Help with stuck fermentation

[wootman]

Two weeks ago I brewed Biermunchers black pearl porter and used mangrove jack m03 yeast (recommended by LHBS guy, last time I use this yeast). Starting OG was 1.068 and after two weeks at about 68f I'm only down to 1.036. I've tried rousing the yeast but nothing happened. Should I rep itch with another yeast???


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[morticaixavier]

any chance you're checking gravity with a refractometer instead of a hydrometer?

If not, I've head the mangrove Jack yeast can be a bit finicky. you can try raising the temp up to ~72 and swirling (gently) to get the yeast back into suspension.

what's the recipe? all grain or extract? that' would help.

Unfortunatly it's really hard to get a stuck ferment going again but after two weeks it should still be possible.

 

[wootman]

Definitely checking gravity with a hydrometer. I followed the all grain recipe exactly except I scaled back the maltodextrine and lactose a bit. The only thing I can figure is the yeast pooped out on me early.


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[mattmmille]

any chance you're checking gravity with a refractometer instead of a hydrometer?

I'm in a similar boat, with a strawberry blonde...I used a hydrometer initially, but just got a refractometer for my birthday and used it for my current readings. Is that a problem?

 

[kombat]

I used a hydrometer initially, but just got a refractometer for my birthday and used it for my current readings. Is that a problem?

Yes. Refractometers are inaccurate in the presence of alcohol (they read waaay too high). You must do a conversion. There's a tool built into BeerSmith that will convert for you. I use it for my 1-gallon batches when the amount of beer I'd have to pull to fill my hydrometer test tube comprises a nontrivial volume of the total batch.

 

[mattmmille]

Yes. Refractometers are inaccurate in the presence of alcohol (they read waaay too high). You must do a conversion. There's a tool built into BeerSmith that will convert for you. I use it for my 1-gallon batches when the amount of beer I'd have to pull to fill my hydrometer test tube comprises a nontrivial volume of the total batch.

Awesome! I did not know that...thank you!

 

[morticaixavier]

Quick check on Sean Terril's refractometer calculator and it looks like you are ~1.017. which is respectable. 75% attenuation is about what I would expect in a porter recipe.

 

[wootman]

Quick check on Sean Terril's refractometer calculator and it looks like you are ~1.017. which is respectable. 75% attenuation is about what I would expect in a porter recipe.

I'm not using a refractometer...


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[duboman]

I'm not using a refractometer...


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Confused... Your above post stated the most recent reading was a refractometer. Which is it?

Btw, what was your mash temp and is your thermometer properly calibrated? You may have mashed at a higher temp creating a less fermentable wort. Also, is your hydrometer/refractometer calibrated and are your readings temp corrected?


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[morticaixavier]

I'm not using a refractometer...


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Oops, my bad. I got two posters confused. so, hmm.

the reasons I can think of for yeast pooping out as you say is because it got way too cold or the wort was way too high gravity or way too unfermentable. 1.068 is not too high gravity and you say you left out the maltodextrine and lactose both of which are unfermentable.

unless your thermo is way off and you actually mashed much higher than you intended I'm not sure. Looks like the recipe calls for a sach rest at 158 so if your thermo was ~5-10 degrees low at mash temps you may just be done. nothing (good) you can do about it now except brew a really light bodied beer to blend. maybe the same recipe but mash at ~148 for 90 minutes and let that ferment out all the way to 1.003 and blend. 1:1 would get you around 1.019.

I have also heard of stalls because a high initial ferm temp causes the yeast to run wild and they will sometimes drop out early leaving significant sugars behind.

another option is that it's just not done yet. sometimes bigger beers take longer.

 

[wootman]

What about pitching a clean fermenting yeast to clean up a bit? Something like WL001? Or I could pitch the mangrove jack M03 again?


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[morticaixavier]

What about pitching a clean fermenting yeast to clean up a bit? Something like WL001? Or I could pitch the mangrove jack M03 again?


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If the problem is that the yeast dropped before they were done that might work. The problem there is that the beer has now become a fairly inhospitable environment for yeast. lot's of alcohol and low pH so it's hard for a new population to get started. you can make a big starter, wait till it's at high krausen and pitch that. it might work.

If the problem is a less fermentable wort than you meant then no clean yeast is going to help. a crazy attenuative yeast (think brett) might over time but not quickly and not cleanly.

If you are pretty sure your mash temp wasn't way too high try the active starter and see what happens!