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Each of my last four batches has stalled well above FG. The first two restarted after bottling and caused bottle bombs.

The last batch was a kolsch with OG 1.047. Wyeast 2565. Stalled at 1.024 for three weeks, even after I raised the temperature to 70F. I pitched a new pack of the same yeast, and 10 days later it was down to 1.004.

This batch is an IPA. 8lb 2-row, 1/2lb Munich, 1/2lb C40. Mashed at 154. OG was 1.072. It was only 2.75 gallons, so I pitched a single pack of Wyeast 1056 at 66F. It blew off about 1 cup in the first two days, then the yeast settled out. After a week it was at 1.020, so I raised the temp to 70F. Four days later it's still at 1.020.

I never had this problem in my first 10 batches. Why might it be happening now?

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As far as the kolch, that's a pseudo-lager and really needs twice the cell count as an ale.

The ale was an also an underpitch with an OG of 1.072 should have had two packs.

Edit: Just noticed it was 2.75g, (sorry i've had a few) underpitch shouldn't be the issue on this one. At 154 mash and the crystal could put TG at 1.020. I suspect maybe mash temp calibration was off with closer to 159 Because of the blow off you noted, making a less fermentable wort.

To avoid this in the furture. I'd recommend oxygenation with pure o2, and do a starter to grow to proper pitch cell counts.

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  • Hmm, thanks. The yeast was only 15 days old according to the date stamp. I aerated for 20 minutes with an aquarium pump, which is the most I've done. I don't think my mash temp was that far off, but maybe it was. I guess next time I'll try a starter.
    – Josh Yeager
    Apr 19, 2018 at 3:05
  • @JoshYeager I would raise the temp a few more degrees up to 75ish and swirl the fermenter to get the yeast back in suspension. Or you can pitch a lager strain at ale temps which will consume maltotriose a sugar ale strains can't use, may help get the FG lower.
    – Evil Zymurgist
    Apr 19, 2018 at 14:09
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    I raised the temp to 75F and swirled heavily. I've had active bubbles in the airlock and visible yeast in suspension for 3 days. Any idea why the yeast gave up before the first time?
    – Josh Yeager
    Apr 22, 2018 at 17:47
  • @JoshYeager the triggers for flocculation arn't completely understood yet. And vary widely among strains. Yeast start to flocculate late growth stage, then reach a point where they stop feeding and don't have those bonds broke mechanically from co2 bouancy. Once they floc they get less cell wall contact to wort and further reduces feeding. Some think that reduction in nutrients, ph change, and ethanol levels play a roll. Sorry but there really isn't an esablished reason for it yet. But microbiologist are working on the puzzle. wyeastlab.com/clarificationflocculation
    – Evil Zymurgist
    Apr 22, 2018 at 18:10
  • @JoshYeager basically by raising the temp and swirling, you broke much of the flocculation bonds and raised the yeast metabolism to be able to feed again in a "hostile" environment.
    – Evil Zymurgist
    Apr 22, 2018 at 18:17

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