Fermentation stops a few hours after pitching, and seems dormant for half a day, before resuming activity. This only happens in one out of two fermentation buckets, both pitched the same WLP400 (Wit yeast) from the same starter, and residing in the same temperature-controlled fermentation kloset. The monitoring equipment (a couple of PLAATOs) has been tested, and presumably works as expected (i.e. is registering activity when emulated). What is going on here?

Edit: Filling the wort and pouring the yeast was alternated between the buckets, to ensure roughly similar conditions.

Figure 1: Bucket where fermentation seems dormant. Fermentation activity shown by the green line, temperature control shown by the white.

Bucket where fermentation seems dormant

Figure 2: Bucket with expected fermentation activity. Fermentation activity shown by the green line, temperature control shown by the white.

Bucket with expected fermentation activity

1 Answer 1


If I had to guess the stalled fermentor was the last to be filled and got less of the wort nutrients.

When splitting a single wort into two fermentations. It's important to alternate the filling of the vessels about 10-20% fill before alternating. This blends the wort, so each vessel gets a share of the nutrients that can drop in the cold break.

Edit: Possibly more oxygen than the other fermentor causing a longer growth / lag phase.

  • Thanks for answering. We alternated filling the buckets, and also alternated pouring in the yeast. Of course, there might be differences, but I don’t really believe it is enough to completely stall one of them...
    – FredrikH-R
    Aug 16, 2018 at 22:32
  • @DJHellduck the only other thing I could think of is that the flat liner got way more oxygen and the yeast took longer in a growth phase. The tell would be more trub compared to the other fermentor when done. Aug 16, 2018 at 22:38
  • We aireated thouroughly both the beer and the yeast - the starter might even have been shaken extra for the stalled one, so this could actually be a possible difference. To be honest, I wasn’t aware that you could over-aireate your wort, and all the resources I’ve read emphasize as much aireation as possible... All truths are with modifications I guess, but why would too much oxygen be a problem for fermentation?
    – FredrikH-R
    Aug 16, 2018 at 22:50
  • @DJHellduck it's usually not an issue because it's pretty hard to over oxigenate. But yeasts trigger to stop lag / growth is when oxygen is depleted. Aug 16, 2018 at 23:08
  • Then I guess I might be a master aireator ;) thanks for the clarification though. Care to work it into your answer?
    – FredrikH-R
    Aug 16, 2018 at 23:10

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