Imperial Stout low ABV outcome

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Django-Parker

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Hello all, I've had back luck with two batches of an imperial stout with everything the same. It's not bad, but the abv for the 19 lbs came out to 6.5% abv. I was shooting for 9% or so. It's strange to me, since my previous batch before was an oktoberfest-like ale shooting for 5-6%, but turned out 7.2%.
I'll let you know my grain bill, mashing, sparging and everything else:

15 lbs maris otter
1 lb roasted barley
1 lb chocolate
1.3 lbs 60 L crystal
1 lb rolled oats

We use a bayou classic mash tun that is 10 gallons, but unfortunately has a 2 gallon false bottom. We put 7.5 gallons of water, then the grain.

Ph was 5.6

Mash temperatures stirring every 5-10 minutes:
112 for 15 minutes
149 for 20 minutes
156 for 60 minutes
added 1lb of Rice Hulls because it would be too thick for the regular mash.
170 for 15 minutes - stirred alot at first, then let sit for the rest of the 12 minutes, so the grain bed is at rest.

vorlauf for 5-10 minutes
Fly sparged 1.5 gallons (190F) slowly, dripping 8" above into mash tun for 90 minutes. We collected 6.5 gallons.
Our temperature inside the mash tun dropped from 170 to 145 in this time frame. Unsure how to keep it constantly at 170... Though this is the same that we had for the Oktoberfest...

Boiled for 120 minutes and brought it down to a little under 5 gallons (4.8).
Specific gravity for first batch 1.076
Specific gravity for second batch 1.072

We were thinking of adding 1.5 lbs of rice hulls next time and using 2 gallons of sparge water, but we are absolutely unsure about why we aren't getting a higher OG/SG.

Thank you for reading all of this and helping. I appreciate your time. Thank you!
 
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BrewMan13

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Only thing that comes to mind is possibly your efficiency calculations. You're going to get worse efficiency on a big beer, so if you used your typical numbers this could maybe explain it. I typically get 10-15% worse efficiency on big beers compared to normal strength. For the record, my imperial has 22+lbs of grain and I got 1.100 last time. Though having said that, I feel that's not the whole story. Also, your pH was good, but not sure why the acid rest was needed with all that dark malt in there.
 

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Agreed, efficiency drops but you do seem oddly low. The additional sparge water and boiling longer for it should help get you about back to normal though.

1) Are the extra false bottoms using up a ton of water, leaving your mash fairly dry?
2) Grain crush - it has to be good, or you won't extract what you want from the insides. Unless you are doing it yourself you don't know what you'll get and even the shops can be off especially if people come in and adjust the rollers for any reason. That has really thrown me in the past, or at least I think that was it, ever since I bought my own crusher I've had super consistent results.
 

CascadesBrewer

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Ph was 5.6
At what point in your mash steps did you measure pH? Unless your water is pretty alkaline, 5.6 seems much higher than I would expect with that much roasted malts and crystal malts...plus and acid rest added to the mix. I am not convinced that mash pH has that much impact on efficiency most times, but it can if it gets too far out of line.
 

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Mash temperatures stirring every 5-10 minutes:
112 for 15 minutes
149 for 20 minutes
156 for 60 minutes
if you weren't stirring constantly as you stepped up the temperature you denatured a lot of the enzymes. Your mash has grains in it, not just water. When you start heating water it recirculates freely. Mashes do not.
 
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Django-Parker

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Only thing that comes to mind is possibly your efficiency calculations. You're going to get worse efficiency on a big beer, so if you used your typical numbers this could maybe explain it. I typically get 10-15% worse efficiency on big beers compared to normal strength. For the record, my imperial has 22+lbs of grain and I got 1.100 last time. Though having said that, I feel that's not the whole story. Also, your pH was good, but not sure why the acid rest was needed with all that dark malt in there.
I did the 112 rest, because of adding the oats. I thought it might help prevent a stuck sparge. I also added the rice hulls. It might not have been necessary, but with all that grain, I didn't want to chance it being stuck. Yeah, your OG was way more closer to what mine was in ratio. My efficiency calculations brought me to an estimated abv or 9-10%...
 
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Django-Parker

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Agreed, efficiency drops but you do seem oddly low. The additional sparge water and boiling longer for it should help get you about back to normal though.

1) Are the extra false bottoms using up a ton of water, leaving your mash fairly dry?
2) Grain crush - it has to be good, or you won't extract what you want from the insides. Unless you are doing it yourself you don't know what you'll get and even the shops can be off especially if people come in and adjust the rollers for any reason. That has really thrown me in the past, or at least I think that was it, ever since I bought my own crusher I've had super consistent results.
All of the spent grain at the end is fairly wet or at least moist. That's a great comment about the grain crush. I have been using the brew shop's grain crush. The brew shop that I use it, is also a brewery that makes a 13% imperial stout. I wonder if someone might have messed with it though... That's a good thought of investing into a grain crusher. We're looking to get a 20 gallon mash tun, so having our own bag of base malt and our own crusher might just be better. Thank you!
 

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There's a rule of thumb about 1.25 - 1.5 qts water per pound of grain. But that works for an open cooler or pot. If you have false bottom(s) taking up some of the space then that water volume has to be subtracted out.

Your grains should be under water when you mash. Well I guess I can't say that as an absolute thing, but - if they aren't submerged during the mash cycle with at least a little water on top then you are probably not using enough mash water to begin with.

Off the top it sounds like you have enough water, but - maybe not if those bottoms take up tons of space.
 
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Django-Parker

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At what point in your mash steps did you measure pH? Unless your water is pretty alkaline, 5.6 seems much higher than I would expect with that much roasted malts and crystal malts...plus and acid rest added to the mix. I am not convinced that mash pH has that much impact on efficiency most times, but it can if it gets too far out of line.
We measured the pH at the 149F temperature. We cooled it down to 70F and used a digital milwaukee 102 pro. We calibrate it each time we brew as well. I added 1/4 tsp of baking soda to get the pH a bit higher to 5.6. I saw Martin Brungard suggested getting a 5.5-5.6 pH for an imperial stout on a thread.

I tried to add as much information as I could, because as a relatively new brewer, it could be a myriad of things that could be wrong! Thank you.
 
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Django-Parker

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if you weren't stirring constantly as you stepped up the temperature you denatured a lot of the enzymes. Your mash has grains in it, not just water. When you start heating water it recirculates freely. Mashes do not.
We always stir quite a bit, especially when we step up the temperature with the burner. Someone who runs my local brew "guild" suggested to just do a single infusion; stir at the beginning and let it sit until it's done. He also said something seemingly against step mashes overall.

Others have suggested that stirring too frequently (not when stepping up) can cause heat loss and other potential problems.

I think we are going to get a thermapen to calibrate our temperature as well. Thank you!
 
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Django-Parker

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There's a rule of thumb about 1.25 - 1.5 qts water per pound of grain. But that works for an open cooler or pot. If you have false bottom(s) taking up some of the space then that water volume has to be subtracted out.

Your grains should be under water when you mash. Well I guess I can't say that as an absolute thing, but - if they aren't submerged during the mash cycle with at least a little water on top then you are probably not using enough mash water to begin with.

Off the top it sounds like you have enough water, but - maybe not if those bottoms take up tons of space.
Yeah, the grain was submerged by a few inches or maybe more. I try to get a good ratio with the 2 gallons subtracted, but with a big beer, it's a little more difficult. That's why I added the rice hulls right before mash out, otherwise stirring would be too much of a workout. Thank you!
 
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Django-Parker

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I'm guessing from more research and help from everyone that it might have to do with a temperature calibration issue (the internal probe is at one spot and might not be 100% accurate), stirring too often during rests and doing a step mash instead of single infusion. Also, to use an insulated blanket around the mash tun as it rests (with the flame off of course).

Otherwise, I'm still not sure about it. I'll try out these new methods. My sparge water was a little slower than the runoff, but I caught that and changed the speed, because the wort level above the grain bed went down for less than a minute to the grain bed level. Maybe that could have ruined the OG?

Any other suggestions? Thanks again everyone for your input and helping.
 

bracconiere

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what was your first runnings SG, and last? i just had a crap frosted flake brew...but being that i stopped the sparge, and it was still running at ~1.023, thinking i should have taken a bit more time with it, or boiled more off...
 
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Django-Parker

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what was your first runnings SG, and last? i just had a crap frosted flake brew...but being that i stopped the sparge, and it was still running at ~1.023, thinking i should have taken a bit more time with it, or boiled more off...
we didn't do a hydrometer reading during sparging, only before adding the yeast in the carboy, which was 1.072. I think that's we should probably get a refractometer. I could have added something similar to the maris otter in terms of dried malt extract before boiling.

Our FG was about 1.026. It tasted good, but just was disappointed with our extremely low efficiency for this beer. Sorry to hear about yours. Yeah, I think sometimes me not knowing the SG during the process gives me the "ignorance is bliss" and hopeful for an outcome, then only to be hit with a sad reality...
 

bracconiere

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i usually use something like this for mash samples....and temp correction. mostly for an idea, not necessarily accuracy, but it tells me when everything is done.....

brewing right now, first runnings were at 1.047 at 125f....let it ride longer, until it stopped going up...ended at 1.068 at 125f.....i'm no good brewer, but it usually works for me. :mug: (speaking of which, i think i'm sparging to fast, and need to take a sample! thanks!)

damn i forgot the link

 
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