Qs about conversion, batch-sparging

[Mohanbrau]

I'm a noob to partial-mash brewing, but have been extract brewing for 21 years, so I understand the theory thoroughly but I don't have any experience to fall back on.

Question #1:
I've done 3 partial-mash batches, using a 3-gallon Gott cooler, and achieved complete conversion with the first batch, but not the last two. I'm mashing from 3-6 lbs of fully modified pale or lightly kilned (Munich, Cara-pils) malt with 1.375 qts of water per pound of grist with a single-infusion at 152 deg F. On my last batch, for a maibock, I tested for saccharification with iodine after 30 minutes, 45 minutes, and 60 minutes. At 45 minutes, the temperature had dropped to 148, so I added .8 qts of boiling water to bring it back to 152.

Even after 60 minutes, the iodine still turned blue/black, although it was orange-ish around the edges. Any ideas about what I'm doing wrong and should be doing instead? Thinner mash? Higher mash temp? Since I was going to be using 8# of LME in the brewpot, I just went ahead and sparged.

I guess I should mention that I'm using a grain bag and batch sparging in the cooler. I can see where that might affect my extract efficiency, but not the actual conversion process, right? I'm very careful to poor my mash-in water into the bag and thorough stir my grist, so I'm confident I don't have pockets of dry grain that might be leaching starch into the liquor.

Which brings finally me to Question 2:
If anybody has any thoughts or experiences with batch sparging a partial mash to share, I'd like to hear them. The simplicity of not messing with a false bottom and stuck mashes and a hot liquor tank and sparge arms and sparging rates, the economy of not converting the cooler, the ease of clean-up with the grain bag, the advantages seem to go on and on. What's the downside? I can compensate for lower extract efficiency with a couple of dollars' worth of extra malt.

Sorry for the long-winded questions. Thanks in advance for any help anyone can offer.

 

[Northcalais40]

It can take upwards of 90 min for total conversion, so I don't think your doing any thing wrong. A low mash temp like 152F is also going to delay things. You could try a stepped mash like 150F for 30 min then infuse to hit 158F until completion. Though that is a lot more work. I would suggest mashing at 156F.

A lot of times an iodine test can be tough to judge. I may be wrong, but it seems like having particles of grain in the test makes a reaction, even when your very near full conversion. I put a few drops of wort on a tea plate and let it cool, then tip it so the clear liquid can run away from any grit to get a clear sample. I hope that makes sense.
Some folks use a piece of sidewalk chalk as a substrate for an iodine test. Check out Braukaiser.com.

If you have a cooler you can convert, slap a $5 braid on it and batch sparge. It is worth trying. The down side to BIAB vs no sparge in a cooler with a braid is that you need a bag. With a braid you can sparge, or do no sparge. basically the braid replaces the bag.
And you don't need a sparge arm, a tube will be just fine.

 

[Walker]

regarding your conversion test...

I had a batch one night where I thought conversion was not taking place, even after 90 minutes of perfectly held 150*F mash.

It turns out that my problem was that I was getting bits of husks in my sample and they were reacting with the iodine to cause it to turn black. If I took a sample of work and let it settle out so that I could get just the liquid and no chunks, then it showed that conversion was complete.

 

[Northcalais40]

It turns out that my problem was that I was getting bits of husks in my sample and they were reacting with the iodine to cause it to turn black. If I took a sample of work and let it settle out so that I could get just the liquid and no chunks, then it showed that conversion was complete.[/QUOTE]

I thought the same thing happened to me, but wasn't sure that it worked that way. Is there some starch in the husk that is not convertable?

 

[Mohanbrau]

Thanks for the quick responses. This is very helpful. I didn't let the sample cool, nor did I attempt to separate the grits from the liquid. I tasted a second sample, and it was unbelievably sweet, so I went ahead and sparged. Not the most scientific test, but my previous batch that also failed the iodine test turned out awesome, so I figured I was safe.

Thanks again for the help.