Refining my "Apartment Rum" recipe - experimental results

[GavinLeeds]

Big fan of rum in general, and my local foodservice warehouse was having a sale on molasses, so I decided to try a few different approaches. My goal is to make a tasty (obviously) spirit with a bit of complexity to it, specifically the fruity esters and funk that makes old style rum so compelling.

However, I live in a small flat, and have only a five gallon alembic still that fits on my hob, and three 5 gallon fermenting vessels, so some creativity was necessary here in order to get all the constituent flavor components. Since many rum washes start with either a bit of backset or dunder, I decided to do a pre-ferment of two gallons, of which one gallon would replace water in the final two five-gallon ferments. An open-air ferment will introduce many yeasts and bacteria, but the stuff floating around a city apartment is probably not as desirable as that floating around an orchard, so I went to visit my parents, and helped myself to their plum tree.

Returning home, I lightly rinsed the plums (about 8 small ones in total), separated the pits, and muddled them in the bottom of a two gallon bucket. The wash recipe I'm using is one gallon of molasses to five gallons of water, so I scaled that down for a final volume of two gallons, and added it to the muddled plums along with 5 grams of "Premium series LalBrew high performance ale yeast,” which is what I had on hand. I let this ferment on the counter for a week covered in cheesecloth, added a slice of rinsed pineapple skin for extra wild yeast, and let it go another week, punching down the fruit cap as necessary.

First source of error - not using a yeast intended for the spirit I'm making. I'm not sure why I didn't just order some rum yeast, but oh well. It probably would have enhanced the flavors of this run, which were complex and pleasant but delicate to the point of being weak.

For the main ferments, I used the same 1:5 ratio, scaled for a final volume of 5 gallons, and used a gallon of the wild ferment as part of the 'water' portion for each of the batches. I pitched the same yeast, which has a pitch rate of 0.5-1.0 g/l, and in total I put about 11 grams of yeast in each ferment.

Second source of error - not pasteurizing the wild ferment before adding to main. In a lot of the rum recipes I've read, some people are pretty carefree about adding their dunder to their main ferments, relying on the brewer's yeast to outcompete the more biodiverse fraction. In my case, despite obtaining a pretty stable colony of bacteria and yeasts in the pre-ferment (which soured nicely!), the ferment was still kinda sweet after about a month, and fermentation was quite slow, which greatly reduced my final yield. It's probably my fault for tempting fate, because the ONE batch you don't take an initial gravity on is always the one that gets stuck! I'm not sure to what degree stopping the growth of that portion would affect the flavor, I think the excellent, if light, flavors of this run may be due to the continued activity of the wild yeasts and bacteria.

I did a stripping run of both 5 gallon ferments after a month of fermentation, and that's when I discovered that the sweet taste of the wash wasn't just unfermentable sugars. I think I only started getting alcohol at around 90c, and barely 55% at that. Despite this, and despite running the still hard, the flavor was excellent, very sweet and light on the tongue, with a bit of flowery fruitiness. However, I really wanted more flavor, so on the spirit run I decided to cut the low wines with some 'true dunder,' using the same 2-gallon bucket from before, but this time with only a bit of pineapple skin to encourage some wild yeasts to take over.

It was pretty well behaved after a few weeks with just a light film across the top and a smell of coffee and bread, but during the final week developed a really thick SCOBY with a more fruity aroma. However, when I peeked under the cheesecloth, I was deeply uncomfortable with having... that on my countertop. I held my breath and dumped the entire thing (final volume around one gallon) into the still, releasing an unholy cloud of spores that haunts my dreams to this day, and did a spirit run.

Third source of error - adding the 'wildlife' cap instead of just the liquid below - from what I've read since, it's not always necessary or desirable to add this portion, but in my case, the flavor was still nice.

Spirit run results:
About a liter and a half of final product, minus feints. Currently aging with a sherry-marinated oak chunk, light toast, at 45% ABV. The flavor profile is pretty nice, darker and more caramel-y than perhaps I was going for, but a bit of fruitiness, and substantial (but not unpleasant) funk. It's not great in a cocktail, but on its own is an enjoyable flavor experience.

Second Batch

Looking to increase the ABV and fruitiness, I made a second batch of two 5-gallon ferments, but this time upped the molasses from 0.82 gallons to 0.9 gallons to 4.2 gallons of water, and added a 48oz can of pineapple juice (preservative free) for a starting gravity of 1.070 and 1.068, respectively. I also added 3 teaspoons of yeast nutrient to each batch to make up for the lack of wild ferment nutrients. I thought I'd try to separate out the flavor components and inoculate a gallon of wash with 0.3 liters of live kombucha, trying to get some kind of lacto/aceto fermentation going on. Unfortunately, this didn't really work very well (I suspect it needed to be acidified more before adding the live cultures), and what grew on my countertop was just not something I wanted to look at every day, so I poured it out. It did smell kind of sour and berry-ish (ethyl lactate?), but the white cheesy film was just too gross (and wasn't a kombucha SCOBY, either). Maybe if I have a shed someday (lol home ownership, my generation is fucked).

The two all-brewer's-yeast ferments took off like rockets, fermenting down to dry in two weeks. The wash tasted quite bitter, but when backsweetened a little, the flavors were nice. I did a single-distillation spirit run of one of the ferments, with a small computer fan aimed at the onion dome to encourage a little extra reflux. Spirit started coming over at 75% ABV, and at a lower temperature than before, so I was pleased, but unfortunately, the taste left a lot to be desired. There was definitely some fruit in the headsier portions of the hearts, but the whole heart spectrum was cut through with a slight rubbery off-odor. I let the cuts sit for two days to settle, but wasn't thrilled with the flavor. More than anything it just kinda smelled like the inside of the still after a run.

Two theories present themselves here - fermenting to too high an ABV (around 10% instead of 8, per my hydrometer), or the inclusion of the yeast nutrient, which I know can add off-flavors if not all of it is consumed. I have made all-pineapple washes before with the same brand and I'm sure it's not the pineapple. I have a third ferment, which should only get to around 6 or 7% abv, made from a huge can of macerated apricots in light syrup, plus extra molasses to bring to a decent starting gravity, plus three teaspoons of yeast nutrient, so the spirit run of this batch should tell me whether it was the ABV or yeast nutrient that introduced the off flavor.

I'm split on what to do next on the flavor angle - on one hand, I could keep trying to do a separate ferment (perhaps make a gallon of tepache https://youtu.be/JNcoYLVFCKg, pasteurize that, and use as a component of the water), or just find more sources of the key precursors and add those to the still or the wash, like cultured butter for butyric and lactic acids, half a cup of apple cider vinegar for acetic, etc, or up the pineapple juice component of the wash.

I'm curious what other people do to boost the flavor once they've made a pleasant -if delicate- spirit from molasses. I also wonder to what degree a sparkly clean still affected the flavor of the first run - I did an overnight citric acid bath for the entire vapor path before the first two distillations, there was quite a bit more dark oxide for the fourth (new recipe) one.