Extra dry yeast, vs wet, for a stuck fermentation, right?

[MTW]

...cell for cell, because it has a lower oxygen requirement and is entering a low-oxygen, part fermented beer that you don't want to re-aerate? Makes sense to me, though I can't say I've ever read it anywhere!

I'm faced with a beer that dropped from 1.060 to 1.030 in a couple of days with a harvest of London Ale III, and has then slowed enormously (though not quite stuck at the moment) to just a couple of points per day for the next two days. Which all got me thinking through recovery options if matters got worse.

[Eric]

That's quite low attenuation, suggestive of either a very high mash temperature or an acute lack of enzymes in the mash or alternatively, a problem with your yeast.

Yeast does not choose to lower it's oxygen requirement, it does so to survive when none is present after it has consummed all that was. Yeast will typically reduce oxygen level to 1 part per billion from whatever the starting level was, provided both sufficient yeast and neutrient are present.

Dried yeast is supplied with sufficient oxygen for its needs, but live yeast has to be provided with enough oxygen to carry out all the functions a brewer requires of it. Might it be there was insufficient oxygen in the wort for those yeast and their growth phase was reduced, so the remaining yeast were unable to finish the job?

[MTW]

To be honest, Eric, it could be any or all of the factors you mention at the top that has caused the premature slowing down. I thought I'd raise the question about dry yeast being a better pick than (even a healthy starter) of wet yeast for re-pitching, specifically, on this occasion, as I look at the options I have. Doesn't it seem a better idea to repitch with a type of yeast (ie dry) that requires little or no oxygen from the partly fermented beer? I've never seen that discussed before, and just wondered.

Regarding the brew, it was indeed a 69C mash, plus mashout, though it took 25 minutes to get from 63 to 69C while I wrestled the Klarstein to where I wanted it (3rd brew on that - still adjusting; last time I struck too high, hence the lower start this time.) I was measuring the mash temp directly with a Thermapen btw, not relying on the unit's reading.

Stout: 8% malted oats; 4% rolled oats that had a cereal mash first; 15% various roast; a touch of crystal; the rest Maris Otter and a bit of Munich. 90 minute mash, though I didn't do an iodine test (never have). Yeast wise, it was "IPA's method" of harvesting a 500ml bottle of yeasty fermenting wort 24hrs into the previous brew, and letting that ferment out, before starting a litre with DME the day before and pitching active. The harvest was around a month old, but went off really well, even forming a solid kraeusen. I would have preferred to have prepared the starter within 12 or 18 hours of pitching to the main batch, though the family schedule meant doing it about 30 hours before, so it was probably going to sleep a bit I guess, by then. I let it splash from height into the FV and whipped with the spoon for a good few minutes. It also got 0.2g of servomyces. Into the fridge at 19C and it was off really well the next morning, though perhaps slightly less vigorously than the previous, very similar brew, from which the yeast was harvested, judging purely by the bubble rate in the blow off... which I probably shouldn't. That went down to 1.021 in 4 days.

As I mentioned, it's not fully stuck (yet!), but the brakes certainly went on sharply!

[Eric]

A fairly complex recipe, I'm unsure what enzymes malted oats have, but I would guess not enough to have any spare or maybe not even enough for itself.

A starch test probably wouldn't have helped, the wort too dark to see and it would only show that the alpha amylase had done its job and not tell you if the sugars you had were fermentable. 8% plus 4% plus 15% and a touch crystal leaves maybe 70% pale malt to supply the essential enzymes, so there wouldn't be a great deal spare by the end of the mash. Even so, that wouldn't account for all the shortfall you have found.

IPA's method is now well proven and although I don't use it, I can't critisize it and in any case it can't be responsible for any shortage of oxygen or amount at the start of that fermentation. I've not used London III yeast, so can't comment particularly. However I am sceptical that many yeasts of that and similar origins are exactly what is claimed for them.

I would suggest you keep your eye on it and possibly gently rouse the yeast of the bottom or push it back in from wherever it is and raise the temperature a degree to see if it responds. (I've just been out to knock mine back in from Sunday's brew, last night a lot escaped from a 23 litre brew in a 50 litre FV.) Otherwise perhaps a dried yeast like Nottingham to finish it off if it is stuck. You might wish to take off some of that yeast first if you intend using it again and don't want it contaminated with another.

Hop and Grape are selling Brewlab slants if you fancy trying one of theirs.

[Kingfisher4]

Please excuse my incompetence, but I cannot find IPAs method via the search engine, IPA appears so frequently it is deleted!
A link to his method would be great if possible.

[Meatymc]

Please excuse my incompetence, but I cannot find IPAs method via the search engine, IPA appears so frequently it is deleted!
A link to his method would be great if possible.

viewtopic.php?f=2&t=79784&p=826218&hili ... od#p826218

Most of it is contained here although not his original post I used

[Kingfisher4]

Please excuse my incompetence, but I cannot find IPAs method via the search engine, IPA appears so frequently it is deleted!
A link to his method would be great if possible.

viewtopic.php?f=2&t=79784&p=826218&hili ... od#p826218

Most of it is contained here although not his original post I used

Thank you, I will carefully file that away for action soon, particularly as I plan to progress to wet yeast at some point in the near future.