Iodine test?

[bhabermann]

Hello. I'm curious as to why mash time is about an hour? I'm brewing right now and 15 minutes in we did the iodine test and it cleared up which in my reading means the starches have converted to sugar or something right? Do we still need to wait?

 

[day_trippr]

Pretty amazing, isn't it? The highly modified base grains we use these days are almost magical wrt conversion time.

But, even after countless batches that showed complete conversion in 20 minutes or less, I still do 60 minute mashes - and just totally skip conversion testing. As it turns out I use the time for other brew day functions - and catching up with HBT

Cheers!

 

[stz]

I used to test, but stopped when I realised I always had complete conversation in 20 minutes. Modern fully modified grains have diastatic power to spare and as long as you are stick to at least 60% can't foresee problems. I too always wait out the 60 minutes because other things are happening in there and I couldn't tell you if they are done or not. I use the time to circulate sanitiser through my kettle, pump, plate chiller and fermenters while humming the circle of life.

 

[nasty_rabbit]

I'm sure that 60 min. is just a rule of thumb schedule. Using an iodine test is (in my opinion) the more accurate method for checking conversion. I made a cream ale awhile while back that I mashed at a lower temperature than normal (148f) and it was scheduled for 90 minutes. Iodine testing the mash, it took closer to 120 minutes for full conversion. Yes I've tested and it has ranged from 30 to 90 minutes depending on temperature so now I don't use a clock but do use a pipette.

 

[Silver_Is_Money]

I'm willing to speculate that even if your iodine test shows conversion complete at 20 min., your mash efficiency will be somewhat higher if you give it 60 min., and higher again for 90 min.

 

[Yooper]

The mash may be converted in 20 minutes, but even after conversion from starch to sugar, the enzymes still work to further break down the sugars to a more fermentable wort.

I can't find a free resource link at the moment, but recommend reading Malt and Mashing by Briggs, if you can find it. I think it's been out of print for a long time.

 

[nasty_rabbit]

Fair enough. I'm not going to dispute science nor Yooper.

 

[Cyclman]

http://braukaiser.com/blog/page/7/

 

[doug293cz]

The iodine test is problematic for a couple of reasons.

1. Many instructions recommend excluding grits from the sample. This is wrong! Starch converts to dextrins and smaller sugars extremely fast in the wort. But, there can still be strach left in the grits. You need to sample grits, and crush them more, before adding the iodine.
2. A negative starch test only means there are no starches present, not that the dextrins have been minimized (I think @Yooper mentioned this first.)

A better test for mash completion is monitoring the SG of the wort in the mash. When the SG stops increasing with time, your mash is done. This makes sure you have gotten all the available starch out of the grain. Then conversion of dextrins to fermentable sugars will complete during lautering. Also, if you know the SG of the wort in your mash, you can calculate your conversion efficiency using the method here.

Brew on

 

[Gerry_P]

if you have a thermometer, you don't need iodine.

Feel free to quote me on that.

 

[RM-MN]

Hello. I'm curious as to why mash time is about an hour? I'm brewing right now and 15 minutes in we did the iodine test and it cleared up which in my reading means the starches have converted to sugar or something right? Do we still need to wait?

Yes you need to wait for a couple reasons. If you included grains in the sample and got no response from the iodine your conversion is complete. If you didn't include grains you don't really know.

The other reason is the extraction of flavors. I've done a 10 minute mash and got full conversion, the beer attenuated well which indicates that the mixture of fermentable and unfermentable sugars was close to correct but the beer was flavorless. Extending the mash to 20 minutes on the next batch got me essentially the same attenuation but a much better tasting beer. I now advocate a mash no shorter than 30 minutes to make sure your beer has decent flavor.

 

[bhabermann]

Thanks everyone. We waited the full 60.