Effects of grossly over pitching yeast ?

[Nick_D]

I'm still alive, and still suffering the same issues anytime I try to brew with even the most conservative lager fermentation scheme. Namely, underattenuation, and boat loads of acetaldehyde and diacetyl. I've tried different yeasts, shaken starters, stirred starters, pure O2 with flow meter at pitching, sterile air pumped for several hours at pitching. Fermenting warm (~ 10 C), cold. Raising temp for the classic D-rest even. Yeast nutrients, including the fabled Servomyces.

My FFT show good attlenuation (e.g. 1.048 - 1.008 or better). My ferm temp probe is calibrated. My wort ph is good (~ 5.2 into fermenter). No O2 meter yet.... but several hours of air through an air stone ought to get things up and away.

So over pitching. My last batch I tried was 10 liters. I pitched approx 170 ml of super dense slurry. Too much? FFT was 1.009 (mash temps were a bit messy), but the batch got stuck at 1.0125 ish (bottle conditioning/spunding).

I've been so concerned with getting 'enough' yeast, thinking this is the issue (i.e. not enough) that it occurs to me I may have been pushing the wrong direction. As anecdotal evidence of this, I did a Dunkel a long way back, and pitched assuming approx 4 billion cells per ml of dense sediment. This beer turned out well, albeit very sweet due to using too much munich II (100%).

A very subjective question. How much acetaldehyde and diacetyl is in your beers at transfer ? For me, I can't even taste the malt, or hop character -it's that bad.

My plan is to direct pitch one vial to 10 liters of wort (in case my starter method is doing harm), and aerate with sterile air for 5 or so hours. See where that gets me. It will be many magnitudes less yeast than I've been pitching.

Sorry for the long post, as ever. I appreciate all of your past advices, and appreciate your patience.

Nick

[wobdee]

Does this only happen when you spund? Sounds like your stalling out during transfer for some reason. Maybe you need a little more time or higher spunding temp?

I've only spund a few times and found it not worth it for my smaller batches, I ferment to FG in 8-9 days at 8c then slowly drop to lagering temp then transfer to keg and force carb. My transfer sample always seem clean tasting but there is little yeast in suspension. I pitch about 250-300ml slurry for 11 liter batch and my FG is almost always the same as my FFT, sometimes 1 point higher.

[Nick_D]

[wobdee]

[Nick_D]

[Techbrau]

If you have had that many ruined batches over so long I think you are doing something fundamentally wrong with your process that you are unaware of.

Next time just try two packets of rehydrated dry W34/70 to establish a baseline. Depending on the results you get with that you can narrow down the list of possible causes.

[Nick_D]

[Techbrau]

One pack for 10 liters. Strictly speaking dry yeast does not really require aeration as it is grown aerobically in a medium whose glucose content is below the Crabtree threshold, allowing the ergosterol content of the yeast cells to grow to as much as 5% by dry weight (anaerobic growth will only ever result in about 1%). The cells have enough sterols to divide at least 4-5 times without requiring any oxygen, and 4 divisions is approximately what you need to get from a single packet of yeast to reach maximum cell density (about 200 billion cells per liter) for 10 liters of wort. That said it may still be beneficial to aerate a bit.

If you're blowing air through your wort for several hours straight and not having foam overflow your fermenter I have to wonder if you're getting much air in there at all, which could explain the problems you're having.

[Nick_D]

[Owenbräu]