Stalled / Very Slow Fermentation with High Gravity Beer

[mjl3434]

I made a high gravity beer, a Gulden Draak clone, using all grain on the Grainfather G30v3, using untreated Illinois tapwater with a 156 degree F mash. I added 5 grams of yeast nutrient to the wort. The OG was 1.072. I pitched Wyeast 1388 Belgian Strong Ale yeast from a smack pack, without a starter. It did nothing for a day, then had a quick 24 hour fermentation, where the gravity dropped to 1.052. At that point I added a 1lb package of 1.032 ppg dark candi syrup, which should bring the effective OG up to 1.0792. That sugar seemed to ferment through rather quickly but then when I measured the gravity around day 3, it was at only 1.052 again. It kept bubbling very slowly through the air lock. I added some yeast energizer and gave it a little shake, that temporarily sped things up but not much. A week in I measured the gravity and it was still 1.052.

At that point I decided to call in the big guns and ordered two smack packs of Wyeast 3787 Trappist high gravity yeast packs, and a 1/4 lb of DME. I created a starter using the DME. I could not get my new magnetic stirrer working due to not having any flat enough fermentation vessels. So I noticed that the starter had fermented through overnight and the yeast was at the bottom. No worries, that small amount of alcohol should not kill two whole smack packs of alcohol tolerant yeast. I then racked the beer to another carboy to get it mostly off the lazy Wyeast 1388, and pitched the yeast. It slept for a little bit but later in the day was fermenting. About 24 hrs later it too slowed down, and I measured the gravity. Now it's at 1.050. Two huge packs of alcohol tolerant yeast and it only ferments 0.002 points?

At this point I am out of ideas, other than it possibly being the ambient temperature too low. It's fermenting in my basement which is chilly, perhaps 60F, or even in the 50s at night.

Am I going crazy here or shouldn't this thing ferment more quickly? It spent 11 days on the first yeast and is 30 hours into the second yeast. What would you do here to get this thing to finish fermenting?

Is it possible it's almost out of sugars but still reading a high gravity? Should I just pitch wine yeast or something even stronger?

I am hoping for 9-10% ABV which requires finishing at 1.010 - 1.000.

 

[Bobby_M]

Right off the bat, you should know that one smack pack of yeast is not even close to enough under almost any circumstance. Couple that with the likelihood of the pack being some age greater than zero, the viability is even more impacted. Those packs start out as a 100B cells and drop about 20% per month. A 1.072 OG needs about 400B cells of yeast, or FOUR fresh packs. If the packs were 2 months old, you'd need 7.

Second. Belgian beers should be mashed at 149-152. You may have a lot of unfermentable dextrines due to the higher mash temp.

Belgian beers are generally pitched at about 68F and allowed to free rise during fermentation which can get them into the low to mid 70's. The main thing though is to not allow them to cool off until well into the expected final gravity. You can't ferment either of those yeast varieties at 50-60F. You need a warmer room or a heat pad and controller.

 

[mjl3434]

Thanks that’s all useful information. I knew a higher mash temperature would cause less fermentable sugars but I wasn’t aware sugar a small variation could make such a big difference. Is there a way to calculate an estimate of the final gravity assuming a mostly complete fermentation?

Also what should my next steps be? I moved it to my second floor so now it’s comfortably in the 70s. It’s still bubbling slowly. Should I purchase and pitch even more yeast? 1.050 is like the gravity many beers start with.

 

[Bobby_M]

Thanks that’s all useful information. I knew a higher mash temperature would cause less fermentable sugars but I wasn’t aware sugar a small variation could make such a big difference. Is there a way to calculate an estimate of the final gravity assuming a mostly complete fermentation?

Also what should my next steps be? I moved it to my second floor so now it’s comfortably in the 70s. It’s still bubbling slowly. Should I purchase and pitch even more yeast? 1.050 is like the gravity many beers start with.

I think warming and rousing the fermenter to get the yeast back up into the beer would help.

 

[G_robertus]

Mashing too warm won't give you attenuation this poor. I know some brewing software already accounts for it, but I'm not sure all of them do. BrewFather for example does.

I agree you pitched way too little yeast initially though. Both strains can stall I think, so racking and adding in a bit of oxygen during that process could help.
Just to rule things out, how do you measure SG? Hydrometer or refractometer? If it's the latter you need to convert the reading, but it's still quite high (1.036).
Adding wine or champagne yeast typically will do very little. Many cannot ferment maltotriose and some cannot even ferment maltose. Lots of them also produce kill factors that will kill other yeast that isn't resistant, which your strains are not either.

Try racking one more time perhaps and get it as warm as you possibly can. If you want it really dry, consider using amylase or Saison yeast.

 

[mjl3434]

@ G_robertus - I used a hydrometer after the counter flow wort chiller was done, it was at room temperature. I don't have a refractometer.

After moving it upstairs the fermentation temperature gauge has gone up from 72F (in a 60ish F room) to 76F (in a 70ish F room), and the surface looks like a cup of soda fizzing, so I think we're back in business.

Is there a resource that explains the yeast pitching rate? Obviously this is ignorance but I thought 100 billion yeast cells would be plenty, so I'm surprised that I needed 4-7 packs.

 

[day_trippr]

You could play around with a "Yeast Calculator" like this one. It provides a few "pitch rate" options and combined with the other factors will show a recommended pitch and how to get to it given the amount and "creation date" of the yeast on hand. I happen to prefer the 1M cells/ml/°P pitch rate and create starters accordingly. For my typical 11 gallons of ~1.070 OG wort to the fermentors that means roughly 350B cells per 5.5 gallons...

https://www.brewunited.com/yeast_calculator.php

Cheers!

 

[G_robertus]

There are numerous sources on yeast pitching rates and the likes online. Wyeast has their own post on it. Typically less yeast causes stress and slower fermentation. The reason it could stall is that some yeast, including some Belgian yeasts, tend to stop fermenting when the temperature drops too much below a certain temperature. I don't recall whether this was the pitching temp or just some number. Without temperature control, the wort temperature will decrease as fermentation goes on therefore fermentation will stall.

Pitching in a stressful environment will decrease cell counts even further and they can become exhausted over time. Sometimes fermentation will continue, but incredibly slowly since there aren't enough cells.

 

[IslandLizard]

I didn't see you mentioning oxygenation/aeration of the wort.
Aside from using ample healthy yeast (from a fresh starter), good oxygenation (or thorough aeration) when pitching the yeast is also necessary, even more important with higher gravity worts, like yours.

When fermenting high gravity beers a 2nd oxygenation (or aeration) is often recommended. It's to be done 12-18 hours after the first oxygenation and pitching the yeast, but before active fermentation has started (e.g., krausen forming). So proper timing of the 2nd oxygenation is key.

But you're far past this already, so let's see how we can help you. A 1.080 OG is not crazy high, so there's hope.

After moving it upstairs the fermentation temperature gauge has gone up from 72F (in a 60ish F room) to 76F (in a 70ish F room), and the surface looks like a cup of soda fizzing, so I think we're back in business.

That's a good start, but key is to keep the fermenter warmish, 74-76F and keep that temp constant! A temp drop can (and likely will) stall the yeast at some point before it's finished.

That's why many of us use a dedicated fermentation chamber where we can control the temps 24/365

 

[IslandLizard]

so I'm surprised that I needed 4-7 packs.

No, you'd only need 1 pack. Use a good yeast calculator, and make a starter a few days (or a week) before you brew a batch. You'd pitch that starter which contains ample and very healthy yeast cells.

 

[mjl3434]

@IslandLizard - I applied oxygen for 60 seconds.

I think other than the fermentation temp I'm having trouble figuring out what I did wrong. Now that it's in a warmer room it's going pretty well.

 

[IslandLizard]

I'm having trouble figuring out what I did wrong

Underpitching (1 pack, no starter) and fermenting too cold (60F).

She should be doing better now being in a warmer place (70s F), but may still be short of enough healthy yeast cells.
Let her do her thing for 2 weeks at constant comfy low to mid 70s temps. Not much more you can do.

 

[Bobby_M]

Is there a resource that explains the yeast pitching rate? Obviously this is ignorance but I thought 100 billion yeast cells would be plenty, so I'm surprised that I needed 4-7 packs.

100B cells is enough for SOME wort but not high gravity ones. You don't have 100B cells in the pack unless the package date was "today".

For higher gravity ales, you want about 1M cells per 1mL of wort per degree plato (SG/4 so 1.080 is 20P). 5 gallons is about 19,000mL. So, 19,000 x 20 x 1M = 380B cells. Even if the packs were from "today", you'd need four.


https://www.brewhardware.com/product_p/bookyeast.htm
https://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/
https://www.mrmalty.com/pitching.php
https://yeastman.com/calculator

 

[hottpeper13]

Do it this way. Make a small beer (5 gal) pitch one pack or a small starter then pitch that cake onto the high gravity wort. You have a brew to enjoy while the HG one is conditioning. So simple!