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Hi Guys,

I've got myself a stuck fermentation and I'm looking for some suggestions. My fermentation situation was/is not exactly optimal from the beginning but I'm working with what I've got and trying to make it happen. Now for the info-dump:


4 fermentors. All with nearly identical specs (I will give metric ranges for simplicity) 3/4 have stalled.

1300 gallons of wash in each. Each tank was filled ~650gal, given 10 days, then topped off. (I know this was not optimal)

All washes began between between 1.083-1.087.

All washes fermented out to approx 1.006 before the fermenters were topped off to 1300 gallons. 

Each 750 gal batch consisted of:

600 gal Water
1666 pounds Light Brown Sugar
7.12 pounds DAP
100 gal rum backset
200 gal Voss Kveik/Yeast Slurry
Each batch was sent to the fermenter at 95-97F

I am fermenting in non-jacketed plastic tanks, so no heating/cooling. 

2 of the ferments have now stalled at 1.022 and one has stalled at 1.015. 

 

The part that get me scratching my head is that all of the tanks did just fine with the first ~650 gal, humming right along no problems. I would consider flocculation, however all of the second-fills were done from the bottom port so yeast would have been stirred up.

Thanks in advance for any ideas/fixes.

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That's a high abv but not sky high by any means.

Why did you top it off with more water and re-oxygenate the wash after it was almost done?

What's the purpose of the mash?  It it supposed to be a rum or something using light brown sugar?  That won't have much molasses in it at all.

What was the pH before pitching yeast?

What is the pH currently and what's the temperature?

Where did this Yeast Slurry come from?  Why did you use so much? What is in it?

5 Liters of yeast would easily do that size batch as Kveik yeasts do very well under pitched.

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19 hours ago, JustAndy said:

200 gal of yeast slurry seems insane to me, where is it coming from? Did you measure the pH throughout the process ?

It was absolutely heavy, but I had no data on yeast health or what specific steps were taken during the step-up process so I was very concerned about under-pitching, particularly at 1.085. Unfortunately no pH; When I took over fermentation management the pH meter available to me was broken so only got one (very questionable) reading from 2 tanks early on in the first fermentation both of those were around 3.5 so I cut back on my backset in the second-half fills (first fills had closer to 250gal per 750gal batch). I'm definitely flying blind on that and it's really something I want to get nailed down.

 

17 hours ago, DrDistillation said:

That's a high abv but not sky high by any means.

Why did you top it off with more water and re-oxygenate the wash after it was almost done?

What's the purpose of the mash?  It it supposed to be a rum or something using light brown sugar?  That won't have much molasses in it at all.

What was the pH before pitching yeast?

What is the pH currently and what's the temperature?

Where did this Yeast Slurry come from?  Why did you use so much? What is in it?

5 Liters of yeast would easily do that size batch as Kveik yeasts do very well under pitched.

It wasn't topped off with more water, it was topped off with another 650 gal of wash. Basically:

Day 1) 650 gal wash into empty tank
10) Gravity reaches 1.006
11) Top off tank with 650 more gallons of 1.085

This was realistically just poor production scheduling, but I got pulled by the owners into non-production/Re-opening things so this timetable process won't happen again. 

The purpose is to make.... well, I'm not entirely sure, tbh. The term rum has been floated around a lot but I think some of it will be a very light white rum and some will be re-distilled into a sort of vodka. Rum in name but not really in character.

Questions about pH are unfortunately unanswerable other than 2 questionable readings coming in around 3.5. The meter that I was provided early on in this whole process was largely broken and useless. I've got another one on order so, again, going forward this wont be an issue. Temperature is sitting at approx 80F. Colder than my pitch of 97, but it has now been almost 15 days since the second fill so this is to be expected. 

The slurry was stepped up from an unknown number of homebrew Omega Voss packets. This was all done before my time so the process and timetable is/was unknown to me.  For lack of these metrics as well as an unknown viability/cell count, I intentionally went heavy. I have to assume that the starters that the yeast were in consisted of the same brown sugar that were used for the wash although this is totally an assumption. 

 

 

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Hard to know what to say except to check the pH and see if it needs to be raised.

That 200 gallons of yeast slurry per batch sounds way over the top.  What "constitutes" slurry.  You could just have a lot of unfermentables in your wash due to this and the SG won't drop.

Something I'd suggest doing is a small test.  Make a batch in a single 5 gallon carboy or two and pitch a small measured amount of this yeast slurry to see how it works and how much is actually needed.  Try two tables spoons and see how fast this kicks off.

Have you tasted the wash?  Still sweet or dry?

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22 minutes ago, DrDistillation said:

Hard to know what to say except to check the pH and see if it needs to be raised.

That 200 gallons of yeast slurry per batch sounds way over the top.  What "constitutes" slurry.  You could just have a lot of unfermentables in your wash due to this and the SG won't drop.

Something I'd suggest doing is a small test.  Make a batch in a single 5 gallon carboy or two and pitch a small measured amount of this yeast slurry to see how it works and how much is actually needed.  Try two tables spoons and see how fast this kicks off.

Have you tasted the wash?  Still sweet or dry?

 

I'm all for questioning the "slurry". I've been questioning it since day one, however the fact that it was able to ferment 650 gal of 1.085 right down to 1.006 tells me that there is only, at max, 6 points of truly unfermentable sugars/materials in the recipe. I notice now that I didn't mention my Amlyase  addition but I threw in approx 300mL of enzyme to each 1300 batch (150mL per turn at 130F). This alone should be enough to break down any higher-order sugars/starches. 

The taste of all 4 batches is still a little sweet but not syrup-y. Theyre definitely foamy from fermentation so gravity isnt deceptive, but there is absolutely some sugars left.

I'll check the pH as soon as I have the ability and if that's the culprit I'll make a chalk slurry and pitch that in. If pH is not the issue, is there any consensus on just adding something like a champagne yeast to finish the last 20 points? If this is going to be distilled into a vodka product, I can't imagine it would cause too much issue (but I know those can be famous last words).

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19 minutes ago, Musicman9492 said:

I'm all for questioning the "slurry". I've been questioning it since day one, however the fact that it was able to ferment 650 gal of 1.085 right down to 1.006 tells me that there is only, at max, 6 points of truly unfermentable sugars/materials in the recipe

That's only true if the yeast slurry and the rum backset were the same, since the additions happened 10 days apart I would question that they were from the same batch. If the slurry was just sitting for 10 days, it's likely to be less healthy / have lower vitality and cell count. The backset could also be from the top of the tank (clearer) vs bottom of tank and sludgier with more unfermentables, ash, etc that skew your readings. 1.085 to 1.015 is 80+% attenuation which is what Omega lists the yeasts specs as,  and it might have died out earlier in the 2nd batch from the combination of less viable slurry and damage from starting fermentation in 5% abv medium with a crashed pH. 
 
I wouldn't be concerned about the flavor contribution of champagne yeast at this point, I would be more worried about spoilage from the incomplete ferment sitting. If you add champagne yeast I would check out scott labs helpful guide, as it's a pretty harsh environment to pitch yeast into https://scottlab.com/restart-stuck-fermentations

hindsight is 20/20 but it would have probably worked a lot better to combine your 4 ferments into 2, and then started 2 new ferments. 

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3 minutes ago, JustAndy said:

That's only true if the yeast slurry and the rum backset were the same, since the additions happened 10 days apart I would question that they were from the same batch. If the slurry was just sitting for 10 days, it's likely to be less healthy / have lower vitality and cell count. The backset could also be from the top of the tank (clearer) vs bottom of tank and sludgier with more unfermentables, ash, etc that skew your readings. 1.085 to 1.015 is 80+% attenuation which is what Omega lists the yeasts specs as,  and it might have died out earlier in the 2nd batch from the combination of less viable slurry and damage from starting fermentation in 5% abv medium with a crashed pH. 
 
I wouldn't be concerned about the flavor contribution of champagne yeast at this point, I would be more worried about spoilage from the incomplete ferment sitting. If you add champagne yeast I would check out scott labs helpful guide, as it's a pretty harsh environment to pitch yeast into https://scottlab.com/restart-stuck-fermentations

hindsight is 20/20 but it would have probably worked a lot better to combine your 4 ferments into 2, and then started 2 new ferments. 

Hindsight is definitely 20/20 in a lot of this situation. After getting this situation under control I'll be starting fresh with everything so that level of control will be very, very important.

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3 minutes ago, JustAndy said:


hindsight is 20/20 but it would have probably worked a lot better to combine your 4 ferments into 2, and then started 2 new ferments. 

Two schools of thought on that.  Some people actually keep ferments going on for many generations never taking more than 2/3 so the yeast stay alive to work the next batch.

Other school of thought says if you have 2 smaller batches underway and plan on doing more combine the first 2 first so they will finish giving you something to run while the other ferment and finish a day or two later.  This will require more yeast but if you manage yeast it's not a problem.

People do both methods and I'd imagine you will get slightly different tasting mash/wort this way as well (good or bad).

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1 minute ago, Musicman9492 said:

Hindsight is definitely 20/20 in a lot of this situation. After getting this situation under control I'll be starting fresh with everything so that level of control will be very, very important.

Yea and when you get time try a small 5 to 10 gallon ferment to see how much actual yeast slurry you actually need.  Kveik yeast is known to like being under pitched compared with other common yeasts so you may not be doing yourself any favors over pitching it which it sounds like.

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1 minute ago, DrDistillation said:

Yea and when you get time try a small 5 to 10 gallon ferment to see how much actual yeast slurry you actually need.  Kveik yeast is known to like being under pitched compared with other common yeasts so you may not be doing yourself any favors over pitching it which it sounds like.

Yeah, I've been in contact with Richard Priess from Escarpment Labs and have also used Voss in my beer brewing days so I've got the basics down, I just had some serious concerns about overall viability so went a little overboard.  

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All sugar washes here. l For me, 80 degrees would all but stall a ferment but I am using a different yeast than you. Also, ph below 4 can be a problem as well. Hard to tell how much it has fallen since you were last able to measure it. Hopefully you get a meter quick.

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