Shaking the carboy again

[z-bob]

My Belgian dubbel has been going for a week; 3 gallons in a 4 gal plastic carboy. The krausen almost reached the neck on the third day, but then it dropped an inch or two and the airlock activity slowed way down -- almost stopped.

Last night there was still about 2 inches of thick foam, a lot of nasty floaty things suspended in the beer, and very little sediment on the bottom. I swirled and sloshed the carboy vigorously (airlock still on) to knock down the krausen and the release most of the dissolved CO2. This morning there was a half inch of much looser krausen, several inches of sediment, and the lock is bubbling 2 or 3 times per second again instead of maybe once per minute.

What happened? Was all the yeast was trapped above the waterline in that thick foam? Or were all the suspended trub, hops, and dead yeast somehow inhibiting fermentation? (and they sank after I released all the CO2)

 

[sfrice80]

Really doubt all the yeast was up top. Maybe you had a stuck fermentation and didnt know it. Maybe the shaking woke them up again. After a week though most of that primary fermentation should be done. Whats the temp where it's fermenting? If it dropped down to cool temps it could have slowed fermentation.

 

[z-bob]

The temperature is in the mid-to-high 60's. (it's in the heated part of my basement) Probably about 67°.

The yeast is Wyeast 1762 and I didn't make a starter, so I underpitched it a little. This is my first beer in many years, and the first time I've ever used liquid yeast.

 

[sfrice80]

Might remain a mystery to what exactly happened. I personally think primary fermentation was not quite complete and shaking it either stirred up some unfermented sugars or the yeast got a boost. The dissolved CO2 could have been slowly leaking out. Things I really doubt it was is yeast stuck in the Krausen or the fact you used liquid yeast. Take a gravity reading soon and if it looks good then you're in the clear.

 

[desabat]

Maybe your first aeration wasn't sufficient and shaking it a second time gave it the boost it needed to continue fermentation

 

[fuzzy2133]

I have had a mead start and stop fermenting only to find some honey settled out to the bottom (somehow ). Stirred it back up again and it actively fermented for another week.
One brew never krusened, just churned like normal and made a thin layer of bubbles.

Yest do funny things and the hydro will tell you if they are doing/did their thing.

 

[rlmiller10]

Was it on a concrete floor in the basement? Sitting on a cold floor will drop the temp a couple degrees over the room temp. It can also lead to temp stratification. You might have had a layer of cold wort near the bottom that didn't ferment clear out. Shaking it may have mixed that all up and you are now fermenting those sugars.

 

[z-bob]

Was it on a concrete floor in the basement? Sitting on a cold floor will drop the temp a couple degrees over the room temp. It can also lead to temp stratification. You might have had a layer of cold wort near the bottom that didn't ferment clear out. Shaking it may have mixed that all up and you are now fermenting those sugars.

That's the best explanation I've heard. It is sitting on a concrete floor, although the floor is covered with worn-out indoor/outdoor carpet. I may move it to a table when I get home, or put a sheet of styrofoam under it.

The oxygenation thing "desabat" mentioned makes sense, except the air lock has been on the whole time so there was no O2 in the headspace, just CO2.

I should probably just leave it alone for a month and let it do it's thing.