Stout hasn't reached final gravity

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.

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

Also what temperature is your hydrometer calibrated to?

YeastFace said:

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

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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°

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

YeastFace said:

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

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One pack of S-04. 11.5g

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.

Sadfield said:

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.

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Thanks

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

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".

Larse said:

Thanks

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

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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.

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?

Sadfield said:

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.

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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.

Brew_DD2 said:

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?

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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.

I can't see that grain bill getting within a bulls roar of 1,052 in 23 litres.

foxy said:

I can't see that grain bill getting within a bulls roar of 1,052 in 23 litres.

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I understand your disbelief because it mirrors mine. But I checked it three times. First with the analogue hydrometer with temperature correction (didn't believe that one), then again with the same instrument when it had cooled to 22° and again with the Graviator.

Did the calculations for overshoot and it said to add 4l. I just added a bit under that and stirred vigorously and all instruments said 1.045.

The only thing I can attribute it to is the addition of rice hulls. Since I've started using them, I have consistently overshot. This particular mash was the cleanest I've ever seen. Very little trub at the bottom of the kettle which meant I was able to drain more wort than usual. I'd normally leave a couple of litres in the kettle, but this time probably less than a pint.

Larse said:

I understand your disbelief because it mirrors mine. But I checked it three times. First with the analogue hydrometer with temperature correction (didn't believe that one), then again with the same instrument when it had cooled to 22° and again with the Graviator.

Did the calculations for overshoot and it said to add 4l. I just added a bit under that and stirred vigorously and all instruments said 1.045.

The only thing I can attribute it to is the addition of rice hulls. Since I've started using them, I have consistently overshot. This particular mash was the cleanest I've ever seen. Very little trub at the bottom of the kettle which meant I was able to drain more wort than usual. I'd normally leave a couple of litres in the kettle, but this time probably less than a pint.

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Rice hulls will add nothing apart from residue of pesticides and weed killer if you didn't wash it. The chocolate and roast malts will add a poofteenth of fermentables and the crystal malts a bit more than a poofteenth.
Whichever calculator you are using to get to 1,045 I would be more inclined to believe that. Where did you take the wort sample from?

This is a shop bought all grain kit isn’t it? So there is no way to know how generous the weights are @foxy

Personally it had already fermented out fine before the AA went in, it was never going to 1.011. The enzyme throws a curve ball - if it’s intended for bottling no one can tell if that is safe.

I do recommend running a forced fermentation test taken from about 120ml sample the day after pitching.

foxy said:

Rice hulls will add nothing apart from residue of pesticides and weed killer if you didn't wash it. The chocolate and roast malts will add a poofteenth of fermentables and the crystal malts a bit more than a poofteenth.
Whichever calculator you are using to get to 1,045 I would be more inclined to believe that. Where did you take the wort sample from?

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The purpose of the rice hulls is to allow for better circulation in the mash, not to add sugars. They are entirely neutral and purchased from GEB for that purpose, so already prepared for brewing.

The grains came in a kit from GEB, the target OG was theirs. First gravity reading was taken in the kettle at 60° with temperature adjustment taken from the BF calculator. Second was when cooled, again in the kettle, third taken in the FV with my Graviator.

Edit: @Caramel Ox - It's going to be kegged. Next question, to prime or not to prime? My thinking is to prime and this may bring down the FG if there is still active yeast there and fermentable sugars from after AA addition.

Yes keg prime and enjoy then! And stop worrying about the numbers.

Then you can decide if you like it - it’s a bit of a kitchen sink recipe, more like porter than stout to my eyes.

Larse said:

The purpose of the rice hulls is to allow for better circulation in the mash, not to add sugars. They are entirely neutral and purchased from GEB for that purpose, so already prepared for brewing.

The grains came in a kit from GEB, the target OG was theirs. First gravity reading was taken in the kettle at 60° with temperature adjustment taken from the BF calculator. Second was when cooled, again in the kettle, third taken in the FV with my Graviator.

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If you are taking a sample from the kettle do so straight after it has finished boiling while the sugars are in suspension. As wort cools the sugars sink which will give a higher than expected gravity. I wait until I have transferred into the fermenter leaving all the trub behind to take a reading.

Caramel Ox said:

This is a shop bought all grain kit isn’t it? So there is no way to know how generous the weights are @foxy

Personally it had already fermented out fine before the AA went in, it was never going to 1.011. The enzyme throws a curve ball - if it’s intended for bottling no one can tell if that is safe.

I do recommend running a forced fermentation test taken from about 120ml sample the day after pitching.

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I would never use AA, leave that for distillers, it is made up of bacteria which will just keep chomping through all the sugars available.