Imperial Stout Fermentation Issues

[jameslg2169]

I've been home brewing for about 4 years now and I haven't run into too many issues with attenuation (fortunately), but I recently brewed 2 imperial stouts. The first did not attenuate as much as I wanted so I reformulated for additional base malt to be added, thinking that I may have had too much dark malts.

Anyway... on the second batch, brewed an American Porter right before the Stout and pitched on the yeast cake whichh was WLP090 and I made a starter of WLP099 to pitch about a week into fermentation.

On the stout, I hit an OG of 1.111, oxygenated the cool wort with pure O2 for about 90 seconds. The fermentation got down to 1.030... I was hoping for about 1.020. Just hoping you might take a look at my recipe and see if there's something blatantly obvious that I am missing.

Maris Otter: 78.8%
Munich: 8.8%
Crystal 120: 2.5%
Chocolate: 4%
Roasted Barley: 2%
Special B: 3%
Belgian Sugar: 3%

Estimated Beer Stats:
OG: 1.111
FG: 1.020
IBU: 60
SRM: 47

Actual Beer Stats:
OG: 1.111
FG: 1.030
IBU: 60
SRM: 47


Belgian sugar is probably not to style, but I wanted to add a little darker color to the beer while giving it fermentable sugars.

Any feedback is welcome!

 

[eluterio]

Mash temp? maybe change the yeast strain?

 

[jameslg2169]

Mash temp was 152-153... I figured the WLP099 would have chewed up anything thrown at it.

 

[eluterio]

What was your porter gravity?

 

[eluterio]

This is apparently is bugging me. Could this be because of yeast health? The Porter you brewed was too high of a gravity and when you put the IS on it the yeast was not healthy enough?

 

[jameslg2169]

Porter gravity was 1.075... ended at 1.017, which was 3pts higher than expected, but not 10-12. Porter sat in primary for about 17-18 days before being moved to kegs to sit for another month.

This was a 20 gallon batch of each.

I used 2 WLP090 packs, each with their own 2L 1.060 starter.

I used 2 WLP099 packs each with their own 2L starter of 1.111 (I didn't feel like mathing and figuring out what the OG change would have been with the starter addition).

 

[eluterio]

This is a tough one, so you used the yeast cake and you grew a starter for the 20 gallon batch?

Im still thinking it's a yeast health issue. Your grain bill and mash temp in any other batch of lower gravity beer would be just fine.

How does it taste??

 

[blizz81]

Obviously it gets tougher to hit normal attenuation targets as you start getting around that level of starting gravity...and any amount of specialty grains will make that harder, which you generally find in a stout (and do here to the tune of 11%). Sounds like you have tried to put in place a couple practices to get the most out of the yeast. I would probably suggest mashing low for a big guy like this. I've also seen other folks hit with another dose of O2 in the first 12-24hrs of ferm to help. Maybe would have added the sugar with the 099.


Though really I think 1.111 to 1.030 in an imperial stout is still doing pretty good, and likely will taste just fine to style.

 

[jameslg2169]

I actually set aside 5 gallons of the imperial stout and added 4.5 lbs of dextrose to it... so OG on that would be 1.159.... It's gotten down to 1.050 and stalled.

When I take the yeast cake from the other 15 gallons, I might just pitch that into the monster batch and see if it does anything.... If it doesn't, ah well... Still got 15 gallons!

It tastes a little on the sweet side... That's why I wanted to get another 5-10 pts out of it. I'm sure it'll be drinkable in 6 months or so, but I just wanted to make a 12% stout... cuz why not? hahaha

 

[jameslg2169]

Just in case you wanted to see what a 37.5 gal mash tun looks like with about 100 lbs of grain in it looks like on a homebrew system... lol

 

[solbes]

First of all a 1.111 OG stout is probably not going to get down to 1.020. Maybe its been done before, but I would find that unlikely in most fermentations. I think you can always add in fresh yeasties willing to go to battle to chew through another 5-10 points. A 1.5-2L starter pitched a few hours past peak krausen when they are at perfect health might work (it did for my first RIS).

Even pitching on a whole cake of yeast can only take it so far. Guess I would have expected 1.025 FG based on your grain bill, mash temps, the yeast pitch, and the pure O2. You're not that far off. Should be tasty!

 

[eluterio]

Just in case you wanted to see what a 37.5 gal mash tun looks like with about 100 lbs of grain in it looks like on a homebrew system... lol

holy jebus that thing is full!!! Throw some brett into it that could chew up the rest!!! JK man good luck sounds like your on your way.

 

[jameslg2169]

holy jebus that thing is full!!! Throw some brett into it that could chew up the rest!!! JK man good luck sounds like your on your way.

Yea, I wanted to max out my system just to see what I could do... had a water to grain ratio of 1.2... I could probably lower it to 1 and fit in another couple of lbs

 

[jameslg2169]

First of all a 1.111 OG stout is probably not going to get down to 1.020. Maybe its been done before, but I would find that unlikely in most fermentations. I think you can always add in fresh yeasties willing to go to battle to chew through another 5-10 points. A 1.5-2L starter pitched a few hours past peak krausen when they are at perfect health might work (it did for my first RIS).

Even pitching on a whole cake of yeast can only take it so far. Guess I would have expected 1.025 FG based on your grain bill, mash temps, the yeast pitch, and the pure O2. You're not that far off. Should be tasty!

I had actually pitched the WLP099 when it was around 1.040 and it only got down to 1.030... Ah well... doesn't seem like I did anything obviously wrong... controlled fermentation at 67 for about 2 weeks and raised it to about 70-71... Kinda kicking a dead horse at this point.... haha

 

[mrdauber64]

1.030 is an appropriate final gravity for an RIS, especially with that high of a starting gravity. I just read an article in BYO where they said Dark Lord finishes at 1.070, so even commercial example finish high. This style should be big, heavy and thick. 1.030 shouldn't be too sweet based on where you started.

The recipe looks good, I personally like the addition of the sugar. I put d-180 in all of my RIS. For lower attenuation mash at 149, that should get you to 1.20 ish. 1.030 is perfect in my opinion though

 

[jameslg2169]

1.030 is an appropriate final gravity for an RIS, especially with that high of a starting gravity. I just read an article in BYO where they said Dark Lord finishes at 1.070, so even commercial example finish high. This style should be big, heavy and thick. 1.030 shouldn't be too sweet based on where you started.

The recipe looks good, I personally like the addition of the sugar. I put d-180 in all of my RIS. For lower attenuation mash at 149, that should get you to 1.20 ish. 1.030 is perfect in my opinion though

I had 3 lbs of it hanging around... figured "hell, why not?"... haha... It's been in primary for about a month now and I'll probably keg it soon and let it age for 3-6 months and see how it turns out.... I'll update when it's finally done!

 

[specharka]

Dude, you are good. Almost 75% attenuation on a RIS and you're in 10+% ABV territory. Let it age for at least six months and see how you feel. Booze is great, but the complex sugars are what make a RIS so special.

I recently brewed a RIS and got it to 1.022 from 1.092...and I was ecstatic to get there. I would have been worried about infection if it finished lower than that.

 

[jameslg2169]

Finally racked 15 gallons to kegs. Ended up at 1.029. 10.9%... I pitched the yeast cake from those on the one that I'm trying to get to 20% and it's bubbling again... Smells and tastes good from the sample I've taken!

 

[blizz81]

Finally racked 15 gallons to kegs. Ended up at 1.029. 10.9%... I pitched the yeast cake from those on the one that I'm trying to get to 20% and it's bubbling again... Smells and tastes good from the sample I've taken!

Now throw 10oz of bourbon + 6oz of oak at one of the kegs!

 

[dtwhite]

I'll just chime in with the same things everyone else said:

1) That's pretty good apparent attenuation even at 1.03
2) If you want higher attenuation, you need to mash at a lower temperature, ~148
3) You don't necessarily need higher attenuation. 1.03 will taste good with a beer that big.