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Author: Subject: A dilemma with molasses and pH control
CocoMoco
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[*] posted on 26-5-2020 at 20:35
A dilemma with molasses and pH control


I've been working as a fermentologist for a couple years now exploring yeast fermentation of molasses. The absolute best aroma and resulting flavor occurs when the pH of the molasses wash is close to 6 throughout the ferment with a particular kind of yeast. Raw molasses often has a resting pH between 4.7-5.3, which needs to be brought up to the optimal pH range.

The biggest problem facing this process is the creation of off-odors when raising the pH with an excess of strong base, such as calcium hydroxide. Calcium hydroxide is used to both raise the pH and help precipitate some of the ash and gunk that remains in suspension in molasses (which is then removed with a centrifuge - thinning this out helps the yeast to ferment all the sugars. Use of other salts, such as sodium or potassium, further contributes to the osmotic pressure which will stress the yeast). I can usually only bring the pH up by 0.5 before off-odors start to develop, which I believe occurs from reaction of the strong base with nitrogenous compounds in the molasses. For low pH molasses, this makes it hard to reach the optimal fermentation pH.

Some treatment with strong base is desirable, as it cleaves the glycosides that lock away the aroma precursors. However, it can only go so far and then I have to find some other way to reach high pH without ruining the molasses, antagonizing the yeast, or creating off-aromas.

Addition of ammonium hydroxide has been attempted thoroughly, though this has problems, namely with over accumulation and the potential creation of high amounts of ethyl carbamate (the yeast will eat it when growing, though if an excess remains it can ruin aroma in the distillate and/or contribute to an accumulation of ethyl carbamate through reaction with carbon dioxide and ethanol).

Does the biochem community have any creative ideas for increasing the pH without increasing the osmotic pressure or adding an excess of strong base? I would be deeply indebted to anyone with good advice.

Thank you,
Coco
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ThoughtsIControl
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[*] posted on 17-6-2020 at 08:16


Do you have a video of this procedure? Very interesting problem



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Sulaiman
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[*] posted on 17-6-2020 at 08:42


Have you tried an excess of calcium carbonate (lime, chalk, marble, seashells)?

Crushed seashells in a sock is common amongst amateur brewers, at small scale.

[Edited on 17-6-2020 by Sulaiman]




CAUTION : Hobby Chemist, not Professional or even Amateur
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SWIM
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[*] posted on 17-6-2020 at 09:18


I wonder if ion exchange resins would work in such an environment?

A weak basic resin perhaps.
like polyethylene amine.

I know little about these resins, but they certainly do seem to satisfy some of your requirements.
Insoluble, weakly basic. And reusable.

So I suppose your pH is probably changing constantly during the fermentation period from CO2 unless you add enough base to handle that.
Do you add base in repeated small doses to maintain the high pH or are you just giving it one dose, in which case buffering might be important to consider.

EDIT: So I picture these unpleasant odors as being a bit like Marmite.






[Edited on 17-6-2020 by SWIM]




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This sounds like the best idea since putting ortho tricresyl phosphate in Ginger Jake.
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ThoughtsIControl
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[*] posted on 18-6-2020 at 11:38


"I wonder if ion exchange resins would work in such an environment"

After trying to figure out what an ion exchange resin is, I was led to discover how a water softener works. Haha!
So it's the same thing as column chromatography basically? Stick some substrates on beads and separate your mixtures based on size and affinity?

Also, Marmite isn't very pleasant in my opinion




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G-Coupled
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[*] posted on 18-6-2020 at 12:18


Quote: Originally posted by ThoughtsIControl  
...Also, Marmite isn't very pleasant in my opinion


It tastes a *lot* better than it smells IME. :)

Also - use very sparingly - it's not Nutella.

[Edited on 18-6-2020 by G-Coupled]
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CocoMoco
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[*] posted on 20-6-2020 at 08:55


Just noticed all the replies, thank you all for your thoughts!

The bad smells might have to do with creation of compounds similar to putrescine, cadaverine, and whatever the awful "mouse pee" compound is (I've actually smelled this in the high-boiling fractions of certain rums...). These are also created from boiling the wash without separating the yeast first.

Ion exchange sounds very interesting though I'm also confused by it (my chemistry knowledge is rusty...), would I just pass the molasses over suitable resin beads and they could pull out certain salts/ions? Or, would it be left in the fermentor to act somewhat like an insoluble buffer? Are there any products you might recommend?

A truly stellar remedy would be if I could add the ionic base equivalent of certain weak acids, such as acetate and malate (not the salts), which would also allow me to raise the pH.

Acetic acid is released by the yeast throughout the ferment. I can help to reduce the release with B-vitamins and can precipitate out a portion with calcium carbonate, though I still have to end up invading the fermentor. Calcium acetate precipitate can also spoil the yeast bottom, which we hope to keep pure so that it can be used for other purposes.

Once a certain concentration of acetate is reached, then an equilibrium forms between the acetate being absorbed and released by the yeast, which allows the pH to stabilize. At higher pH levels, it takes more acetate in solution to reach this equilibrium. If I could find a way to add acetate without adding sodium, potassium, calcium, etc. that would be incredible as I could start the ferment with the ideal acetate concentration for pH balance at my desired pH of 6.

The yeast can also convert malic acid to ethanol, causing a pH increase. I've thought about adding malate, though again I often have to add it as a salt which brings an excess of calcium/sodium, etc. which can upset yeast metabolism.

Is it possible to create the equivalent ionic bases of acetate and malate though something like electrolysis?

Thank you all!
~Coco
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