Stout hasn't reached final gravity

[Larse]

I'll try and make this as short as possible. I brewed an oat stout almost two weeks ago - Target OG/FG is 1.045/1.011. Mash temp was 66° which I pretty much nailed for the hour. After sparge and boil (whirfloc and yeast nutrient added) I had ~23l of wort which came out at 1.052. I've been getting these kinds of overshoots ever since I started adding 5% rice hulls to the grist, so just topped up with ~3.8l water to get ~27l.

Pitched the yeast (S-04) rehydrated at 22° and left it do its thing. 30 hours later I had a very vigorous fermentation going.

I lowered the temp to 20° and over the next 24 hours or so, the SG had dropped to 1.018. At that point I disconnected the bubbler and left the spunding valve on at ~8psi.

Then it all slowed down. It dropped to 1.016 over the next 12 hours, but has pretty much stayed like that since then. The krausen had pretty much all dropped to the bottom of the fermenter, so I roused it gently and raised the temp to 22° and it dropped to 1.015. I left it at 22° for a couple of days, but nothing changed so I dropped it back to 20°. Three days ago I added a teaspoon of Alpha Amylase, roused the yeast again and raised the temp to 23°. No good reason for this other than trying everything at this stage.

There may be a calibration issue with my Graviator, I took a sample and put the analogue hydrometer in it and it was reading 1.014, so not significant, but will re-calibrate the Graviator when this is finished.

So the questions for you good folks out there. Should I just take the L and package or should I assume the AA has done its job, but needs fresh yeasties to take over.

I would add that in preparation for whatever the consensus is I started lowering the temp again to 20° (either to start a cold crash or pitch new yeast) and lo and behold, the SG went up to 1.017. That could be the effect of temp, but since I'd already been at that mark with an SG of 1.015-6, I'm wondering is it caused by the AA. Don't have much experience with the stuff, so I'm just guessing.

Anyhow thanks for reading and hopefully coming up with answers.

Edit: Just to add the Graviator data. The spike on 15/10 was when I added the AA. I also cleaned the Graviator which was covered in krausen, so I had it in a jug of steriliser while I was adding the AA.

 

[YeastFace]

Your grain bill may have had an impact on attenuation, can you post it?

 

[YeastFace]

Also what temperature is your hydrometer calibrated to?

 

[Larse]

Your grain bill may have had an impact on attenuation, can you post it?

Thanks, yes. Although I should add that this hasn't been the first time I've under attenuated, last two brews struggled to get within 2-3 points of target. Those were lagers.

3.7Kg Pale Ale
300g Chocolate
200g Roast Barley
200g Dark Crystal
200g Light Crystal
450g Cracked Oats
Also 250g Rice Hulls.

Just edited to answer your supplementary - 20°

 

[YeastFace]

Sorry, one more question. How much yeast did you pitch?

 

[Larse]

Sorry, one more question. How much yeast did you pitch?

One pack of S-04. 11.5g

 

[Sadfield]

11.5g of yeast in 27L of wort is 0.43 g/L. Fermentis recommend 0.5-0.8g/L

For a dark wort that will contain complex sugars you really want to be aiming for the higher end.

 

[Larse]

11.5g of yeast in 27L of wort is 0.43 g/L. Fermentis recommend 0.5-0.8g/L

For a dark wort that will contain complex sugars you really want to be aiming for the higher end.

Thanks

So should I pitch more? And dry, rehydrated or started?

 

[YeastFace]

What @Sadfield said.

An underpitch will affect cell growth which can affect expected yeast performance, including attenuation.

If it tastes and smells fine otherwise, and no obvious off-flavours, just enjoy the slightly fuller beer. It's also not too far off the specs.

I wouldn't repitch at this stage, you might end up doing more harm than good now the beer is essentially "finished".

 

[Sadfield]

Thanks

So should I pitch more? And dry, rehydrated or started?

What @YeastFace said.

How are you packaging? Keg or bottle?

If this a recurring issue, I suggest downloading the Fermentis and Lallemand apps. They both have pitch rate calculators that take yeast strain, gravity, volume and pitch temperature into account.

 

[Brew_DD2]

It's at the lower end of attenuation for the yeast, but sounds like it's finished.

How accurate are your mash temps? Maybe mashed a bit higher than you think?

 

[Larse]

What @YeastFace said.

How are you packaging? Keg or bottle?

If this a recurring issue, I suggest downloading the Fermentis and Lallemand apps. They both have pitch rate calculators that take yeast strain, gravity, volume and pitch temperature into account.

Packaging in kegs. Thanks for the tip, but it's a bit odd since the previous two were from a liquid yeast that was started in advance and produced a great deal of yeast slurry.

But this one was definitely under-pitched, had not expected so much wort nor the overshoot, so really should have doubled up. Just didn't occur to me.

 

[Larse]

It's at the lower end of attenuation for the yeast, but sounds like it's finished.

How accurate are your mash temps? Maybe mashed a bit higher than you think?

Very accurate. I think I posted elsewhere that I make sure the strike water is at the correct temperature to reach mash temp when the grains are added. I don't use heating in a 60 minute mash, just heavily insulate the kettle and check the temperature regularly with a stick thermometer. Temperature never went above 66° except probably for the first minute or so as the grain was added.