This was a fascinating exercise though the results were subtle. There were no glorious sensory revelations, but I got the information I wanted and generated a lot of insights. The birectifer also proved itself to be capable of diverse analysis. Distilleries with GCMS instruments likely cannot reapply them to this kind of task so easily.
What I analyzed here was liquid from the infamous muck hole known to be used in Jamaica style ferments. Muck is essentially yeast peptonized with a mixed culture dominated by LAB. This particular pit has developed for a few weeks, but estimates of ideal residence time may be 40 days. Right now I’m monitoring this cistern with titration and observation via microscope. I plan to add a few other measurement that I think will add a much fuller understanding of what is going on and how best to use the products.
Something surprising was that the muck had both a lot of dissolved gas which I believe LAB is capable of generating as well as a significant intact alcohol content. Being the product of the bottom of a fermentation, it starts with the same alcohol content as the ferment, but what is mildly surprising is that no bacteria in the mixed culture metabolizes the alcohol or at least not rapidly.
For birectifier analysis, I started with 115 ml of 87.5% spirit to start with 100 ml of absolute alcohol which is the basis of fraction alignment. I added 135 ml of unstirred broth from the top of the cistern. This gave me a total of 250 ml. The ethanol from the 135 ml muck portion could be as high as 10 ml of absolute alcohol and it is very important to account for it (I learned after the fact). This alcohol throws off the alignment of fractions 5-8. A future strategy would be to either start with less than 100 ml of absolute alcohol such as 95 ml or to simply create a fraction 4b and start the fifth fraction by temperature and not by volume.
At its best, this muck smells like peach and is overall pleasant relative to dunder infected with the same mixed culture. The main objective was to figure out where that peach aroma resided and what other fractions (and thus zones of volatility) were effected by the muck. The old literature claims we should find the high boiling point oils first noted by E. Bauer in the late 19th century.
Droplets of Bauer oil ended up being readily visible in fraction 6, but possibly they belong in fraction 5 and did not end up there due to the misalignment from the ethanol native to the muck. Fraction 5 was hard to evaluate, first because fusel oil bled into it from fraction 4, again due to misalignment, and second because its alcohol content was higher than it should be, bauer oil possibly dissolved in that ethanol and was not visible out of solution.
If we can successfully align fractions 5-8, visual observation of bauer oil may be a benchmark of process optimization.
Something else notable was the lack of any distinct character in fraction 1-4 and then the gustatory acidity detectable in the late fractions. Muck is apparently all about these late high boiling point acids. They no doubt can easily be quantified with titration. These acids will become eventual esters.
There are a lot of potential variables to test to make a muck hole as productive as possible. How it is fed as well as residence time are very important. Maintaining a constant pH may also be an important strategy. Some bacteria in the mixed culture could be proven to produce high value volatile acids if sugar is incrementally fed. Eventually, we’ll need to figure out if volatile acidity comes from yeast breakdown or is the product of other stuff like residual sugar. The old literature hints at things working both way, but it also looks like there is a lot of ways to be confused when you are only using crude tools.
Something else to note is that lees can be fed into the muck pit dead or alive. Alive they will have come from a drained fermenter, while dead they will be settled from dunder post distillation. This differentiation may effect residence time.
The muck broth is essentially yeast extract and can be used for nutrition in the ferment, however it will increase fusel oil and so historically was only done with fission yeasts that were abnormally low fusel oil producers.
A lot more could be said here, but I’m out of time.
Fraction 1: No distinct ethyl acetate, possible slight acetaldehyde character
Fraction 2: Very neutral
Fraction 3: Very neutral
Fraction 4: Fusel oil character but likely just from analysis ethanol which was light but not neutral.
Fraction 5: Fusel oil character seems like it has over run into this fraction because the absolute alcohol was in excess of 100 ml. Something was added here by the muck but it is a little hard to evaluate.
Fraction 6: Distinct gustatory acidity, but less than fraction 7. Otherwise this feels incredibly neutral. Droplets present on surface.
Fraction 7: Distinct gustatory acidity, almost a unique mouthfeel. This fraction was not distilled to volumetric completion, but should be next time.
Fraction 8: This fraction was not collected because the distillate smelt very neutral, but should be next time to evaluate the acidity.
The fraction 4/5 transition need to be collected by temperature because fraction alignment is most important at the end, 5/6/7. Droplet quantity will likely tell a story.
Another thought is that next time I should definitely use an extremely neutral spirit so I can evaluate the fusel oil. Some bacteria in this mixed culture are known to product butanol so that would give me a chance at detecting it. This cistern is quite small, but when it grows, I can split of volumes to test little theories.