Sciencemadness Discussion Board

A dilemma with molasses and pH control

CocoMoco - 26-5-2020 at 20:35

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,

ThoughtsIControl - 17-6-2020 at 08:16

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

Sulaiman - 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]

SWIM - 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]

ThoughtsIControl - 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

G-Coupled - 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]

CocoMoco - 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!

oberkarteufel - 27-8-2020 at 02:50

Hello CocoMoco, I know it's probably too late, but I would like to know something about your process (English isn't my first language so maybe I'm missing something).
You stated that
Quote: Originally posted by CocoMoco  
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.
and later you mentioned that raising the pH produces unwanted aromas.

So how actually it was established that pH of 6 is optimal?
Is it taken from some external source? If yes, is it really credible? If it's from your own research - why it is not possible to reproduce it with the same procedure? I'd be thankful for the answer.

I suspect that you're right that off-flavors at higher fermentation pH is caused by some amines. The higher the pH, the more volatile they are; as
lower fraction of it is "bound" in a salt form. Maybe this particular molasses has a high content of amine precursors and is not suitable for fermenting at higher pH?

OR - how about raising the pH, fermenting the molasses and then, once fermentation ceases (and yeasts are dead anyway so they don't give a damn about the osmotic pressure) acidify it to let's say 4,5? This should somewhat suppress volatility of amines.

On an unrelated note, to strengthen the aroma a following way should work (worked with apples for me, so why not with the molasses?): the distillate can be mixed with molasses (pH could also be adjusted). Such mixture could be macerated for some time first or distilled again right away.

macckone - 27-8-2020 at 08:33

I use an acid mix with sodium bicarb to balance the pH.
The mix is citric, lactic and malic acid.

Sodium citrate will buffer the solution.
In molasses aconitic acid is the primary acid.
It is tribasic, similar to citric acid.

Calcium carbonate seems to be the best alternative if your yeast are sensitive to osmotic pressue.
Iron oxide is another alternative.
Both will sequester the acid while remaining relatively insoluble.

I use a mix of blackstrap molasses (ph between 5.6 and 6), brown sugar and white sugar.
The pH of the molasses you are using is pretty low.
Calcium carbonate and iron oxide should bring the pH back up.
Molasses is usually high in iron and calcium so these two should work better than sodium bicarb.

densest - 1-11-2020 at 21:37

You have an interesting problem!
This is to make something to be distilled?

If you haven't found a solution yet I have a few thoughts.

The suggestion of binding the acids sounds fruitful.
pH 5 or less is pretty acid for molasses. Is this "sulfured" molasses with SO2 added?
Buffering compounds like multifunctional organic acids and bicarbonates mixed with strong bases might force the pH to something useful.

Fermentation at pH 6 seems high. 5.4 - 5.6 is what I've dealt with. Stressing yeast can make a lot of different flavors.
There might be a different yeast strain which would produce the flavors you want at a lower pH. There are hundreds of new ones available every year.
Have you talked to people like White Labs?

If osmotic pressure is a problem have you tried diluting your wash? Over density 1.1 most yeast are unhappy. Dilution could (slightly) raise the pH. If this is for distillation dilution might cause other problems.

There's a fair amount of literature about yeast metabolism and flavor compound production. An author named Fix wrote a lot about beer fermentation which might apply.

I made sake for a while. To suppress off flavors I found that adding simple nutrients reduced the amount of other compounds the yeast ate and thereby reduced the objectionable flavors while still getting pleasant ones. Molasses has quite a few nutrients already so that might not work.

Best of luck! It would be informative to know what results you get.