Inadequate attenuation

[Adrian Gresores]

I just brewed and fermented 2 identical 5 gallon batches of a Sam Adams Boston Lager clone. With the first batch the OG, FG, and volumes were exactly as predicted in BeerSmith 3. Specifically, the predicted OG was 1.050 and the FG was 1.011. I used Wyeast Bavarian Lager 2206 yeast (about 350M cells), after creating a starter from a fresh SmackPak. An additional 100M cells from the same starter was stored for future brews. I also used the abbreviated lager method found on Brulosophy.com. In essence, fermentation is started at 52F. I use a fermentation chamber, with an Inkbird controller and a thermowell. When the wort was 50% attenuated (SG 1.030), I dry-hopped and increased the controller temp to 66F. This happened 3 days after pitching. Cold-crashing at 34F started at least 5 days later, and when the SG was stable at 1.011 over 2 days. This happened 6 days after temperature was increased to 66F. The batch was fined with gelatin for 2 days, starting 1 day after temperature was dropped to 34F. The beer was then kegged and force-carbonated.

The second batch was brewed with identical ingredients, quantities, and technique. The only difference is that this yeast starter was created with the 100M cells reserved from the previous starter. The yeast seemed very vigorous when the new starter was created, with CO2 production within 6 hours and very vigorous krausen. I again achieved the OG of 1.050, with 50% attenuation after 3 days of fermentation. As before, dry-hopping was done and the temperature was raised. However, in this situation, SG stabilized at 1.016, not the expected 1.011, as in the previous batch.

Does anyone have any guess as to the cause of the decreased attenuation in the second batch and any suggestions for the future?

Thanks,
Adrian

 

[Nosybear]

Yes. A starter roughly doubles the cell count, some variation given the size of the starter. A couple of things might have happened, the first of which was underpitching. Double 100 x 10^6 cells and you have enough for 200 ml of wort at the standard lager pitch rate of a million cells per milliliter. A second possibility is that when you harvested your cells, you left the least flocculant behind. They're the ones that "finish" the beer when the other cells have dropped out. I'd lean toward that because it looks like the early part of your fermentation went well.

 

[HighVoltageMan!]

I have seen that happen to me on occasion and I can't say with any certainty why it happens. It could be caused in the mash without you knowing it. This accelerated method seems to work pretty good. When I brew a lager I leave it colder longer than 3 days, it's more like 6-7 days and then I bring the temp up slowly to @ 65F. I don't watch the gravity at all until I cold crash it. So it stays at 65 for 5-10 days. Maybe it needs more time, who knows?

How long did the extra cells set in the refrigerator before the second starter was made? How big was the starter? The answer to the question may give a clue as what happened, but I think it would have to be a severe under-pitch for this to be a problem. As long as the wort was aerated with pure oxygen, the yeast can handle an under-pitch. This seems more like the yeast was stressed a bit, but from what it's hard to say.

If you taste the beer and it's doesn't taste sweet, phenolic, fruity or has a lot of sulphur, then the answer is likely in the mash. The mash can add some sweetness, but most sweetness comes from the yeast depending on the strain.

As long as the beer tastes good, then don't worry about, you shouldn't fret too much over a beer that didn't attenuate like you planned. Make note of it and if it happens again try to see if there are any similarities to might give you a clue as to why this happened. I don't get super attenuation with lager yeast, 76% is the upper limit most times. I had a Dunkel finished at 1.018 and it wasn't sweet, so the numbers don't always matter.

Hope that helps.

 

[White Haus Brews]

I also lean towards mash temp as well. Are you sure those were exactly the same? If your second got mashed higher or maintained temp during the mash better that could explain it.

 

[The Brew Mentor]

Many years ago, I was hosting Jamil and Chris White at an event. In all of our conversations it always came back to a statement from them, " It's all about the Yeast!" I think it was Jamil that actually said it, but there was beer involved and the waters may have been a bit muddy.
Take it to heart!
Cheers,
Brian

 

[Nosybear]

Since the repitch is the major variable changed, I tend to agree with Brian ^^^^.

 

[Mark D Pirate]

Was the second batch actually finished? I use 2206 fairly regularly and it sometimes gets a little lazy munching away the last few points.
Do you use aeration / oxygenation ?

 

[Ozarks Mountain Brewery]

generally what can happen with a repitch is it starts to fast because there is too many cells, it doesn't replicate and doesn't build up the correct membrane to last very long, they get full and drop to the bottom kind of what I do at thanksgiving, eat too much too fast and take a nap, it's best to not have too many yeast cells so they develop correctly and ingest the right amino acids build their yeast cells and become strong enough to eat it all slowly rather than get too full too fast

 

[Adrian Gresores]

All your comments are really appreciated. So, I maintained the mash temp as closely as I did with the first batch. In addition, after the fermentation stalled, I krausened with another 100M of 2206. I made a small starter and pitched it when it was at high krausen. However, that only decreased the FG to 1.015. Oh, well. I'll fine with gelatin now and package it. We'll see how it tastes. Thank all of you.

 

[Nosybear]

All your comments are really appreciated. So, I maintained the mash temp as closely as I did with the first batch. In addition, after the fermentation stalled, I krausened with another 100M of 2206. I made a small starter and pitched it when it was at high krausen. However, that only decreased the FG to 1.015. Oh, well. I'll fine with gelatin now and package it. We'll see how it tastes. Thank all of you.

Do you mean 100 billion? 100x10^9? A native English speaker, I read that 100M as 100x10^6, about enough to pitch 100 - 200 ml of wort, a serious underpitch.

 

[Adrian Gresores]

Sorry. I am a native English speaker, too. I wonder how you thought I might not have been. Yes, I did mean 100 Billion cells, 100 x 10^9. My mistake.

 

[Adrian Gresores]

Was the second batch actually finished? I use 2206 fairly regularly and it sometimes gets a little lazy munching away the last few points.
Do you use aeration / oxygenation ?

I oxygenate.

 

[Nosybear]

Sorry. I am a native English speaker, too. I wonder how you thought I might not have been. Yes, I did mean 100 Billion cells, 100 x 10^9. My mistake.

I'm also a German speaker, where 100 M would be 100 Milliarde, or 100x10^9, a billion in English. Our notation is not universal, that's why I asked. Also because it would be a cause of underattenuation woes to use that little yeast in a full-size batch. Just curious: How did you know how many cells were in your krauesen?

 

[Adrian Gresores]

Ahh. Now, that makes sense. For the krausen, I used the 100 billion cells that were overproduced from the last starter, as per
Homebrew Dad's Online Yeast Starter Calculator, and added it to 1 quart distilled water with 113 g DME. I spun it on a stir plate for about 12 hours, noted high krausen then, and pitched it.

By the way, I finally just tasted the beer (before cold-crashing or packaging). It tastes fine.