Low conversion - Where did I go wrong?

[Brak23]

Hey there,

I brewed this recipe on Saturday:
10 lbs Marris Otter
1 lbs Black Patent Malt
12 oz Roasted barley
12 oz Flaked barley
8 oz flaked oats
8 oz Crystal 120L
8 oz Cara Pils
8 oz Rice Hulls

I mashed the recipe at 156 degrees for 1 hour (recipe said 45 minutes, but I let it sit a touch longer). Then batch sparge with 168 degree water. I nailed my water numbers (mash 4.5 gallons, sparge in ~4 gal) and ended up with a pre-boil volume of 6.5 gallons. After an hour of boiling I got it down to 5.5 gallons, knowing the fermentation I will lose close to a half gallon.

Now, I am not an expert in all grain, and still very much learning. This was my third all grain recipe and I generally have gotten close to my OG number, but this time its showing its way off. It was estimating (using Beer smith) a 1.072 OG, and I got 1.035. Im using a calibrated refractometer right now, as my hydrometer broke the last time, but I can't imagine it being that far off. I do have a new hydrometer coming in the mail to be safe.

Anyway, ive never been this far off... I used iodine to test the mash sample (first time ive done this) and I got a nice red color, and no black in the iodine. Based on what I read, this is showing full conversion.

So im a bit perplexed as to how this could be so vastly off. Ive read numerous factors of temp, grain crush, volumes, etc, and I feel like I really hit everything right. The one thing I am not 100% on is that the grain I got crushed at a LHBS and used their mill. But so many people mill grain there, that I can't imagine that would be a massive problem.

Any thoughts, given what I was doing, where I can evaluate why my number is so far off?

 

[GQT]

You might be alright with your mash (I'm not saying you are, but there are chances). Refractometer is an optical device and correct refraction can be tampered with by many factors, such as temperature and micro particles in liquid. Many modern refractometers somehow compensate for temperature but when the liquid is all muddy the offset can be quite big.
So choosing which one to trust, I would trust the iodine test.

 

[Brak23]

You might be alright with your mash (I'm not saying you are, but there are chances). Refractometer is an optical device and correct refraction can be tampered with by many factors, such as temperature and micro particles in liquid. Many modern refractometers somehow compensate for temperature but when the liquid is all muddy the offset can be quite big.
So choosing which one to trust, I would trust the iodine test.

Thanks, its been driving me crazy that I have to trust a refractometer I havent used a ton of us. I saved some wort, pre-yeast and when my hydrometer comes, I can give that a test to see.

 

[kev211]

This may be a dumb question so forgive me if it is, but did you get the refractometer correction right? What was the brix reading?

 

[Brak23]

This may be a dumb question so forgive me if it is, but did you get the refractometer correction right? What was the brix reading?

I got a Brix reading of 9

 

[doug293cz]

Hey there,

I brewed this recipe on Saturday:
10 lbs Marris Otter
1 lbs Black Patent Malt
12 oz Roasted barley
12 oz Flaked barley
8 oz flaked oats
8 oz Crystal 120L
8 oz Cara Pils
8 oz Rice Hulls

I mashed the recipe at 156 degrees for 1 hour (recipe said 45 minutes, but I let it sit a touch longer). Then batch sparge with 168 degree water. I nailed my water numbers (mash 4.5 gallons, sparge in ~4 gal) and ended up with a pre-boil volume of 6.5 gallons. After an hour of boiling I got it down to 5.5 gallons, knowing the fermentation I will lose close to a half gallon.

Now, I am not an expert in all grain, and still very much learning. This was my third all grain recipe and I generally have gotten close to my OG number, but this time its showing its way off. It was estimating (using Beer smith) a 1.072 OG, and I got 1.035. Im using a calibrated refractometer right now, as my hydrometer broke the last time, but I can't imagine it being that far off. I do have a new hydrometer coming in the mail to be safe.

Anyway, ive never been this far off... I used iodine to test the mash sample (first time ive done this) and I got a nice red color, and no black in the iodine. Based on what I read, this is showing full conversion.

So im a bit perplexed as to how this could be so vastly off. Ive read numerous factors of temp, grain crush, volumes, etc, and I feel like I really hit everything right. The one thing I am not 100% on is that the grain I got crushed at a LHBS and used their mill. But so many people mill grain there, that I can't imagine that would be a massive problem.

Any thoughts, given what I was doing, where I can evaluate why my number is so far off?

Using my batch sparge simulator and your numbers, I get a maximum possible OG of 1.070, so BeerSmith seems a little high at 1.072. To get an OG of only 1.035, I had to drop the conversion efficiency to 47% - 48% (lauter efficiency is 77% - 78%.) That is about the lowest estimated conversion efficiency I have ever seen. Bad crush could be part of it, but is unlikely to explain all of the problem. One thing to check is the calibration of your thermometer. If it is way off, then your conversion could suffer.

Brew on

 

[kev211]

That's so strange. That's like 38% efficiency... Huh.

 

[doug293cz]

That's so strange. That's like 38% efficiency... Huh.

Yup.

Brew on

 

[BeardedBrews]

Safe bets are a bad refractometer calibration or 10# of Maris that didn't go through the mill.

If you're using a refractometer you can check the mash while it converts, just as a sanity check, and to give you a chance to make corrections with dme before the boil.

Let us know what you get on the hydrometer.

 

[Brak23]

Got hydrometer, confirmed that my refractometer is actually 100% spot on. So I somehow ended up with 1.035.

I checked my thermometer that I used and it was off. It kept reading a lot higher than the actual temp. So that probably explains it. Though, that would mean my temps were running hot, I still got conversion in my mash (confirmed with iodine), but ive never really mashed too hot to know what it actually does to the sugars and starches.

 

[doug293cz]

Got hydrometer, confirmed that my refractometer is actually 100% spot on. So I somehow ended up with 1.035.

I checked my thermometer that I used and it was off. It kept reading a lot higher than the actual temp. So that probably explains it. Though, that would mean my temps were running hot, I still got conversion in my mash (confirmed with iodine), but ive never really mashed too hot to know what it actually does to the sugars and starches.

If the thermometer reads higher than actual temp, then you would have mashed at lower than intended temp (think about it.)

Brew on

 

[Brak23]

If the thermometer reads higher than actual temp, then you would have mashed at lower than intended temp (think about it.)

Brew on

Oh good lord, im dumb. Long day at work, brain dont work good

Anyway, if I mashed too low, how would the iodine show any sugar conversion? I would expect it to flash black with the presence of starches. Just trying to make sure I understand if I am reading iodine correctly.

 

[doug293cz]

Oh good lord, im dumb. Long day at work, brain dont work good

Anyway, if I mashed too low, how would the iodine show any sugar conversion? I would expect it to flash black with the presence of starches. Just trying to make sure I understand if I am reading iodine correctly.

The mash temp may have been too low to get much starch gelatinization. So you would have very little soluble starch in the wort, and what was there could convert pretty quickly. A good iodine test would also sample some of the grits, and the grits should be crushed more as part of the test.

Edit: A better, quantitative, way to measure conversion is to take SG readings of the wort in the mash and compare to the value in the table here for your mash thickness.

Brew on