idodine Iodine Test

[ryankf]

Hello all,

Looking for feedback on experience doing iodine test on grain-in mashes. Have read the husk can cause false positive. Having used recommended dosage, temp ranges, and hold time and still not getting negative starch test results (using commercial enzymes). I use a hammer mill with 1/16th screen. Have considered taking a sample and essentially sparging or rinsing it through a fine screen (coffee filter) and doing starch test on the run off. Photo is of cooled sample after 2 hours rest at 135F with glucoamylase. Still very dark purple.

[jeffw]

Run the mash through a coffee filter to remove the solids and you should be good to go.

[Skaalvenn]

You need a clean sample of liquid, any solids (which I see there are quite a bit) will give a false negative.  You'll need to let it sit for a few minutes and then just barely skim the surface to collect a couple drops of mash. I prefer to use an eyedropper to grab mash samples when I do a test (which is rare, I know my process and enzymes are working).

Is your S/G or Brix where you expect it? 

 

[Huffy2k]

We use a paddle to stir the mash and then let the liquid drip from the end of the paddle into a dish. We can usually get a pretty grain free sample that way. 

[ryankf]

Thanks for the tips everyone. I'm sure the solids were the issue. I just did another test at 2 hour rest filtered through coffee filter and got a dark maroon or brown color. Not purple or blue. I've read that red/maroon/brown means starch is saccharified, but I was thinking it'd be lighter like the color of thinned out iodine, or pale. Perhaps not?

Starting Brix: 20

Ending Brix: we shall see - doing a longer gluco hold than normal to see if i can get it to go lower. in the past i've been getting about 12 point drop. Trying to troubleshoot lower than desired ABV.

[Blockader]

If your refractometer is reading 20 brix before fermentation and 8 brix after fermentation, than that is about right for full attenuation.

[ryankf]

1 hour ago, Blockader said:

If your refractometer is reading 20 brix before fermentation and 8 brix after fermentation, than that is about right for full attenuation.

Thanks Blockader. So I shouldn't be shooting for zero (0) on final Brix reading to reach attenuation? Is that due to the alcohol being present in the ferment and skewing the refractometer?

[Blockader]

That's correct. Strain out enough liquid to do a gravity reading with a hydrometer once fermentation stops. Than compare that reading, hopefully 1.00 or a little below, with what your refractometer reads, likely around 8 with a starting Brix of 20. As long as you keep the same starting gravity you will have confirmed your ending brix and can use the refractometer for future final gravity readings.