Iodine starch conversion on wheat beers

I was trying a decoction mash on a wheat beer earlier this week and so decided to do an iodine starch conversion test, just to see how things were going. I never really got full conversion despite some nice long alpha and beta rests.

Has anyone else had this problem? Is this typical for wheat beers?

FYI I used 50% pilsener and 50% wheat malt in the mash.

Beer tastes good about 1/2 the way down to where I hope it will finish.

I don't know about decoction; but I always do an iodine test and my last Brew in Bag Wit beer with 50% Pilsner malt and 50% white wheat passed the iodine test after 70 minutes. I did, however, do a protien rest at 125F for 15 minutes. This should always be done with high adjuncts such as wheat.

My guess is something went wrong in the mash; all starches should have been converted.

Again, I've never done a decoction.

The wheat beers I decoct provide a slight positive reading on the iodine test. This is probably a false positive because those beers tend to have a lot of small grain particles in suspension, at least more than in my all-barley brews. My theory is that the wheat breaks down more readily than barley when decocting, leaving more bits of it floating around.

If you were using unmalted wheat, I'd say you may have denatured some of your enzymes and that may have impeded starch conversion, but wheat malt should have more than enough DP.

The past few times I made a wheat beer, I used approximately 50% wheat malt and didn't have a problem with conversion after 60 minutes.

I happened on this yesterday while reading Jim Liddil's lambic page:

"Lambic is made by what many consider an anachronistic process. The grist is made up of 30-40% raw unmalted wheat with the remainder being malted barley. The mashing process is carried out using a technique called turbid mashing. Unlike decoction mashing the liquid portion of the mash is removed and boiled, leading to poor conversion and large amounts of unconverted starch ending up in the finished wort."

Perhaps boiling some of the liquid portion of the mash with the decoction will fix the starch, leading to less conversion? For the record I used malted wheat, though.

Either way, the beer is attenuating nicely right now. Checked yesterday, still a nice Krausen going and the gravity is down from 1.050 to 1.018.

I appreciate everyone's thoughts!

I'm ending a 120 minute mash with 40% wheat. It took a very long time, obviously, to convert with an iodine test. I had to decoct 2 gallons just to keep in my target mash temp. Which was 148°f for this particular beer.

I think much of your problem with conversion on wheat is due to the nature of the wheat kernel. Wheat is smaller and harder than barley so you often get a poorer crush on wheat. That poorer crush means that it takes longer for the wheat particles to wet through which in turn leads to slower conversion. Try double crushing the wheat or crush with a tighter setting on the mill. You may need to add rice hulls to keep from clogging the screen on the mash tun or better yet, use a bag like a paint strainer bag to filter out the small wheat particles.

RM-MN said:

I think much of your problem with conversion on wheat is due to the nature of the wheat kernel. Wheat is smaller and harder than barley so you often get a poorer crush on wheat. That poorer crush means that it takes longer for the wheat particles to wet through which in turn leads to slower conversion. Try double crushing the wheat or crush with a tighter setting on the mill. You may need to add rice hulls to keep from clogging the screen on the mash tun or better yet, use a bag like a paint strainer bag to filter out the small wheat particles.

Click to expand...

I think you're right about that. I didn't really reach 100% conversion even after 120 minutes and two decoctions to keep the temp up. Double crushing the wheat malt is certainly the best bet and I will be doing that for now on.