Acetalhyde flavor in Russian Imperial Stout...

[mm027]

Hello,
First time starting a thread here but many year brewer. I have had very good success brewing IPA's and Stouts which are my favorite beers. For the first time, I have a batch that went in the keg and has a strong green apple aroma/flavor.

Russian Imperial Stout recipe calculations: 1.118 OG, 1.027 FG
All Grain BIAB process mashed at 152 degrees

I brewed this beer March 26, 2017.

Brew day went really well except I boiled a bit less vigorously than I normally do and ended up with more wort and a slightly lower OG at 1.110 instead of the calculated OG of 1.118
I decided-mostly due to apathy-to pitch the wort on top of a fresh Nottingham yeast cake. The yeast cake came from a 6% abv porter I brewed just prior to this batch. The yeast sat for only a couple days before being used again. I realize I should've calculated my pitch rate and made a proper starter but well...I didn't this time. I figured there would be a large colony ready to chew through this RIS wort.

I aerated well with pure oxygen and diffusion stone for 60 seconds. The fermentation was controlled in my brew chamber at 66 degrees f. 8 hours after pitch it was bubbling away nicely. I let it ferment for 10 days before grabbing an early gravity reading. At this time I noted it was 1.054 I know big beers take a while to ferment so I let it ride for another week. Took a reading and noted it was 1.050 first point I thought I might be stalling out. Whether that was the wrong conclusion or not I decided I would pitch another batch of Nottingham on to the beer. I did this and left it for another couple weeks. Took another reading and it was 1.042 hmmm not really moving fast I thought. So I left it for another week and checked it 1.038 OK I thought its at least working. Left it and checked it a week later and it was at the same gravity. ****. I thought maybe I had mashed too high or maybe the yeast wasn't very viable or maybe my ferment chamber had got too chilled. The later being a possibility as I caught the chamber one day riding down near 50 degrees. A solenoid failed allowing too much chilled air into that side of the ferment chamber. I did correct that though but it may have been too late.

After some frustrated thoughts I decided to just go ahead and cold crash the brew and mark it up as a less than successful batch but it would at least be drinkable. I noted some slight off taste of green apple but thought that was contributed by the yeast in suspension. So I cold crashed for about a week, then kegged it. Now I have a beer that tastes really green apple like. I've read I can restart the fermentation to "finish off and clean up" the beer even after kegging. I suppose that is my question at this point. Can I pull it off gas-just started force carbing yesterday-slowly purge the gas out the keg and get a small starter going, pitch it in the keg at high krausen and see if it cleans up the off flavors and finishes around the proper FG? My theory is the yeast stalled and didn't finish attenuating and as a product of that stall didn't clean up the acetaldehyde. Could the yeast cake already have been too "stressed" from the prior fermentation?


Sorry for the wordy post, I appreciate the input.

 

[mm027]

Does anyone have advice? I appreciate it. Revvy?

 

[mm027]

Pardon my quick typing spelling error in this thread title, I meant "acetaldehyde".

 

[Revvy]

I don't have much to offer on this, sorry. I'm thinking the Nottingham that sat for two days ended up not being the healthiest and contributed to the problem (I've never gone that long with a pitch on yeast cake. Usually I rack the beer away from the cake into a keg on the same day I've planned to brew... Maybe I've left one under a couple of inches of beer over night, but I can't recall.

As to what to do... You don't like the taste of the beer, AND you have a possible fix in re-fermenting the beer. So you won't really losing anything by trying that- warming the beer up and pitching new yeast. It's worth a try.... You could also consider maybe adding something else to the beer to help mask the flavor... you could maybe add coconut along with the yeast to ferment the beer, but also alter the taste profile further... Or something like a dark, minerally sugar... like Jaggery or piloncillo sugar..those dark sugars will ferment, and add another layer of flavor.

Or maybe leave the beer as is, and maybe add booze soaked oak chips in a bag for a week and maybe that flavor will overpower the green apple.

Another option might be to use something like a Waterfilter Randall and run it through a bed of something to flavor it while pouring to your glass.

But honestly, I would try the pitching more yeast idea, if you lose you lose, but if it works you win, and save your beer, and also added another "trick" to your bag. And share the result with us.

 

[stz]

I get strong green apple at the end of all fermentations though it usually reduces after a couple of days conditioning and is eliminated over a couple of weeks of bottle or cask conditioning on viable yeast. Excessive acetaldehyde is produced in the presence of oxygen, though for an RIS I would say that it'd be difficult to get excessive oxygen into a sealed fermenter unless you inadvertently added it after the lag phase because the yeast would rapidly consume it during the growth phase.

On the topic of the yeast cake/abv etc of the prior beer I'll say that the idea of acclimatising yeast or stepping up in abv to 'toughen' up the yeast is from my perspective a myth. All a high abv ferment does is kill more cells and deplete the reserves of those that remain. I will crop yeast once it is 50% of the way through the fermentation and will not crop off anything over 5%. If I needed to fix a big stuck beer I would go to the effort of re pitching by making a large starter and pitching it at high krausen.

I tend to plot a fermentation chart with gravity / time. I try to pitch enough yeast to ensure I'm close to 50% through the fermentation at 24 hours. The next 40%-50% can take the next 48 hours and the final bit another 48 hours which is ideal for dry hopped beers, others I just +3C on the temperature and chill when there. This gives me a good idea of when I've got a problem and when I might need to rouse the yeast, increase the temperature safely or even re pitch. Bear in mind if using dry yeast pitched directly these numbers look stupid because the first 12-36 hours can be hit or miss with dry yeast.

Basically pitch enough yeast to get the job done quickly otherwise you can have problems. 6 weeks in the fermenter is problems. Will it age out? I doubt there is any yeast left in there after 6 weeks and such a long cold crash.

 

[mm027]

Thanks for the replies. I appreciate the advice. I'll sit down and decide my approach for salvaging this beer and post about the results down the line. Thanks again!

 

[LLBeanJ]

I think you're right that it really didn't finish fermenting, which is where the acetaldehyde is coming from.

If I were in your situation, I'd leave the keg in the fridge for now, but remove it from the gas and start decarbing. Since you just started carbing, it's probably not very carbed anyway. In the meantime, brew up another beer and keg it when it's done. A day before you keg the new brew, pull the RIS keg from the fridge, allow it to warm up for a day or so and CO2 transfer it on top of the yeast cake from the new brew to see if it can finish up. Not much to lose at this point and I'm pretty sure it would work.

 

[Buckeye_Brewer1]

I had a similar issue in a wheat beer however I hit my FG target but took beer off the yeast cake to soon for cleanup to occur. After reading a ton and not wanting to mess with adding more yeast I tried a solution mentioned in another post. I let my keg rise to room temperature and added crushed campden tablets into the beer. I did this in 1/2 tablet increments over a 4 day period. I ended up using two tablets total. I read that you can over add the campden tablets which can then create other off flavors. At first I would still smell green apple but the flavor was greatly reduced. After 1-2 weeks I can still get a slight green apple aroma but I have to be looking for it.

If you are trying to get the FG down as well, I would try a yeast based option. If you just want to address the green apple flavor you can go the campden tablet route. If you use the tablets just be patient and use in small increments over several days.