Underpitched?

[Kinsman]

I brewed a 1050 ale using US-05.
Two weeks later I bottled, and brewed the same, putting the wort on the yeast cake (aerated the hell out of it as I did so).

That ferment took off in just a couple hours and went nuts, blasting up thru the airlock etc. I let it clear, racked and bottled. Left about an inch of wort on it. I swirled then split that slurry between two sanitized pint mason jars and stuck those in the fridge.

Pulled one jar out and within an hour it was showing activity. Couple hours later pitched that to another 1050. It didn't do anything for a day and a half, and when it did show activity, it was pretty weak. Half an inch 'krausen'. It's still going but looking like it's slowing down, and was never really 'normal'.

I thought that as active as that bunch of cells was, it would have been a vigorous ferment.

About a cup of yeasty-looking, smelling, tasting slurry to 2 1/2 gallon of wort (5 lbs Maris Otter, 1/2 lb Munich).

Underpitched? 60 minute mash didn't convert? Something else?

 

[milleniarist]

Most likely your slow fermentation is a result of overpitching. When you raked your second batch on top of the entire yeast cake that was a huge overpitch. Yeast cells need to reproduce during the growth phase to adapt to the amount of food in the wort ideally 3 to 4 fold. If you use the entire yeast cake those cells won't reproduce and start metabolizing sugars immediately (that was your second vigorous fermentation).

The multiplication during the growth phase is vital because it creates new young cells every re-pitch. Otherwise you'll end the fermentation with the same old and tired original population that will eventually die, even worst if you store the slurry for some days in between batches.

I hope this helps for your next brews. I would start fresh with a new packet of US-05 or create a starter from a small portion of your next (washed) yeast cake if you trust your sanitation technique enough.

 

[KeizerBrewr]

From what you said, that sounds like an overpitch. Yeast need to propagate as part of their fermentation cycle. Usually only 8oz of slurry is more than sufficient to inoculate a fresh fermenter of wort. Also, if reusing yeast, go lighter to darker, less IBU to more IBU, low gravity to high gravity. Helps keep the stress levels lower and allow a cleaner flavor for the beer you pitched on top of that cake due to the remaining beer it's suspended in.

 

[Kinsman]

Thanks guys.

My first re-pitch was on the full yeast cake. That ferment went apeshit. I then collected from that and split it. I guess about a cup of slurry went into a 2.5 gallon batch (the 'slow' ferment).

That batch did ferment to 1010, although the expected volcano never happened.

I'm confident that my sanitation is good.

I've still got the other half of that yeast (from the really active ferment). I think I'll try that in the next batch in a day or so. This time I'll shoot for about a half cup of delicious yeasty slurry.

 

[DuncB]

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