Fermentation Stall/stuck?

[TheGad]

Hello,

This is my first experience with a stuck or stalled fermentation. I’ve read tons recommended solutions, many many scenarios, and I’ve tried several attempts to get it going again.
First off - forgot to clock my starting SG.
The mash has been fermenting for 32 hours. Right out of the gate, it was doing great!
Current SG 1.090
I’m using a high tolerance rum yeast.
I thought my SG might have been high so I made another yeast bomb and pitched it with a half gal water. My pH is right at 5.0. I’ve tried warming the mash even though recommended temp is 68-93 degrees F and its never been lower than 71. I’ve tried aerating again, I’ve tried mixing to re-suspend the yeast. I’ve got nearly $200 in the mash bill so hoping this isn’t ruined.
Thanks for any suggestions!!

 

[IslandLizard]

Current SG 1.090

What instrument are you using to measure gravity?

 

[TheGad]

What instrument are you using to measure gravity?

Hydrometer.

 

[doug293cz]

What was in your mash bill? If it was heavy on sugar, and light on grain, you may be short of nutrients that the yeast need to stay healthy. I'm not an expert on nutrient requirements - just know that it can be important.

Brew on

 

[IslandLizard]

Hydrometer.

Darn! I was hoping you would say "refractometer" without using a correction for alcohol presence.

Any clue what the theoretical gravity of the mash could/would have been, based on your fermentables and volume? Could it be high enough to cause "cell shock" due to extreme gravity?
Did you add enough nutrients, and the right ones? Lack of those could cause stalling.

 

[TheGad]

What was in your mash bill? If it was heavy on sugar, and light on grain, you may be short of nutrients that the yeast need to stay healthy. I'm not an expert on nutrient requirements - just know that it can be important.

Brew on

i used 128oz of blackstrap molasses, 5lbs of cane sugar, 1lb brown cane sugar, 1 squeezed lemon, Fermax Yeast Nutrient (food grade urea and diammonium phosphate), filtered water, still spirits rum yeast.

 

[TheGad]

Darn! I was hoping you would say "refractometer" without using a correction for alcohol presence.

Any clue what the theoretical gravity of the mash could/would have been, based on your fermentables and volume? Could it be high enough to cause "cell shock" due to extreme gravity?
Did you add enough nutrients, and the right ones? Lack of those could cause stalling.

I don’t have a clue what the starting gravity could be. My fermentation vessels are only 5 gal each. I mixed all together in a 20 gallon vessel, then Divided it into each fermenter vessel. So it’s a literal shot in the dark. I used Fermax Yeast Nutrient (food grade urea and diammonium phosphate) for the nutrients. All 3 fermentations vessels have stalled.

 

[doug293cz]

I don’t have a clue what the starting gravity could be. My fermentation vessels are only 5 gal each. I mixed all together in a 20 gallon vessel, then Divided it into each fermenter vessel. So it’s a literal shot in the dark. I used Fermax Yeast Nutrient (food grade urea and diammonium phosphate) for the nutrients. All 3 fermentations vessels have stalled.

Do you have an estimate of the total liquid volume in all three fermenters? Was the 128 oz of molasses by weight or fluid oz?

Brew on

 

[TheGad]

Do you have an estimate of the total liquid volume in all three fermenters? Was the 128 oz of molasses by weight or fluid oz?

Brew on

I used 10 gallons of water and now have roughly 13ish gallons of mash.

 

[TheGad]

128 fluid oz

 

[doug293cz]

Ok. 128 fl oz is 1.0 gal of molasses. Blackstrap has a specific gravity of ~1.475, and is about 89 wt% sugar, so the equivalent sugar weight is 8.33 lb/gal[water] * 1.475 * 0.89 = 10.9 lb. That makes your total sugar weight in the wash 10.9 + 5 + 1 = 16.9 lb. Sugar has an SG potential of 46.2 pts/lb, so your total gravity points are 16.9 * 46.2 = 781. 781 points in 13 gal of liquid gives you a starting points per gal of 781 / 13 = 60 pts/gal, which is equivalent to a starting SG of 1.060. Therefore, your current hydrometer reading of 1.090 has to be in error.

Doing a more rigorous calculation (using water and sugar weights rather than points) gives a starting specific gravity of 16.67°Plato, or 1.068. Your actual wash volume back calculates to 11.42 gal (assuming your starting water volume was 10 gal.)

Brew on

 

[TheGad]

Ok. 128 fl oz is 1.0 gal of molasses. Blackstrap has a specific gravity of ~1.475, and is about 89 wt% sugar, so the equivalent sugar weight is 8.33 lb/gal[water] * 1.475 * 0.89 = 10.9 lb. That makes your total sugar weight in the wash 10.9 + 5 + 1 = 16.9 lb. Sugar has an SG potential of 46.2 pts/lb, so your total gravity points are 16.9 * 46.2 = 781. 781 points in 13 gal of liquid gives you a starting points per gal of 781 / 13 = 60 pts/gal, which is equivalent to a starting SG of 1.060. Therefore, your current hydrometer reading of 1.090 has to be in error.

Doing a more rigorous calculation (using water and sugar weights rather than points) gives a starting specific gravity of 16.67°Plato, or 1.068. Your actual wash volume back calculates to 11.42 gal (assuming your starting water volume was 10 gal.)

Brew on

Awesome. I’ll go back and measure SG again and let ya know what I get.

 

[TheGad]

Awesome. I’ll go back and measure SG again and let ya know what I get.

So I must have misread? It’s at 1.000. So it’s done. My next question, 32 hours seems like a short fermentation period does it not?

 

[IslandLizard]

So I must have misread? It’s at 1.000. So it’s done. My next question, 32 hours seems like a short fermentation period does it not?

That's a huge difference! Did the hydrometer perhaps bottom out at your previous reading?
How sure are you it's indeed at 1.000?
You can taste some, it should not be sweet at all, anymore, while smelling and tasting very alcoholic. With @doug293cz's calculations that should bring your ABV at around 9%.

I'm not familiar with that specific yeast. Regardless, it's quite short, yes.
I'm guessing a good sized yeast pitch and high(er) ferm temps can do that.

 

[TheGad]

That's a huge difference! Did the hydrometer perhaps bottom out at your previous reading?
How sure are you it's indeed at 1.000?
You can taste some, it should not be sweet at all, anymore, while smelling and tasting very alcoholic. With @doug293cz's calculations that should bring your ABV at around 9%.

I'm not familiar with that specific yeast. Regardless, it's quite short, yes.
I'm guessing a good sized yeast pitch and high(er) ferm temps can do that.

Yea I didn’t take the initial reading. Imma pretend like that didn’t happen. Lol.

So the yeast comes in individual packages and say “up to 6.6gal”. Maybe pitching the whole pack on 4gals accounts for the super seed? Idk. It doesn’t smell sweet. Smells like a cheap wine or something along those lines.

 

[doug293cz]

So I must have misread? It’s at 1.000. So it’s done. My next question, 32 hours seems like a short fermentation period does it not?

There should be very little that is unfermentable in your wash, so I would expect your SG at end of fermentation to be less than 1.000, since alcohol has an SG of only 0.791. A 10%ABV solution of alcohol and water has an SG of 0.986 - 0.987.

Brew on