Spunding, thought I nailed the timing, but...

[McKnuckle]

I've fermented under pressure before, but decided to give traditional spunding a try on an Altbier. Yeast is K-97, OG was 1.050. I anticipated that I'd have between 75-80% attenuation, or 1.012-1.010 FG.

Once the blow-off bubbles began in earnest (~20 hrs), I took a small sample from which to gauge fermentation progress with a refractometer (using correction).

Progress:
20 hrs, OG = 1.040
31 hrs, OG = 1.031
38 hrs, OG = 1.016

At that point, I was between 4-6 points of my predicted FG, so I transferred to the keg and attached a spunding valve.

Within about 9 hours, the gauge was reading 5 psi. Then I went to bed. Next morning, the gauge is only at 7 psi. It's been about 17 hours since I attached it. There's no leak, and it's sitting at 66ºF.

Meanwhile, my pulled beer sample is now reading 1.010, which is the lower end of the predicted FG range. I should have had 6 gravity points to work with.

Did my kegged beer peter out before reaching the same FG as the sample? Or did it actually progress faster than the sample and I missed my opportunity? Did I not transfer enough yeast to complete the job (K-97 leaves a pile of krausen on top)? Does it take much longer to build pressure? I'm a bit stumped.

 

[Dland]

Even though you don't think there are any leaks, I can offer guess or two;

Is it possible keg top seal(s) leaked? they sometimes don't seat fully on their own. To be sure they seat, a hit of tank CO2 just after kegging works ( I like to hear them ''creak into place'', makes me sure they have sealed).

Is is possible spunding valve leaked? Keg post seals are not always that great, and the spunding valves can leak, especially if they got some beer residue in them from a prior batch. Even though it pressureized up to 7 PSI, it does not mean it could not leak above that.

Edit: By keg post seal I meant the seal on fitting that attaches to keg post.

I actually do not attach my spunding valves any more if only around .004-6 left to go. I just check pressure with gauge once a day. I'll attach valve if it has headed past 30 PSI at 50-60F so it does not over carbonate, and this hardly ever happens when using a normal yeast.

I have never seen my samples work faster than main batch if at same temp, but who knows.

My guess is there is plenty of yeast still in the beer after kegging, unless K-97 is a freak "super flocker" or something.

 

[RPh_Guy]

The FFT you should keep warm so it ferments quickly and gives you the FG. Very slow stirring may also help.

The FFT is not to monitor fermentation progress of the batch. You do still need to monitor the batch s.g. maybe 1-2 times a day to predict and confirm when it needs to be transferred.

It sounds like in this case the main batch finished before your FFT.

 

[Dustin_J]

Keep in mind too that when you transfer to spund, you're getting rid of a lot of yeast. It's the "stragglers" that haven't flocculated out yet that are finishing the job for you, and if they're not very healthy and ready to keep going, it can take a few days.

One step in diagnosing if there's a problem and, if so, what it is/might be, would be to pull a sample from the keg and take a gravity reading. If it's down near the FFT, you probably have a leak of some sort. If not, things are just going slowly.

If the sample hasn't dropped that much, it means your straggler yeast cells are working slowly. Rousing and bumping the temp up a few degrees might help a bit, but you'll probably just need some time.

 

[McKnuckle]

Thanks guys for the helpful suggestions. I really don't think I have a leak, as the keg was just drained of a prior batch, rinsed, sanitized, and put back in action. But I will do more to confirm that next time.

K-97 is definitely no super-floccer! It's known to be dusty and take its time. It's probably just a timing misstep between the sample and the main batch. Although I really would have assumed that the sample would progress faster, not the other way around, so go figure.

I've had success before taking a hydrometer sample once fermentation is underway, and leaving it, covered, next to the fermenter. That way both are at the same temp, and the hydro jar contains a microcosm of what's in the fermenter. I haven't strictly done an A/B to confirm that they progress at the same rate, but it seems like they do. But... maybe not.

For the next effort, I'll sample along the way directly from the fermenter to remove that variable.

Also, yeah, I'll take a sample from the keg soon to confirm that it's down to the same FG. Maybe it will continue to progress very slowly due to the depleted yeast population.