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Submitted to start a discussion as I don't know if what I think is true: (I was going to post this in Der Wo's Rum thread, but I figure it would take the thread too far off topic.)

So thinking about the composition of the dunder pit, what it does, and how it is used, I question the idea that the dunder itself adds significant esters to a fermentation. My belief is that the dunder creates a feedstock for esters, but it does not necessarily add significant amounts of esters by itself.

Based on our collective research into the areas of dunder pits and ester formation I think the consensus is that dunder pits do contain esters. My belief is, though, that the mechanism for the majority of ester development is from the feedstock of carboxylic/fatty acids and catalytic acids present in the dunder. The catalytic acids form from bacterial activity that feed on unfermented longer chain sugars. Carboxylic/fatty acids form from the base feedstock (molasses/grains/etc) and from yeast autolysis. When added to a fresh wash/wort, the dunder creates a low pH environment and also nutrition (fatty amino acids from the yeast autolysis/base feedstock, other minerals) for the growing yeast. The excess carboxylic acids, catalytic acids, and the newly formed alcohol from the yeast react to form esters. In the dunder there isn't a large supply of alcohols and I think that it would limit the ability of esters to form.

Thoughts? Can a dunder pit add flavor by other means? I'm assuming yes, but am not sure what that piece is.

Commercial distilleries normally strip all the alcohol out of the wash, so there is no alcohol left in the dunder or backset normally. And no fermentable sugars, which could get fermented into alcohol, normally. No alcohol in the dunder -> no esters in the dunder.
"Feedstock" sounds for me like nutrients. But it's not my language. I would say the bacterial produced acids in infected dunder are "elements" for esters.

But in original dunder pits is not only dunder but also sugar cane trash, which has fermentable sugars. Because of that there will be a low alcohol content formed by wild yeast and then a few esters. But not many, because the lower the alcohol content the lower the esterification speed. And there is not much time, because this alcohol will soon get fermented to vinegar.

But simply add dunder to alcohol (wash or low wines) and you will get the esters.

Here cane trash is mentioned:
http://cocktailwonk.com/2016/03/days-of ... dient.html" onclick="window.open(this.href);return false;" rel="nofollow

Well isn't that interesting:

Vivian told us the ooze is called muck— a giant bolus of bacteria that creates a soup of carboxylic acids.

1. So we're actually talking muck pits.
2. "Soup of carboxylic acids" - I love the sound of that.

Thanks Der Wo!

Single Malt Yinzer wrote: 2. "Soup of carboxylic acids" - I love the sound of that.

Thanks Der Wo!

The irony is that der wo regularly apologizes for his English while simultaneously being one of our best writers.

When we talk dunder pits, we are talking about recent hobbiest inventions concocted from sparce info and rumours. You need both muck and trash pits to simulate what happens in the industry, and you need to know how to use them, and they ain't telling.

NZChris wrote:we are talking about recent hobbyist inventions concocted from sparce info and rumours.

And that's why I'm trying to figure out the facts & science behind them. I agree, most of what people post about dunder/muck/junk is well, junk.

I will tell you just what I know about this so far:

Dunder is the acidic byproduct of fermentation by yeast which has various leftover micronutrients provided by dead, autolyzed yeast and other matter. There are, in fact, some sugars left. They are mostly polysaccharides. Some yeasts and strains of fungi (e.g. aspergillus) will break them down and produce their own byproducts in the process.

I have read about strains of clostridium too being important in rum. While I don't doubt they can be found in rum dunder, but they would not be the dominant strain at the typical pH of spent rum wash which is well below 4.6.

Instead, gram positive, anaerobic bacteria grow in great numbers (mostly lactobacilli) and produce lactic, acetic and other short chain carboxylic acids. This lowers the pH even more.

During distillation and aging these acids will be converted to esters, the chemistry of which has already been discussed at great length on this forum.

The other possibility is maillard because of the constant contact of b-vitamins, amines, etc from decayed microbes; but again very unlikely due to a low pH.

I read somewhere that esters were created when the muck and the vinegar from the trash cistern were mixed to make the essence to go into the ferment. I've only tried it once, but it was so bloody awful I couldn't bring myself to put it into the large ferment I had going at the time. Next time, I'll split off a still charge worth of ferment and add some essence to that.

raketemensch wrote:
The irony is that der wo regularly apologizes for his English while simultaneously being one of our best writers.

+1.

MDH wrote:I have read about strains of clostridium too being important in rum. While I don't doubt they can be found in rum dunder, but they would not be the dominant strain at the typical pH of spent rum wash which is well below 4.6.

This is why the pH has to be raised to around 5.5. Then it's very easy to get the butyric esters from clostridia. Much more easy than to get lactic esters, because butyric esters are more volatile (at least according to my experiments).

NZChris wrote:I read somewhere that esters were created when the muck and the vinegar from the trash cistern were mixed to make the essence to go into the ferment. I've only tried it once, but it was so bloody awful I couldn't bring myself to put it into the large ferment I had going at the time. Next time, I'll split off a still charge worth of ferment and add some essence to that.

Did you put the dunder in before or after fermentation? If before, then the ugly smell will change during fermentation. If after, it should smell better very fast. To put it in after is much more informative.

Fresh dunder went into the ferment.

The essence I made was from my muck and my cane vinegar that was started several months earlier. It was so foul that I did not want to risk ruining a large and expensive ferment of was shaping up to be a very nice rum by adding that stinking crap to it. I have smaller stills now that can be used for small batches that won't be a great loss if they don't work out, so I'll start another muck hole when I do my next rum, using starter cultures and monitoring the pH instead of leaving it to its own devices. I still have the trash pit vinegar.

2 great reads:
http://cocktailwonk.com/2016/03/days-of ... dient.html" onclick="window.open(this.href);return false;" rel="nofollow
https://www.bostonapothecary.com/muck-h ... under-pit/" onclick="window.open(this.href);return false;" rel="nofollow
Personally I think (not from direct experience) that yeast are an important ingredient of the muck pit that could be missed at the hobby level. Most commercial washes are yeasty, most hobby washes are clear. This means hobby dunder has less/no boiled lysed yeast, as most of us leave that behind in the fermenter and reuse or trash it. Note Hampden Estates specifically adds any settled yeast to their muck, both settled from ferments and settled from dunder. I suspect the yeast serves as food for the bacteria. I can somewhat laboriously understand chemistry but don't know it well so I've been meaning to look at the chemical makeup of yeast, like its amino acids to see if yeast can serve as a chemical feedstock directly for ester or higher alcohol production in the muck.

Also, while dunder is 0% etoh, it may well have appreciable amounts of higher alcohols which would be feedstock for esters to form IN the muck pit. Presumably these higher alcohols would build up if recycling dunder.

So I'd guess that we KNOW muck makes feedstock for esters, but it's at least possible that some esters form in it. Especially non-ethanol esters. Or small amounts of ethanol esters at the hobby level where we don't always strip to 0% etoh.

I would have thought most hobbiests would run dirty because it is so hard to clear. I've never run clear rum wash.

My dunder SG is around 1030, so there is a lot of food for something in it. I've never rechecked the SG of the hole to see if it dropped, which is a bit foolish of me.

True, although while maybe not really clear, I've usually had a good bit of sediment that stayed in the fermenter, and never gave it a thought until recently and definitely plan to save it now. Or now that I have a steam kettle just ferment and run on all the yeast and make sure all dunder sediment gets in the pit.

raketemensch wrote:

Single Malt Yinzer wrote: 2. "Soup of carboxylic acids" - I love the sound of that.

Thanks Der Wo!

The irony is that der wo regularly apologizes for his English while simultaneously being one of our best writers.

I think he might have a bit harder accent but his english is perfect I also enjoy his writing.

PapaPro

papapro wrote:

raketemensch wrote:

Single Malt Yinzer wrote: 2. "Soup of carboxylic acids" - I love the sound of that.

Thanks Der Wo!

The irony is that der wo regularly apologizes for his English while simultaneously being one of our best writers.

I think he might have a bit harder accent but his english is perfect I also enjoy his writing.

PapaPro

+100
Der wo explains his processes very well, he's helped me tremendously in my infections and dunder pit uses.

IMHO I think using all the crap in the fermenter helps once boiled in the still and also increases the food supply for the dunder pit to live a happy, funky life.

My biggest learning curve was learning how to maintain the pH to make it thrive, 5.5 keeps the pellicle on top and if maintained will stay there until it drops to around 4.5 or less or above 6.2 so anywhere in the 5's is helped me keep an active pit.

I let the pH drop, the pellicle falls then the aging process begins. I periodically feed the pit with raw dirty potatoes and use pickling lime to raise the pH back to mid 5's and start over again, not sure if this is increasing the good stuff or not but this is the newest experiment I'm playing with and also to keep the chance of it breaking down to ammonia due to the organics in the pit.

Shine0n wrote: I let the pH drop, the pellicle falls then the aging process begins. I periodically feed the pit with raw dirty potatoes and use pickling lime to raise the pH back to mid 5's and start over again, not sure if this is increasing the good stuff or not but this is the newest experiment I'm playing with and also to keep the chance of it breaking down to ammonia due to the organics in the pit.

You have the distiller's version of a chia pet. .