Very odd fermentation

[guypettigrew]

Last Saturday (April 9th) I brewed a beer from very straightforward ingredients.

Maris Otter 82.7%, Munich malt 8.3%, pale crystal malt 4.9% and caragold 4.1%. Nothing special there! Hops were Motueka and Wai-Iti to 43 EBUs. In other words, a pale beer which should be nicely hopped.

The yeast was a new White Labs 001 pitched straight into the 23 litres in the FV. Gravity readings were 1.054/5 from the hydrometer and a Brix reading of 13.9/14.0. Different on-line calculators give different conversion factors for Brix to OG, but let's say the OG was around 1.055. Good enough for me!

There was obvious fermentation about 7-8 hours after pitching, with bubbles just slowly emerging from the blow off tube. The FV is a sealed SS Brewtech 7 gallon Chronical. The blow off tube goes into a small bucket of water.

The temperature is held between 19.0C and 20.5C using the SS Brewtech temperature stabilisation system. The 20.5C is an overshoot following warm water being pumped through the heating coil in the FV, and doesn't last long. Fermentation is in a cool garage. For most of the time the temperature is between 19.0C and 20.0C.

The fermentation rate increased over the next few days with bubbles leaving the blow off tube at a rate of >1/second at the height of fermentation.

Over the last couple of days the fermentation rate has slowed, as you would expect. This morning, Sunday April 17th, I was expecting to see the fermentation almost at a standstill and the beer ready for cooling.

But no!! For the first time in this fermentation there were beer bubbles in the blow off tube and bubbles emerging from the blow off tube at a rate of about one every 4-5 seconds, faster than yesterday! Readings are 1.014/15 from the hydrometer, 7.4 Brix. Down to about quarter gravity, where it should be by now.

So, that's the story. The question? Why has the fermentation suddenly got faster again and, oddly, strong enough to push yeast out of the blow off tube? And what should I do? Cool it down now or leave it for another few days? In close on 100 AG brews this is a first for me!

All advice gratefully received.

Thanks.

Guy

[chris2012]

Very interesting, could it have stalled for some reason mid-way through possibly? And now it could be catching up?

If it's still fermenting I don't think it'd cool it down just yet if there's still sugars it can ferment.

[Kev888]

It seems quite a low SG to begin a vigorous stage of fermenting. Normally I'd associate a later surge with either an increase in temperature or a recovery after a shaky start. WRT the latter, I notice you pitched the yeast direct - are you sure the age/date would indicate enough viable cells to avoid under-pitching? (Its often been suggested that the rigours/delays of transit make direct-pitching questionable by the time it reaches our shores).

Another thought is that existing froth/bubbles could simply be pushed up the blow-off tube for other reasons - say a change in relative internal/external temperature and/or pressure.

[orlando]

Maybe nothing to worry about but it can sometimes be a wild yeast infection. The clue will be if it falls below the expected attenuation for that yeast.

[BrannigansLove]

I always build a starter when I use liquid yeast. What was the packaging date on the yeast?

[guypettigrew]

Maybe nothing to worry about but it can sometimes be a wild yeast infection. The clue will be if it falls below the expected attenuation for that yeast.

This was my concern, although it's difficult to see how an infection could get into a sealed container!

I no longer have the original pack for the yeast, but I'm pretty sure the best before date was around the end of September 2016. The packaging date must have only been a month or so before it was pitched.

The fermentation has slowed right down again now, so it's cooling and then I'll run some off for a taste test. Watch this space!

Guy

[Kev888]

Its extremely hard in a hombrew setup for every last post-boil item to be 'completely' sterile, in many cases we really just disinfect sufficiently to stop the infections gaining significance. Many processes have 'some' moments of risk too, exposure to airborne spores whilst filling the fermenter or something of that sort, we can minimise those and make infections very rare events, but its hard to completely remove the possibility so I wouldn't entirely discount it. Fingers crossed that its not, though!

[guypettigrew]

The beer's turned out fine--to my great relief!

Kegged, fined and dry hopped it yesterday. It's cleared and tastes OK today, certainly no infection. A few more days in the keg and it should have gassed up well, and the dry hops should have improved the flavour profile.

There was definitely something odd about the fermentation, though. After chilling it to 6C for 24 hours and dropping it into the keg, the small amount of beer left in the FV had a thick (about 3cm) meringue like topping of yeast. Not something I've seen before.

Guy

[MTW]

There was definitely something odd about the fermentation, though. After chilling it to 6C for 24 hours and dropping it into the keg, the small amount of beer left in the FV had a thick (about 3cm) meringue like topping of yeast. Not something I've seen before.

I find that's completely normal with WLP001 and US-05. The yeast stays on the top after a stable OG is reached and doesn't shift immediately upon chilling. I just rack from under, like you did.

Yeast can be in slightly different phases at the same time, within the FV, I seem to recall. No idea if that happened here, but I've had brews have a moderate 'wave' and then a stronger one, though not quite so late on. I'd also echo Kev's thoughts on any change in the external temperature affecting the bubbling, which is just one reason why I ignore bubbles altogether. The possible under pitch is the other thing.

[guypettigrew]

Thanks MTW. That's reassured me.

I've used 001 before, but not for a long time and not since I fitted the temperature stabilisation system to my SS Brewtech chronical.

Perhaps being able to keep the fermentation temperature stable (approx.+/- 0.75C, mostly +/- 0.5C) has allowed the yeast to behave at its best.

Guy

[Jocky]

Bubbles from an airlock aren't a great indicator of activity. They can easily be caused by changes in temperature or CO2 escaping.

[guypettigrew]

Bubbles from an airlock aren't a great indicator of activity. They can easily be caused by changes in temperature or CO2 escaping.

But if changes in temperature are controlled, as in my system, surely bubbles are a reasonable indicator of fermentation progress?

Guy