kelbor

Help: Ferment stalled

11 posts in this topic

Hi everybody -

I have my first stalled ferment and am a bit unsure how to proceed.

Back story: Rum wash started on Saturday by me but inoculated by my partner later in the day. Wash is 500 gallons (100 gallons Molasses, 200 gallon rum backset, 200 gallons water). Inoculation consists of several types of yeast hydrated correctly. Wash is pumped into the fermenter from the top so it has plenty of air in it. Yeasty nutrients consists of 540 grams DAP, 70 grams vitamin B complex, 10 grams magnesium sulfate. I took Sunday off and came into the distillery on Monday morning expecting to see a fermenter happily bubbling away like normal but nothing. I tested the numbers and got a PH of 4.68 and brix of 29 (which is a bit high but with the non-fermentable sugars from the backset giving as reading this is pretty much normal for our wash).  I re-pitched another round of hydrate yeast (I wanted to see if the yeast might be dead but the re-hydrating yeast seemed very active).

I came in this morning, Happy Fourth of July by the way, and nothing going on in the fermenter.

Any ideas?

Thanks! K

 

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Forgot to mention - Temps during initial pitch were consistent with previous ferments -Yeast was pitched at 95 F. the first day and 90F the second time. Ferments are held at 90 F as a rule of procedure.

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What is the pH now?

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If the pH crashed you can raise it with calcium hydroxide, but you will probably need to repitch.

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Only thing I can think is that 29 brix seems really high.  It's always tough, as you know, with molasses due all of the unfermentables. What's the spec sheet list the TSAI as on the molasses?  Product we use is listed at between 68 and 72% TSAI.  Regadless, I would have expected to see some activity.  You know your yeast... is 95F too high?  As @stillwagon said, test pH and adjust up w/ CaOH (we've used NaOH in a pinch).  We've been know to pull off a sample and ferment in a 2L erlenmeyer just to find out what works.

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Update:

Last Wednesday i went and picked up 12 packets of EC-1118 and re-hydrated as per directions. After 20 minutes I added the yeast to 5 gallon carboy with a mix of about 50% of the stuck ferment wash (well aerated) to  fresh water. Early batches using the same molasses to water ratios as the stuck ferment (before we had backset available for use) tested out at about 20-21 brix.  I am assuming the Brix of 28 I get now indicates approximately 7 Brix of un-fermentable sugars that came in from the stillage I added. P.H. of the mash still tests 4.65. I forgot to test the PH of the stater liquid i added the re-hydrated EC-1118 to. Brix of starter should be around 20 Im assuming (didn't bother to check since I know the brix of the wash).

Thursday morning I prepare a second 5 gallons of 50/50 water and wash - mix in sterilized vat with the now slowly bubbling starter started on Wednesday. I split into two 5 gallons carboys, aerate and airlock.

Friday afternoon I took the now two fairly active 5 gallon carboys and added them back to our main stuck ferment. I should have maybe grown a bit of a bigger starter but I had a prior commitment I was attending ( a six day festival) and had been driving about an hour each way the last few days to get this starter going and wouldn't be able to return through the rest of the weekend. The starters were active with visual, albeit slow, rolling and vigorous bubbles through the air-locks.

Sunday the ferment was checked and nothing. Sorry for the book but Im pretty stumped. Going in this afternoon after work to check numbers again.... 

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I start at 20 - 22 brix, buffer pH with calcium and keep it at about 5, use plenty of nutrients, keep it 80f or warmer, and never get a stuck fermentation. I do about 500 gallons of wash a week for the last 4 years. So, I would look at it from the beginning: what is your water chemistry? What exactly is your feedstock? How are you adjusting, monitoring, and maintaining pH? What are you using for nutrients? Fermentation temp? Normal finished gravity?

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You know, I kind of just keep doing the same recipe each time and haven't been monitoring things as well as when I began. I do always check PH and Brix and they have stayed consistent. Don't add anything to monitor PH crash because I have been finishing dry tasting after about 7-10 days of fermentation and I end in the low to mid 4's (a bit lower then 5 but not in the dangerous range). I keep ferments at 90 degrees F and have an aquarium pump at the bottom of my fermenter to keep yeast suspended. Yeast food consists of 500 grams DAP, 70 grams Vit B Complex, 10 grams of Epsom Salt dissolved separately and added while initially  aerating the mash in one feeding. I used to add a few pounds of boiled yeast for nutrients and citric acid to bring the PH down but now I just add 175-200 gallons of my backset which should have plenty of acid and boiled yeast in there. Feedstock is 100% black-strap from Glory-bee. I forget what my normal ending gravity is as I have not checked with the meter in a while - its in my notes. I just usually taste a bit of it.   

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I am understanding correctly that this is the first batch you are using backset with? 29 brix is high, even if you think 7 brix of that is unfermentable the density of the wash is very high and the yeast might be experiencing too much osmotic stress. If you have been using backset for several generations, it's also possible that you have accumulated yeast-toxic levels of salts/minerals etc. 

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Hi JustAndy,

I agree, 29 Brix is high. If this was a sugar wash or grain wash it would be ludicrous and just may be with this one as well. When I first started running experiments with different rum washes I found that one gallon of this molasses with four gallons of water gave me about 20-21 Brix. This, of course being a 100% molasses rum wash, did not finish out dry at 0.000 on the hydrometer due to crud and unfermentables in the blackstrap so at 21 brix I was not pushing above 8-9% alcohol. So, I am estimating that there are 8-9 brix points, (sorry, I miss calculated 7 earlier) being brought back over from the pot to the fermenter.

Not first batch with backset (probably at least the 15th) and same amount of everything as usual. It is a lot of osmatic pressure but not out of the range of what we've been doing and I'm not sure how burnt sugars affect osmatic pressure.  I really do feel like you may be onto something with the building yeast-toxic levels of salts/minerals though. It is a lot of backset to add each time.

Update: Just checked ferment. Tank has a white film scum like a bloom on a wine/mead ferment. Smell is rum wash based with a slight sweet acetone/nail polish aroma - exactly like fores actually. I drew liquid from the middle of the tank and it smells just fine - like clean rum wash. PH is 4.44, Brix is 28, temp is 85.

 

Is any body else out there using backset in their rum washes want to chime in on issues they may or may not have had with continued use? Is 200 gallons of backset in a 500 gallon wash too much?

 

Thanks!

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Man I tell you. It seems like I've figured about every way possible to stick a raw brown sugar wash here  

 

Your thing tho I think could be solved on this batch by just watering it down.  

 

Maybe be split and top off or something similar.   Once it's going again you could always add some more fermentables as it proceeds so you aren't wasting distilling time  

 

Seems like Ike a lot of backset.  

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