Open or covered fermentation, specifically for rum

[Al The Chemist]

Hey folks,

 

I’m on a mission to make a rum that doesn’t just have hints of funk and fruit, but has those flavors clear and present. I’ve managed to get a fair grasp of “synthetic acidification” for the wash, though I’m feeling like I’m missing some of the organic chaos in the process.

I’ve heard a lot of talk about open fermentation for whisky. And from the conversations here about Ph crashing in rum I can only gather some people are getting bacterial infections from open fermentation. Though I haven’t heard any open discussions on this (at least none that I could find).

I’m used to fermenting covered, sanitized and locked.

Anyone interested to talk a bit about their experiences with open fermentation for rum? Specifically for the wild organism factor.

 

Cheers!

[Kindred Spirits]

I always opt for closed fermentation, and recommend it for clients.  It just better allows for you to control the variables that are involved with the process of fermenting.

You have a super interesting thread going on the synthetic acidification, but have you also experimented with cultivated dunder? I am not talking about a pit just sitting there putrefying but rather dunder that is "fed" specific fruits to enhance the specific phenolic compounds which can be fed into your wash at time of distillation, or into ferments.

Over the years I have cultivated a number of these "sweet dunder" pits as I like to call them. They work amazing for imparting some amazing fruity characteristics to the final product.

[Bolverk]

I'm with Kindred, on this one... I'd do closed fermentation and a cultivated dunder/muck pit if you really want to delve into the bacterial world. Hell you can even inoculate the pit with the bacterial cultures you want.

The whole point of the pure acids approach is to make a more consistent product by removing the variables of live bacterial infections. 

[adamOVD]

I'd also think a closed fermentation will stay warmer, and form more esters during fermentation, if that's the goal.

My rum ferments are certainly slower, with fewer nutrients than a grain fermentation, so I'm even more concerned with sanitization. The only PH problems I've actually had are from all sugar washes during the dark days of hand sanitizer, and a PH buffer solved that.

Kinda off topic, but one note that I've discovered on closed fermentation, if you pick that route, is the need to open it up for a day or so before distilling, or agitate it vigorously to release the desolved CO2 in the wash. It's not so nice coming concentrated out of the parrot.

[Al The Chemist]

Thanks for the info everyone. I’ll keep my fermentations closed. If you’re open to share, I’d love to hear more about the “flavored dunder”. The backset I store is essentially sterile, do you rely on natural bacteria and yeast for the fruit itself to kick up the process?

@adamOVD the CO2 tip is interesting, I haven’t considered that. I’ll definitely give degassing a go before fermenting.

As for heating. I have heat elements operated by an inkbird to keep the wash at the ideal temperature for the yeast. My rum fermentations tend to go pretty strong. I pushed the SG on this latest one a bit high, though so far so good.  

[Kindred Spirits]

2 hours ago, Al The Chemist said:

If you’re open to share, I’d love to hear more about the “flavored dunder”. The backset I store is essentially sterile, do you rely on natural bacteria and yeast for the fruit itself to kick up the process?

Yup you got it, I use the backset from the runs, its full of dead yeast and other nutrients leftover from the distilling process and then pretty much just smash up the desired fruits without washing them, to add some fresh wild yeasts, or inoculate it with some fresh yeast.

It all depends on what profile the client is going for.

[Al The Chemist]

Got it, so you get a full “pelicose" layer forming on that dunder?

Considering fruit don’t really carry their more traditional flavors over fermentation and distillation, did you find any that help the more banana, butter scotch, caramel, vanilla, side of things? I figured Bananas would be an obvious one, but wondering if there is something more interesting and adventurous there.

I’m personally trying to aim for something rich and heavy, less light fruity. With hopefully a touch  of light acid on the pallet (along the lines of pine apple) to balance things out a bit. Hope I'm not beign overly specific here

[Kindred Spirits]

Yes you typically get a full pelicose layer, usually I like to see a thin one. The main goal is to dissolve the fruits into the liquid without getting overwhelmed with a bacterial infection.

You are correct in saying that the input from the fruits don't necessarily impart their specific flavor, but for instance apples have a multitude of phenolic compounds which can be imparted. Bananas, mangoes, pineapple, pears, peaches, have all been used.

I enjoy the experience of seeing how each one imparts different "notes" to the final product. That particular profile sounds like guava might play a nice role. Never hurts to try.

[Al The Chemist]

Understood, thank you! 

[Bolverk]

If your pelicule starts to sink your pH is low, add some oyster shells (or equivalent)

[Al The Chemist]

Great tip. I had no idea. 

[Silk City Distillers]

Are you guys disclosing fruit to the TTB?  How are you labeling this?  Flavored Rum?

[Kindred Spirits]

TTB has never given clients any issues, there are rums throughout the Caribbean that use dunder and muck pits in addition to the traditional rum washes.

The amount used, percentage-wise, is so miniscule in the grand scheme of things they don't seem to care.  It is based upon 90+% of rum backset so even if you used a bunch and the dunder made up 5% of the total ferment/pot charge, the dissolved fruit would only be .5% at most of the overall wash/distillation.

Its like adding another ingredient like oyster shells for pH control or nutrient for yeast health. A small enough addition that doesn't change the classification of the spirit.

[FIVE x 5 Consulting]

I'm with Silk City. Setting aside the fact that it's a normal production process all over the world, here in the US it is technically not Rum if you have fermentables other than cane products - doesn't matter the quantity. If fruit and/or sugar derived from fruit makes it into your ferment, you're in distilled spirits specialty territory.

Yeast, enzymes and treatments like oyster shells are not fermentables and are not material to this analysis.

I'd sure hate to put a ton of effort into a product like this only to find out later that you cannot call it Rum on your label!

[Kindred Spirits]

Technically the fruit is not fermenting, its just dissolving into the substrate. Even if it does ferment It's a few pieces of fruit in hundreds of gallons of dunder, which equates to a few thin slices of fruit in a fermenter.

That's like saying a single malt isn't a single malt if its got a few kernels of corn in it. Or a bourbon isn't a bourbon if you use the same paddle to stir a bourbon mash and a rum wash. 

Ground coffee has an allowable amount of rat feces and cockroaches in it, it still is classified as coffee. The TTB has been around for a while now and they know not everything is 100% absolute.