Cold Fermentation method keeps failing me (stalling)

[Big Monk]

[Nick_D]

Hmmm. I realise this is a rather subjective question, but what would you say would be the upper limit for final gravity on a dunkel with the OG I started out with? I mean, in order for it to be decently sessionable and in keeping with examples of the style. IBU'S would be about 19 on my current batch, so that won't balance out well if it comes in at 1.016.
I may opt to dump it if the FFT doesn't go much further, and re-brew it with the grist you both have mentioned, using the yeast collected from this (potentially) failed batch.

[wobdee]

If it were me I'd just let it go and see what happens. If it turns out with a high FG i'd still drink it and call it a Czech Dark, but that's me.

[Big Monk]

Definitely take any advice I give as well intentioned, but lacking in practical experience. I haven't brewed lodo yet.

Given what some of the members here have said though, 80-82% AA seems like a nice working range. So:

F.G. = ~1.009-1.010

[Techbrau]

Dunkels are fine with a bit lower attenuation. I would shoot for 76-78%.

[Nick_D]

Thanks for all of the advice guys. Ok, I think I'll let it go, as I'm brewing other beers next (Maerzen, Pils) and that will give my dunkel time to reveal itself. Can always re-brew after the others if it doesn't come up to scratch.

Thanks again. Will document the saga.

[Nick_D]

Ok, so I just racked the dunkel for spunding. FFT never went beyond 1.016, so I racked at 1.019.

Following the traditional warm fermentation schedule Nico references on his blog (great blog by the way..) I pitched at 7.5C, raised to 11C over 3 days, then immediately began cooling by 1C per day (manually setting 0.5C lower every 12 hours). Now at 6C at time of transfer.

In the last 24 hours, it seemed air lock activity had stopped, and the krausen had dropped completely, with just a few clusters of bubbles on the surface (see picture). When transferring the beer, it was very, very clear. Looks like the yeast have flocc'd pretty hard, and that's not what I wanted to see. So I picked up a little of the yeast from the bottom and made sure it got in the spunding keg. How clear should the beer be at transfer to spunding ? Does your beer look like mine in the main fermented before transfer? or does it look more active?


This is deja vu for me, as the same thing happened on the last two beers that went down the drain..... I strongly suspect this one will not get to proper attenuation either.

Pitch details: Pitched 120ml of dense yeast cake (Wyeast 2308) collected from the previous batch (which suffered the same issue). Aerated pure oxygen at 1L per minute for 1.5 mins. Had strong krausen and activity within 24 hrs.

I hold my wort in a CO2 purged keg under low sealing pressure (3 psi) overnight whilst reaching pitching temp, and leave behind any trub material that settles in that time before transfer to fermentation vessel. So my yeast ought to be of high density.

I have recently come across a comment @Bryan R made, that he injects pure O2 at 1/4 L per minute for 5 mins, with stirring to reach proper oxygen levels. This leads me to believe I have been short on oxygenation every time. But will do this for my next batch. Until I can afford a DO meter, I'm shooting in the dark. Could this under oxygenation lead to the attenuation/early floc issues I'm seeing?

Is it worth pitching the yeast collected from my dunkel (after some rinsing) for my next attempt at this (a Maerzen). Or Should I be culturing up a fresh batch ? Not too keen on buying a fresh vial again, if I can avoid it.

I know that's a mega post, again. I really do appreciate all the help you guys are giving me here. I'm determined to crack this nut!

Thanks,

Nick

[Techbrau]

Repitched yeast from a cake is oxygen starved. It needs more oxygen than yeast from a starter. I would bet you're not giving them enough, which would definitely cause your attenuation problems.

[Nick_D]

Thanks for the reply Techbrau!

Hmm, I see. Like I said, I'm flying blind currently without an oxygen meter. But how much extra oxygen do you think would be needed? If 1/4 L per min pure O2 for 5 mins gives around 8 ppm dissolved oxygen (estimate), 20% more? 50% ? Can you give me a ball park figure? I'd rather over do it with the O2 a little, and suffer some oxidation damage to the product, than have this same attenuation problem again. Granted, I've probably been below the minimum 8 ppm DO level in these brews in hindsight, so Just getting THAT much DO will be a step in the right direction.

Thanks again.

[Techbrau]

Without a DO meter you don't have an easy way of knowing how much you're getting in.

What I would recommend instead is this: make a starter for every batch, and aerate it well. You can use a stir plate or just vigorously shake it every time you walk buy. Getting air in is most important early on during the growth phase; you can put it on the stir plate for the first 12 hours or so and then take it off, giving it a good shake every so often.

I would inoculate the starter with a couple tablespoons of thick yeast sediment from the cake, maybe up to a quarter of a cup. Use 10 Plato starter wort, and assume that every liter of the starter will grow 100 billion new cells. I let my starters go at 10 c for about 3 days before cold crashing them. Decant and pitch within 2 or 3 days of crashing.

You'll still want to get a little oxygen into the wort after you pitch the yeast, but since the yeast are already going in much more healthy you are less likely to run into the attenuation problems you've been having.