!)

2. My understanding is that any colour change at all indicates conversion is not complete. If it is still like that after a couple of hours then suspect your temperature or your mixing.

Probably also worth mentioning that I no longer do the iodine test at all. I just check the temperatures and trust that the mash has worked. Lazy, but I seem to get away with it.

[gnorwebthgimi]

I haven't tried iodine tests for brewing but I remember them from school.

From what I remember:

A little bit of starch will go DEEP blue with ease and you NEVER got a clean yellow colour unless you dropped it in deionised water.

There is a lot of colour and other ions etc in the wort/mash and this is no doubt the reason you get green.

You could run a control test by putting a small piece of potato in a pit glass of water and giving it a stir, then add a drop of iodine and you will see it go a lighter blue (unless your use a particularly bad potato). See how little potato you need before you get a result.

[steve_flack]

A little bit of starch will go DEEP blue with ease and you NEVER got a clean yellow colour unless you dropped it in deionised water.

Sorry to disappoint you but I always get a yellow colour when I do it the way I described. As mentioned above, if you have any grain material in there it will not give you yellow. I recirculate my mash so the wort is very clear and I take just the liquid.

[gnorwebthgimi]

NP Steve

School Iodine probably wasn't all that great and I'm remembering back long ago.

[beer gut]

thanx for the reply everyone i think i have just noticed where i might have been going wrong when i test with iodine i tested with grain husks with the wort test i thought you would have to test both husks and the wort.