Dunder Pit Explained: Safe Use, Dosing, and Flavor Impact

Build a pragmatic dunder SOP for craft rum: controlled culture setup, safe process insertion point, and dosing discipline to avoid undrinkable overexpression.

Quick summary

Core principle

Okay, we spoke about the backset cycle. It comes from whisky making and then there is another procedure, another virtuous cycle, number two, which is called Dunder Pit.

Dunder Pit comes from the rum making industry. What do they do in the Dunder Pit?

Basically, you remember that backset, right? So they take backset, but instead of putting it back in the mash, they just put it in a Dunder Pit and they let it sit there and it grows funky and bad and horrible.

Bacterial infections, esterification, more flavor, not by definition better flavor, but interesting flavors at least. And since in rum you don't mash because the sugars are ready for fermentation directly, you can add part of that Dunder Pit with your fermentation, with your molasses, with your water and create more flavors.

Now, I find that an interesting method because the problem with Dunder Pits is, and we'll show you a picture or Google it, is that they're funky, they're full of bacteria. And if you start a fermentation and the yeast needs to create alcohol and flavors, but there's also bacteria, it's very difficult to predict who's going to win.

Sometimes it's going to be one, sometimes the other. Flavor, all flavors, and flavor and alcohol, or maybe no alcohol.

So it's difficult to play with. So my advice has always been don't add the Dunder to your fermentation if you want to make rum, but add it where you decide on flavor.

So before you do your finishing run, add a little bit of Dunder because it's a palette full of, packed with flavors, weird flavors, interesting flavors, bacterial-induced flavors, and you add it before you start your final run. Well, because we are heating up that still, we already made a fermentation, so the alcohol is there, we had a controlled fermentation, so the flavors are there, we add a flavor source, and even if these bacteria think they're going to have fun, well, it's 20-30% strong alcohol, so well, sayonara, motherfuckers.

Or we're going to put it still on, temperature's going to rise, we're going to kill you anyhow, so we don't run any infection risks. We would if we would add the bacteria from the Dunder pit to the fermentation directly.

So add them prior to starting your run. Dunder is basically aged bag set, infected bag set.

The way they do it in the tropics, because this comes from, I would say Jamaica, so heavy rums are really built around Dunder pits, the Caribbean at least. They dig a hole in the ground, and this is the tropics, you make rum and you distill, maybe outside or in a shed, then after the run is done, you open up your still and let everything flow out into that swimming pool size hole.

It's tropics, it's warm, there's all kinds of microbiology living in the ground, in the soil over there, and it starts to get really funky, and after around six, seven weeks, it's ready to have part of it taken out, in this case added to the finishing run, prior to the finishing run, then doing your finishing run, and you create more, harvest more, concentrate more interesting flavours.

How it works in practice

I've been told by Jason that the way they do it in the tropics, you might remember Jason, he worked with us together a lot in the university, from the Virgin Islands, from the Caribbean, loves rum, makes his own rum.

He told me the way they sort of start a Dunder pit over there is, well, they dig that hole, right, and then they sort of fill it up with a first batch of backset that freshly runs from the still, and then as a sort of offering or ceremony, they take a rooster, cut its head off, and throw everything into the Dunder pit, which is, I think, a great way to, well, I don't think, you shouldn't do that, but it's at least a great way to introduce bacteria to your Dunder pit.

So, I remember my question being to Jason, like, in these days of equality, why the rooster?

He said, well, because chickens still lay eggs, so they have a function, and the rooster can just, well, he still has a function, but only in the Dunder pit, right? I thought that was a really funny answer. If you start a Dunder pit, use kefir or yogurt, bacteria that you can buy fresh, and have them start the Dunder pit.

Do it in a controlled environment, so for example in a 55-gallon, 200 liters barrel, plastic barrel, metal drum, outside of your building. You don't want these infections close to your grains, close to your substrates in general, because they can infect those as well. So, maybe you don't want to work with it.

You'd rather stay with the bag set cycle. I did a lot of testing with it. What you need to add to your finishing run, to the boiler prior to starting your finishing run, is maybe one, two, three percent at all.

So, for example you do a 500-liter boiler charge, maybe add five to 15 liters of Dunder. Because if you add more, it overpowers, and this translates to ester, taste molecules. If you compare a Bacardi-style medium rum, it has an ester count of around 30 to 45 parts per million, flavor molecules, parts per million.

If you look at a Jamaican style, where they use Dunder pits, it can easily go to 300 parts per million. So, that's like a seven, eight times more flavor, and that comes from the Dunder pit. I've done Dunder pits with around 10 percent.

There is a moment when rum, because this comes from the rum industry, becomes offensive, undrinkable. So, a few percent is a nice way to go. So, the second cycle is Dunder pit.

You basically take back set, let it rot in a controlled environment. In your case, we're not, at least, well, I thought we're not in the tropics, but it's 30 degrees here. So, maybe we should start digging a hole there as well.

Controlled environment, kefir or yogurt bacteria. After six weeks, you can play around with some additions, before you start your finishing run. So, my thinking goes like this.

I've got a lot of connections in the whiskey industry, where they use back setting. Now, I learned about this, and I changed it a bit, so it's better. Now, here's an innovation for you, whiskey guys.

Why don't you start to use Dunder pits as well? And they were a bit hesitant, and there's a reason for that, especially single malt. Whiskey is made from malted barley.

Malted grains are open, sprouted, prone to infections. You maybe don't want bacteria near that facility. But I then found out that most of them already do it.

Whiskey producers use Dunder pits, only differently. They don't dig a hole in the ground. I haven't seen one throw a rooster in, or not even kefir or yogurt bacteria.

What they do do, traditionally, for instance, is use wooden washbacks.

Common mistakes and decisions

It's called washback, which is a weird name for a fermenter, because they wash sour mash back into those fermenters before they start a new ferment. And the reason they're made out of wood is because wood is, of course, porous. It's open in structure, so you get microbiology living in there.

You ferment, but it's a controllable environment, because if it runs out of control, you just blow torch it, and you scrape the charcoal off to minimize the infection from bacteria. But by working with wooden fermenters, wooden washbacks, they actually do introduce biological microbiology into their drinks and their associated flavors. Now, the problem became for this whiskey industry, as it grew, you can't build wooden fermenters 10, 20, 30, 40, 50,000 liters.

So they needed to change, and they needed to change towards stainless steel. Stainless steel is chemically inert, basically. Microbiology cannot start living in there.

So now, how do they make sure that they get those amazing flavors over that they used to have from working with, well, not a dunder pit, but some contamination from the woods and the living microorganisms in that? So what whiskey distilleries do nowadays to make sure they get some funky, fruity, interesting flavors from this end? They basically have cleaning protocols that are substandard or suboptimal, or they are optimal from a flavor perspective, but not from a cleaning perspective.

So bigger distilleries have pipes that can be automatically cleaned with steam, with water. And you can do that after every run. You create a sanitized environment.

But if you create a sanitized environment, no bacterial infections. And after two, three runs of not cleaning it, your microbiology, your bacterial infection starts to run out of control. That's not what you want either.

So what I usually implement is a one-in-three cleaning procedure. First one, not a lot of flavors from bacteria. And then by blending these runs, they create a certain more intense flavor profile than they could do without bacterial infection.

So even in whiskey, you can see that a dunder pit, or at least the microbiology behind a dunder pit, plays a role with big alcohol and something you can play around with. How they're not very good at making whiskies because it's not sour enough. We don't need those hops in there.

Temperature control, all the things we don't need because we do want flavors in whiskey beer in order to harvest them and concentrate them. One of the reasons why, in general, a good brewer isn't very good at distilling is because brewers are all about sanitation because beer is a low-alcohol drink. And since it is a low-alcohol drink, it will spoil if there's a bacteria present.

So they clean everything meticulously. They would steam the residue out of it like two times out of one instead of one times out of three just to make sure that that beer, that batch of beer doesn't get ruined.

Continue with Connects dunder dosing to boiler-charge preparation stage. to build directly on this foundation.

Key Takeaways