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I'm a total beginner and really appreciative of any advice here. I'm making a 1 gallon batch of IPA from a kit. I brewed 16 days ago, and in the first 48 hours of the wort being in the fermenter it was bubbling away like crazy. It then settled down and I could see the liquid become less opaque and darker, as the yeast cake formed at the bottom. Today I went to look again as I had planned to bottle this evening, and it's more opaque again, and looks more active. What could be the cause for this. The last few days have been slightly warmer here (it's gone from ~20°C to 25°C), could it be the temperature variation?

In addition to this, I have been measuring the gravity with a refractometer every 3/4 days just to see how it was changing. After the first 3 days it had dropped to 1.034. Since then (almost two weeks now) it has remained at that value, so I thought fermentation must have been over? I have tested my refractometer on water and it seems to be calibrated well. Either way, poor calibration wouldn't account for the value not changing at all.

So, in summary, why does my wort suddenly seem more active again after 16 days, and why hasn't my gravity measurement changed for two weeks?

Thanks in advance for any help!

  • Did you add dry hops? Hops contain enzymes that will restart a fermentation that has otherwise finished. – dmtaylor Jun 1 at 11:58
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I can only guess, but very low ambient temperatures will cause the yeast to slow, which could look like a stall.

I experienced this with a recent batch. It had been cooling here, with an ambient daytime temperature of just below 20C. That's perfect for fermenting ales, so I just leave them outside (under cover). However, the day after I pitched my yeast, and for the next few days we had a big chill. I brought the beer inside the house. I really did observe quite a significant second kräusen form when the brew finally warmed up.

If you really think you have a stall like this, the standard practice is to warm the beer back up to 17-20C. If there's been no obvious cooling, gently rouse the yeast from the bottom of the fermenter by swirling it.

Sometimes if you have bad yeast, or bad procedures, your yeast can fail. In this case you can add more yeast, but really it should never get to this. Given you got a restarting of fermentation, I don't think this is the case. Taking an extra week (or even 2) wont hurt your beer at all. Make another batch while you wait ;)

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Consistent SG readings but more activity, maybe it's physics. The difference in air temperature can take a while to translate into liquid temperature. An increase of a few degrees C might not be apparent in the liquid right away, but as the temperature increases, any dissolved CO2 will want to move out of solution, resulting in an increase in pressure = more bubbles. Of course, this will be exacerbated if you move the fermenter around.

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