Fermentation finished high

[Zee]

I recently brewed a BIPA but the fermentation finished high at 1:024.

Details
34 ltrs brewed, HERMS controlled mash.
Grain Bill - 89% Pale Malt, 6% Midnight Wheat, 5% Carafa Special 2 (sparged).
Yeast used - US.05 x 2 packs hydrated
Mash at 65C with 76C mash out, efficiency was 89% and hit target
Wort oxygenated with aquarium oxygenator for 20 mins
No yeast nutrient but plenty of cold break in FV.
The estimated FG is 1:012 (Beersmith)
Fermented under 8 psi pressure (Fermentasaurus).

I have pulled off 1 litre to a separate jar and added 2g of yeast. There has been no further activity suggesting the ferment is done.

Does anyone have any ideas as to why it has finished so high? aunsure....

 

[Sandimas]

On the face of it, I can't see anything wrong. Although I'm not familiar with the Fermentasaurus and fermenting under pressure.

What temperature did you ferment it at? Was it temp-controlled? My guess would be it got too cold at some point.

 

[Graz]

It can happen for various reasons. What was the OG?

The problem with adding fresh yeast to partially fermented wort is it doesn't always want to get going again as the alcohol already present in inhibits it and also the nutrients it needs may be gone. If you want to try an restart it you need to build up a starter first then introduce some of you wort and see if it will get going from there. Might not work though and might not be worth the hassle.

Assume you've tried the obvious stuff i.e. give it a gentle stir and up the temperature a degree or two?

 

[foxbat]

You're not reading FG with a refractometer are you?

 

[Sadfield]

Did you start fermentation at 8 PSI?

 

[Zee]

Fully temp controlled FV, started at 18.5 C then gradual rise to 21 C.

OG was measured at 1:062

Hydrometer for measurements.

Started at Zero pressure and let it rise to 8 psi during active fermentation.

 

[Sandimas]

Hmm temp sounds fine.

Can you or someone else explain why you ferment under pressure? Just had a quick read up on the Fermentasaurus and from what I can tell it's designed to be pressurised for serving straight from it, not fermenting under pressure. I'm wondering if the pressure has somehow killed your fermentation? I've never heard of fermenting under pressure before and I've been brewing for 8 years.

 

[simon12]

Any chance the yeast was in poor health?

 

[Zephyr259]

The only potentially unusual thing that struck me was 20 mins oxygenation, I'm assuming that this was done with air rather than O2?

 

[Zee]

Oxygenation from direct air using a low level pump.

I haven't had poor yeast health from dry yeast so far, but it is possible. However the fermentation vigour looked healthy enough.

FV under pressure. Generally it is used for lagers to suppress fruity esters and allow you to ferment at ale temps. larger scale FVs (Pro level) will naturally create pressure the bigger the FV is (especially tall narrow conicals). I was just trying it out to see if it completed any quicker. I believe yeast will happily work away up to 30 psi.
I think the Fermentasaurus was originally designed as a unitank to carb during/after conditioning and this also allows for pressurised fermenting as well.

I can't see any process issue so my thoughts turn to an infection or under performing yeast, I have crashed and will keg and carb to see how it turns out.

Maybe I will call it a Hoppy Sweet Porter

I now need to turn a quick brew around to fill the other keg so I can brew and lager my Munich Helles in the FV... Session IPA in creation!