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10% Less Mash Efficiency Between Brews

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slurms

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Two weeks ago I brewed a brown ale (5.5 gallon) and hit all my numbers dead on (within reason). Mashed for 60 minutes and calculated a mash efficiency at 82% (OG of 1.064). Great. Today I brewed a wheat beer (4.0 gallon), mashed for 90 minutes and got a mash efficiency of 72% (OG of 1.050)! I'm a bit stumped as to why it's such a big difference.

My process was the same between the two: BIAB no sparge, same crush, used an Igloo cooler for mashing (joys of brewing in upstate NY in the winter), same water, same rest temperature, similar additions to make mash pH ~5.4 (per Bru'nWater, don't have a pH meter). Stirred and checked temperature of the mash every 15 minutes. Refractometer seems to be calibrated correctly.

The only difference that I see between the two (other than the mash time) is the volume in the mash tun. With the 5.5 gallon brown ale, that thing was pretty full and dropped maybe 2F. The 4.0 gallon wheat beer filled maybe 3/4 of the way and definitely lost more than 2F over the course of the 90 minutes.

Now, how can it be that the bigger (gravity-wise) beer which mashed at 60 minutes have a better efficiency than a smaller beer which mashed at 90 minutes? Anyone have any idea what went on here? Kinda bummed about it since the last brew went so well...
 

VikeMan

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Did you measure your preboil and/or post boil volumes before you computed your mash efficiencies?
 
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Yes, see below.

I know there is some discrepancy between volume/SG from pre/post boil. I think that has something to do with using a refractometer (but doesn't account for the large differences I'm seeing). Also, while the volumes were measured at temperature, the ones below were adjusted to 70F. Using a SS ruler to measure water height plugged into a curve fit I made for my kettle.

FYI, am calculating efficiency by [(SG_preBoil-1)*1000*V_preBoil]/SG_Points (i.e., points extracted divided by theoretical points).


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VikeMan

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The only other thing that comes to mind is the theoretical points. i.e. possible differences between real and assumed PPG potentials of the grains in at least one of the grain bills.
 

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I get the logic of the lower temp raising the efficiency, all else being equal, I think you make sense there, if you wondered.

What did you use to calculate efficiency? Maybe something wasn't loaded correctly.

I want to say wheat is a good base malt and unlike say black patent has a similar potential (probably not the right word) as 2-row for example. But what about the rest of the grain bill, maybe other grains added were a lot different between batches?
 
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slurms

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I get the logic of the lower temp raising the efficiency, all else being equal, I think you make sense there, if you wondered
Both were at the same starting mash temp of 150F. The AmWheat lost more heat earlier on, and was at 148F at 30 minutes in, and ended the 90 minute mash at 146ish. Could be the lower temperature didn't help the cause.

Here's the grain bills for the two beers, with the assumed PPG for the grains.

Brown Ale
70% 2-Row (37 ppg)
16.5% Munich (33)
10% Special B (34)
3.5% Chocolate (29)

AmericanWheat
60% White Wheat (40)
40% 2-Row (37)

Looking at the PPG for white wheat, it seems a bit high. Looks like BrewCipher uses 38 (though I use that and my own spreadsheets when making a recipe and for brew day for a side-to-side comparison).
 
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Yep. There's definitely something else at play here, but that accounts for some of it for sure.
 

VikeMan

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Oh, yeah... you said "same crush." Meaning same mill gap? Wheat malt kernels are smaller than typical barley malt kernels. A mill gap that's good for barley is sometimes to wide for wheat malt, resulting in too coarse a crush.
 
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Hmm, good point. I didn't think of that. Yes, I meant same mill gap. I have it set to the smallest it can go (0.025") for BIAB use. I would imagine that would be good for the wheat, but maybe a double milling should have been in order to make sure the wheat was milled appropriately.
 

day_trippr

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fwiw, I run white wheat malt through an .025" gap, so I'm inclined to believe that's not the issue...

Cheers!
 

VikeMan

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channeling due to the high wheat content? not as much husk to even out the wheat mash? just a thought...
OP said no-sparge. So channeling wouldn't matter, unless there are actually pockets of wort being left in the grain bag.
 

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still there would be a lot less husk in a 60/40 wheat barley mash.....
Wheat, even malted, is also more sticky, gooey. Chances are, without a sparge, more (high gravity) wort remained trapped in the grist. Next time, when doing wheats and such, hold 1-2 gallons of strike water behind for some dunk sparging. Measure the gravity of the sparge and see if it makes a difference.

The 0.025" mill gap should be tight enough to crush wheat malt well. Mine is set at around that for milling wheat and rye, with no efficiency issues. Oat malt is milled even tighter.
 

VikeMan

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Wheat, even malted, is also more sticky, gooey. Chances are, without a sparge, more (high gravity) wort remained trapped in the grist.
Could be, but I get the impression that he hit the volumes he was expecting. If so, that would imply that the grains didn't trap more wort than expected.
 

day_trippr

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lmao! Yeah, I get that a low-efficiency method would not be in your wheelhouse :D

Cheers!
 

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We assume you used (white) wheat malt, and not (unmalted) flaked white wheat. Is that correct?

What were the mash temps after 30'? 60'? If it dropped below 150F that can be part of the issue, not enough conversion.
 

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Hmm, good point. I didn't think of that. Yes, I meant same mill gap. I have it set to the smallest it can go (0.025") for BIAB use. I would imagine that would be good for the wheat, but maybe a double milling should have been in order to make sure the wheat was milled appropriately.
Wheat is not only smaller than barley (and that size can vary from year to year depending on growing conditions) it is also harder. While you have teh mill set for fine milling it is possible (likely) that the wheat wasn't crushed nearly as well as you would think and running it through twice at too big of a gap might not help a lot. If you plan to do a lot of wheat (or rye) beers, get a mill that can really chew it up like a Corona style. They aren't real expensive and can really improve the milling of wheat and rye.

The since you are doing BIAB, run all the grain through the Corona mill with it set tight. It works well for BIAB.

lmao! Yeah, I get that a low-efficiency method would not be in your wheelhouse :D

Cheers!
Don't count on BIAB no sparge to be low efficiency. My first couple got me 80% efficiency. I now do a sparge to volume as I use too small of a kettle for the beers I want to make and have never been that low since.
 
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Yep, this was white wheat malt. Single crushed through 0.025. thinking double crushing it next time would help, or better yet, the corona mill.

The mash temp started out at 150F at the start. 30 mins in it dropped to 148-149. After 60 mins it was 147-148.

I hit my anticipated preboil volume. My calculated grain absorbtion was a little more this time, but I also didn't, uhh, squeeze my bag as much.

A small amount of sparge water with this one sounds like it was almost needed because of the "gooey-ness" of the wheat malt. I'll keep that in mind next time I make a similar recipe with BIAB.

Thanks everyone!
 

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Yep, this was white wheat malt. Single crushed through 0.025. thinking double crushing it next time would help
Double crushing wheat on 0.025", yes, try that. And a (small) sparge.

I usually mill Barley at 0.034" and wheat, rye and other small kernel grain separately, at 0.025". So yeah, I usually need to reset the mill at least once every brew session. Oat malt gets crushed separately too, even tighter than wheat and rye. I'm guessing at around 0.016-0.018".

30 mins in it dropped to 148-149. After 60 mins it was 147-148.
Those temps (and time) should give you good conversion.
Do you stir a few more times during the mash? That too could help getting better, more thorough conversion, especially with sticky mashes.

That said I still think the sticky mash left more sugars behind, trapped in the gluey grist.
 
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I'm guessing at around 0.016-0.018
That's a pretty tight gap. Is that what you're guessing a corona mill puts out?

Yes, I was stirring every 15 mins. Probably one source of heat loss. My guess is the efficiency drop was based on poor crush size of the wheat and the gooey mash holding more of the sugars in. I bet my next batch will be up near 80% again, which has been fairly consistent up until this brew.
 

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That's a pretty tight gap. Is that what you're guessing a corona mill puts out?
A Corona mill is basically a corn grinder, it pulverizes corn kernels into fine grits. You can adjust them to mill coarser, more suitable for grain and our mashes. Trial and error. I don't see need for one if you have decent 2- or 3-roller mill and a strong enough motor/drill.

I have a Monster Mill (MM2) powered by a Harbor Freight Heavy Duty Low Speed drill. It has no trouble milling wheat malt at 0.025" gap, but you can hear the motor groan, doing the work. Pretty much any roller mill should be able to mill wheat finely enough on a single pass, as long as the rollers/gap stays put! Maybe check the gap afterward to make sure it didn't widen up.*

I get good conversion and mash efficiency (~80-85%), but I don't do full volume mashes. I mash with about half the water, and batch sparge twice, in equal volumes, with the rest. Especially with sticky grists, good stirring and sparging is part of the job. You should see a 50% rye mash, it's like a tun with cement, the wort coming out is like elmers glue! Stir often and hard to make it more fluid.

* There is only one correct way to set the gap on a roller mill, and lock it:
When adjusting the free roller it should come in from underneath and toward the driven roller, on both sides, left and right. When the gap is what you want it to be, lock both set screws. I give them a slight extra nudge with some pliers so they won't come loose. I also put some grease in the set screw threads and the corresponding threads in the mill cheeks, to reduce wear.
 
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