Poor starch conversion?

[Captain Damage]

Sorry, this is gonna be a bit long, but I’m looking for some expert advice/critique.

I normally do partial mashes. Last week I did my first all-grain brew, an ordinary bitter BIAB, but my iodine tests seemed to show that I never achieved full starch conversion (saccharification). I read (somewhere) that getting particulates in the test sample could cause a false negative, and although I was careful to get clean samples I hoped that was the issue and went ahead with the brew. After the boil, the wort in the fermenter was some of the clearest I’ve ever made, so I’m confident that I didn’t boil a bunch of starch and make beer-gravy, but I still have questions.

Recipe and process:
OG: 1.037 FG(est): 1.009 IBU: 29.8
5lbs Maris Otter
8oz crystal 40
2oz victory
9oz sucrose (late addition)
1.5oz fuggle aa4.0 60 min
1.5oz fuggle aa4.0 10 min
Optional - 0.5oz EKG dryhop 5 days.
Wyeast 1335
Mash 60 mins at 154F

The MO was crushed at my LHBS, I crushed the crystal and victory myself in my burr coffee mill at the widest gap setting - I’ve done it before for small amounts, never had a problem. Paint straining bag went in my 5 gallon cooler, grain went in the bag with a handfull of rice hulls. I stirred the dry grain up well.

I poured in 7 quarts of 171F water into the cooler and stirred up the mash. The temperature was a little below my target, so I ladled in some 200F water, about 8-10 oz total, until the temperature got to 154F. Put the lid on the cooler and let it sit. After 20 minutes I stirred the mash and did an iodine test, which came up negative. Let the mash sit another 20 mins, stirred and check conversion, still negative. I stirred some more, hoping I could “help” it, and let it sit again for 10 mins, by this time the temperature had dropped to 150F. Stir, check, still negative. Left it for the last 10 minutes. The wort was very sweet, as I would normally expect.

Mashed out with 3.75 quarts of 200F water, let it sit for 10 minutes. Pulled the grain bag out of the cooler and squeezed the hell out of it to get all the good stuff. Then the wort went into my kettle. Since I simply don’t have the capacity to do full boils at this time, I did this as an all-grain partial-boil, which I know is unconventional, but it’s what I can do right now. The boil and cooling proceeded normally, and I hit the estimated gravity, 1.037, exactly.

Now a week later, the beer looks good, tastes good, and I’ve got a gravity of 1.010 - that’s close enough to the estimate I’m okay with it. I’ll let it sit in primary another two weeks, it may or may not lose that last gravity point, but I’m not concerned about it.

Are there any obvious problems with my procedure? I get my temperatures and numbers from BeerSmith. All of the water I brew with is carbon-filtered (Pur tap filter). I’ve never tested or adjusted the pH, or added any minerals or other water treatments. Should I?

Or should I just assume the iodine tests were wrong somehow? Is there a trick to doing them correctly? I took a spoonful of liquid from the wort and a drop of iodine in the spoon. Usually this shows me conversion by a half hour or so into the mash.

Any input is greatly appreciated!

 

[Yooper]

I put my wort on a white plate, and then use a toothpick to drop in some iodine and streak it across the wort.

Yours actually turned black the entire time?

 

[Northcalais40]

An hour isn't an outrageously long mash. An iodine reaction doesn't surprise me.

 

[Captain Damage]

I put my wort on a white plate, and then use a toothpick to drop in some iodine and streak it across the wort.

Yours actually turned black the entire time?

Black every time. And quickly, too. Even at the end of the mash it took a second or less to turn. I use a white plastic spoon, rinse it well between tests.

 

[boo boo]

Black every time. And quickly, too. Even at the end of the mash it took a second or less to turn. I use a white plastic spoon, rinse it well between tests.

Squeezing the bag only will let in tannins from the husk into your brew, and it might get miniscule husk particles into the sample turning the test black. As long as you got your gravity I wouldn't worry about it.
I have given up on doing the test. My wort always turns out fine.

 

[Yooper]

Black every time. And quickly, too. Even at the end of the mash it took a second or less to turn. I use a white plastic spoon, rinse it well between tests.

I assumed that you were doing that, but I wanted to confirm. With a mash temp of 154 or above, the mash should convert within 30 minutes.

Next question- how accurate is your thermometer?

 

[devilishprune]

Does it fail the iodine test now? If they were present after the mash they should still be there right?

Are you checking gravity of your first runnings to determine the amount of conversion that you're getting during the mash?

 

[Captain Damage]

Next question- how accurate is your thermometer?

My thermometer was accurate until it fell in the ice bath while cooling the wort. Time for a new one.

Does it fail the iodine test now? If they were present after the mash they should still be there right?

I didn't think to test the wort after the boil. Testing the beer as it is now shows no starch.

Are you checking gravity of your first runnings to determine the amount of conversion that you're getting during the mash?

I have not been checking the gravity during or after the mash. Only after the boil.

I'm not worried about this beer, having seen/tasted that it's coming along well. I was more concerned that there might be something clearly wrong with my process. I'm the only one among my brewing friends doing any mashing and I was worried I'd have to turn in my expert card . Since no one has come up with an "Are you nuts? Don't do that!" my only real concern at this point is the reliability of the iodine test and my ability to gain accurate data from it.

 

[Northcalais40]

Braukaiser.com has a chart that lists the gravity of first runnings for a wide spread of strike water to grist ratios. An example, you mash in at 1.24 qts/lb the og of the first running should be 1.096 if your converted. I copied that chart to my brew calculator so I can cross reference on brew day.

You may be better served by figuring your brewhouse efficiency, as long as it's acceptable and consistent over several brew days, just keep your procedure consistent and keep good notes.

You already know more brewing science than most brewers from the medieval days, and they were the most popular guys in town.