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Stuck fermentation


PeteB

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I have just done a single malt ferment, lautered. Ferment took off at 27c and produced a lot of foam but it stopped at 9 brix. I suspect it got too hot. Any ideas how to re-start?

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@PeteB What was the max temp of fermentation? blue star is right, if it was just the temperature, repitching should do it. However, you may have contamination if you let it sit too long without active yeast and only bacteria to feed on fermentable sugars. may want to check the pH as well.

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I don't know what the maximum temperature was because It started overnight then I was away the next day. I did try dry pitching more yeast in a small sample as soon as I noticed it had "stuck" but could get no activity.

Tried some yeast food as well but still won't start. I might try re-activating dry yeast in fresh wort then pitching that.

The ferment still smells almost as expected although not quite as fruity as usual.

I ran some of it through the still and the yield was very low.

 

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What was:

  • initial gravity (Im assuming you didnt try to make a 15% beer)
  • volume of ferment (we rarely have small, < 400 liters batches crap out due to exothermicity  <-- I dont think this is a real word)
  • current pH (we have had some batches crap out due to plummeting pH)
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2 hours ago, indyspirits said:

What was:

  • initial gravity (Im assuming you didnt try to make a 15% beer)
  • volume of ferment (we rarely have small, < 400 liters batches crap out due to exothermicity  <-- I dont think this is a real word)
  • current pH (we have had some batches crap out due to plummeting pH)

Initial gravity was 1065 now 1014

Fermenter volume 1,500 liters

I don't have a pH meter, paper test at bottom of range maybe 4 or a little above.

Thanks for reply

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Not saying it is either of these, but I can think of two things that haven't been brought up. One being the initial mash temp, if over 150F/65C more alpha and less beta activity, could leave more non-fermentables depending on the modification level of the malt. Also the yeast strain could have poor attenuation, possibly because of the strain or if it was harvested and repitched. Either way if those were the case, nothing can be done now, just something to change for next time.

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New dry Saf Spirit malt yeast was used so that should not be a problem, same as other batches that were good.

Fully modified pilsner malt used, initial mash temperature was 69c, has been 68-69 previous batches which were OK. Not exactly sure of the decimal but might have been high 69 and previous batch rounded up to 69. If 69+ can cause non-fermentables that might be the problem and would explain why re-pitching won't re-start fermentation.

Any more suggestions gladly accepted

Pete

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69c was immediately after grain addition

I haven't done many 100% malted barley mashes but temperatures have been close to this before, but this may have been slightly too high.

I will check with the local malt distillers tomorrow. (after 10 pm here now, not bed time for me yet as I am waiting for still to finish stripping run of a beautiful smelling gewürztraminer brandy in the making)

Thanks.

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Just to add an extra two cents; I would start with checking available sugars (to ensure you achieved a full conversion, and yes I see it was an all malt mash, but this is a habit that can id perhaps other problems), check the pH, raise it to just sub-5 if you can with baking soda or something mildly caustic, oxygenate if you feel saucy (we have used a pvc pipe on an air compressor for a few minutes).  Rehydrate yeast, add go-ferm to it, re pitch.  This pattern works for us if we ever get something stuck.

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I re-checked the mash temperatures and realize I was reading the wrong column.

Strike temperature of water was 72.3 c and after grain added it was 65 c which is same as other mashes. I was thinking that Tom's suggestion of un-fermentable sugars might have been a possibility but that is now unlikely. A series of iodine tests for starch indicated complete conversion during mashing.

Low pH is now a possible suspect. I have to get onto this quickly before "bugs" take over. The only thing I have that I could raise pH with is either Sodium or Potassium Hydroxide.

Is it worth a try??

By the time I get something less harsh the ferment will be lost.

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Yeah if the mash temp is the same that probably isn't it. What is your typical finish gravity? If you aren't that high above, I would just run it through the still versus messing with it.

It might be a stretch, but you could check the malt lot analysis for this lot of malt versus the last, perhaps it has slightly less extract?

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Malt is from the same bulk delivery as previous good ferment a few days before.

Final gravity is usually very close to 1.000, 1.014 is way too high. I have only just started doing 100% malted barley, 7 batches I think, usually do rye.

I have pushed the pH of a sample up to 5 with potassium hydroxide but I still cannot make the yeast start. Tested the yeast in a sugar solution and it took off really well.

If I haven't found a solution by Monday I will distill it and just accept the low yield, but I would love to know what went wrong so I can learn by mistake.

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