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Strange Fermentation: 12 gallon split into two 6.5G carboys...one incomplete

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OneHotKarl

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Ok, so this is really strange. I split my 12 gallon all-grain batch into two 6.5 gallon carboys and after 3 weeks fermenting, one is at 1.008 and the other is at 1.018....what gives?

So now the details:
  • Its an all-grain double american IPA which was calculated to come out at 7.4%ABV
  • I used a 1800ml starter (as usual) made two days before.
  • The carboy which did not fully ferment had between 0.5 to 1.0 gallons extra versus the carboy that went down to 1.008
  • The taste is very similar, but the one at 1.018 with significantly more sugar taste (as expected)
  • When cooling down from brew kettle (through counter-flow-chiller) the wort hose was alternated between each carboy multiple times to get an 'equal' wort...ultimately ending, and leaving, the 1.018 carboy with more wort
  • I don't taste any infection in either one
So, any guesses?...suggestions?
 

llazy_llama

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I'd look at your yeast, and their viability. If you used 2 vials/packs of yeast, made a starter, and then split it equally, then I'm stumped. If you used 2 vials/packs, and pitched them directly into your carboys, I'd guess that one of your packs had fewer viable yeast cells than the other.

Barring that, one batch could have been aerated less than the other. One could have been at a warmer temperature than the other. Maybe the yeast in one just got lazy and decided to take a little break.
 

Revvy

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Something to remember is that with yeasties, you are dealing with living creatures...every fermentation is different...you can split a batch in half put them in 2 identical carboys, and pitch equal amounts of yeast from the same starter...and have them act completely differently...for some reason on a subatomic level...think about it...yeasties are small...1 degree difference in temp to us, could be a 50 degree difference to them...one fermenter can be a couple degrees warmer because it's closer to a vent all the way across the room and the yeasties take off...

Someone, Grinder I think posted a pic once of 2 carboys touching each other, and one one of the carboys the krausen had formed only on the side that touched the other carboy...probably reacting to the heat of the first fermentation....

I've found that you should never assume anything where the yeasties are concerned except that they are in charge...not us...and they've been doing this beer making stuff for 5, 000 years...so basicially we just need to trust them, and not bug them...and give them plenty of time, and they will make us very very happy.
 

Braid

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Pop a smidge of yeast energizer in there and see if it picks back up.

Did you say the slower fermenter was the one with higher volume of wort? If so, then the yeast just has more work to do and that me be the only reason.
 

TheTower

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Looking at your process, you had one starter, which I assume you split relatively evenly between the two worts. One of the worts had more wort in it, meaning more fermentables, meaning longer time to finish fermentation. Take it to an extreme: If you put one vial liquid yeast in one gallon of wort, and one vial in 10 gallons wort, which would finish faster?
 
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