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So this is a weird one.

3 weeks ago I made an Xmas beer. I brewed it, pitched the #2 yeast, and put the carboy in my cold dark room (about 70 F) to ferment. The fermentation and krausen began about 18 hours after brewing, and lasted for 6 days or so. I measured the FG and it was spot-on so I continued as planned. All was well.

I really like the recipe so I brewed another batch 2 days ago (on Sunday). I pitched the #2 yeast and again put the same carboy in the same dark room at the same temperature. Again, the fermentation / krausen began about 18 hours after brewing. However, tonight I took a look at the carboy only to find that the krausen has completely sunk to the bottom... 4 days earlier than the identical recipe did the last time.

What happened? It's still fermenting given that I can see the 3-piece airlock bubbling, but what is the deal with the super early krausen drop? I'll give it 7 days, measure the FG, and hope for the best, but can anyone explain the reason that batch 1 went 6 days before the krausen dropped and batch 2 went less than 48 hours?!

  • The bubbles in the airlock could just be CO2 coming out of solution. It may not be a sign of active fermentation. – FishesCycle Nov 26 '14 at 15:46
  • @TobiasPatton CO2 is a byproduct of yeast eating sugar to produce alcohol, so I'd contend that it in fact is a sign. – Haney Nov 26 '14 at 15:59
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    A bubbling airlock certainly indicates that fermentation has occurred, but does not necessarily indicate that fermentation is still occurring. – FishesCycle Nov 26 '14 at 19:13
  • Ahh, I see what you're saying. Might be leftover CO2 from prior fermentation. – Haney Nov 26 '14 at 19:15
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Use a sterile wine thief to get a sample and take a specific gravity of your current product. How does it compare to the final gravity of your previous batch. Since fermentation is still proceeding, we can guess that you haven't reached your target gravity yet. Which means the krausen is heavier that it was last time...

Possible causes...

Did you use different water, or treat your water differently in preparation for the second batch?

Given that it is an Xmas beer, are there any components with limited shelf life? Fruit augments can act differently depending on their freshness. Even if proper sterility is maintained, the chemical make up of ripe fruit is different from that of green fruit.

The white elephant in the room is infection. Are there any off-smells? Aside from the fallen krausen, does your product look any different than last time? Are there more free floating particles than usual? How is the color?

I would suggest that you let the fermentation complete as normal, and see what the result smells like? If you still have a bottle of the previous batch, use it as a basis for comparison (smell, color, taste). Chances are that it will be fine. Small differences happen all the time between batches; after all, yeast is life and life can be unpredictable.

  • Same water (both from a 5 gallon spring water jug from a grocery store). No Xmas ingredients in primary - all secondary so it isn't that. Doesn't smell off to me, seems about the same in appearance, just accelerated. I'll beer thief it in a few here and see what it's doing (and taste it then too). – Haney Nov 26 '14 at 5:46
  • OK current gravity 1.022 expecting 1.014 so clearly not done. Smells good. Yeast still moving about in carboy. Tastes very much like alcohol (but not hot like fusals) and fairly bitter. It is an ale consisting mostly of crystal so it should not be bitter. Guessing that's the yeast I'm tasting and isn't done yet. Thoughts? – Haney Nov 26 '14 at 6:47
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    You could be right about the bitter being the yeast. I only taste young beer when I'm worried about it, so I've never developed a catalog of "Two day old healthy yeast tastes like..." values. Probably a good thing to do during my next batch. From your ruling out fusals, it sounds like you have a well developed palette. I'm out of ideas on this one. But there is a lot of talent on this board, so hopefully someone can enlighten both of us. Best of Luck with this! – Henry Taylor Nov 26 '14 at 15:04
  • Same issue here re: 2 day old beer. Never bothered to try it so I don't know what it should taste like either. I'll taste it again on Saturday which will be a week of primary fermentation. If it tastes good and FG is right then all will be well. I'll update this post if I remember too. – Haney Nov 26 '14 at 15:33
  • Update... Tasted it and measured it again today, down to expected FG of 1.014 on the nose which is good. Still tastes bitter but seems a little less bitter than last night, so I'm going to leave it alone now until Saturday or Sunday and secondary + taste again then. At least fermentation completed, but perhaps too quickly. One thought I had was I noticed the yeast I used was very very fresh, having only been bottled 3 days before I used it. Could be very healthy maybe? Hoping the bitterness goes away in time, regardless. – Haney Nov 26 '14 at 19:45
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Many factors:

  • Was the 2nd yeast of the same lot code?! Yeast is finicky and may simply not react the same way twice if anything is even slightly different in your mix.
  • Was the malt extract exactly the same as the 1st batch? Dry vs. liquid, fresh vs. 2 years old? Anything different in how you prepared additions like Chrystal malt, etc.?
  • Any differences in the boil? EG: Longer or shorter boil time? Longer or shorter time to cool to room temp? Partial boil vs. full volume?
  • Did you change your water in any way? Did it come out of the cold-water tap as before or did you use another source, such as mineral water from a 5 gal container?
  • Did you aerate the wort in exactly the same way the 2nd time?

The fact that fermentation continued means you are probably ok, though any of the above factors might have made it taste slightly different from the first batch. But without industrial quality control of our kitchen or basement environments that's unavoidable and makes homebrew such a joy :)

  • Different malt brands but same malt type (light DME), same yeast from same lab but diff lot code for sure (was only bottled 5 days prior to my using it). Boil was identical in almost every way. Same water. Aerated in basically the same way also. Thanks for your input and info on this! – Haney Dec 6 '14 at 16:12
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    My guess would be the different malt. Much of the krausen is protein and hop resin pushed up by the escaping CO2. Your 2nd malt brand may simply have obtained a different protein/peptide composition according to how it reacted to the vigourousness of your boil and the cold break during the cooling of the wort, vs. your 1st malt brand. – tinypriest Dec 6 '14 at 19:26

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