One of the big surprises at the Lallemand Alcohol School was Vivian Wisdom’s description of using sugar cane vinegar at Hampden. I never mentioned vinegar in my own Grand Arôme presentation, but I lack the first hand experience of Wisdom or the extensive travel and surveying of others. Based on the literature, I thought the process had been made obsolete by sulfuric acid. Arroyo never mentions vinegar and I don’t recall Fahrasmane ever mentioning it either. Maybe Kervegant will?
So what is the significance here? If you put vinegar into your ferment, how do you get your spirit out without being pricked?
Vinegar for rum production was prominently on display in the last post featuring an early S.F. Ashby document and it appears in other very early 20th century works of the Experiment Station. In the early references, the focus is more on the how’s than the why’s. The how to’s are interesting and this cane vinegar was made from the infamous rum canes that were singled out for rum production because they were rat eaten or diseased by boring insects. These canes would be incredible vectors for micro organisms and whatever takes hold in the cisterns could give Kombucha a run for its money (if not basically be Kombucha). REMEMBER, do not sever the goat’s head, simply brush its teeth and throw the tooth brush into the cistern.
Reading Ashby, vinegar is/was used to create enough osmotic pressure to select for Pombe fission yeasts over Saccharomyces budding yeasts. However, that likely is not the end of the story. You’d think long chain fatty acids accumulated in dunder would be enough to select for Pombe yeasts.
Another possibility is that they want the acetic acid to react with ethanol during distillation to form ethyl acetate boosting the ester number. This is possible, but ethyl acetate is not the high value portion of the ester number and is often fully evaporated in many processes that High Ester/Grand Arôme rums are purchased for.
Tobacconists evaporate ethyl acetate leaving more extraordinary, higher boiling point, higher molecular weight compounds behind. Confectioners do the same. Perfumers likely cut it away in their exotic isolation and compounding processes. The ethyl acetate therefore is likely incidental. And, it really fucks up the experience when you try to actually drink these industrial purpose rums. I finally had the Lontan Savanna Grand Arôme from Reunion which was a bit of a train wreck for unblended beverage consumption.
If something redeeming came out of the vinegar process, how could we find it? I posited that the birectifier could be used to evaluate the quality of vinegars underneath all their acetic acid. A variation of this idea came to me years ago and was a Distiller’s Workbook exercise that got edited out for being too speculative at the time. In the exercise, apple cider vinegar was converted back to cider brandy by adding ethanol and forcing out the vinegar by a combination of chemical salting (baking soda) and separation by distillation. At the time, I did not have a good enough command of what I was doing (or why) or a tool as good as the birectifier.
200 ml Apple cider vinegar 5% acetic
105 ml 95.5% Everclear (100 ml of ethyl alcohol)
The added ethanol helps separate congeners by relative solubility in addition to boiling point.
I collected 7 of the 8 traditional birectifier fractions ignoring the last one because I ran out of time. Much could be done to improve my protocol like letting the vinegar and ethanol marry for multiple days. This should also be heated under total reflux (think sous-vide) for many hours to generate as many esters from longer chain acids as possible. If these longer chain acids are not noticed in their ester form, they may be overlooked after being trapped in the later fraction and stillage nullifying the point of the exercise (the point is to notice noble characteristics).
The fractions are interesting. The first fraction is quite concentrated with ethyl acetate. This was either present in the vinegar, partially present in the Everclear or possibly formed in the still during its time under heat. I expected detectable acetaldehyde comparable to the dry vermouth I recently examined, but did not find anything obvious. Vinegar is fully oxidized so it seems probable it would be there, but it may have been obscured at the sensory level by the ethyl acetate.
If the vinegar was re-fermented in the rum wash, yeast could reduce the acetaldehyde back to ethanol. This process was first described by James Guymon of UC Davis, but was known much earlier in folk wisdom as a way to revive spoiled wine. I have no clear idea if the yeast can do anything to the acetic acid itself.
The second fraction was proportional to the first as you’d expect and the third was quite neutral.
The fourth fraction was a little odd and could represent an error on my part. It had the character of appreciable fusel oil, but also the vibrant aroma of apples. The temperature at the very end was also in line with what should have been the very beginning of fraction 5, meaning I possibly botched something (I think I know where***). There was no detectable acetic acid so far.
Boom, fraction 5! This is the fraction where you collect the very last of the 100 ml of ethyl alcohol. It was hard to detect by olfaction any pricked vinegar aroma until you tasted it and then it was clear as day. It is hard to say what the perceptual differential between detecting acetic acid in olfaction and gustation means if anything. Do the other esters and olfactory features do anything to perceptually change the obviousness of the vinegar? By gustation, there also was no overly distracting amount of acetic acid. It was manageable.
What I conclude is that you can satisfactorily evaluate vinegar with the birectifier, pressing anything of high value into fraction 4/5 and isolating anything with off character to 6/7/8. Distillation with intense reflux pushes acetic acid so far back that you can practically examine other features of the vinegar and look for extraordinary characteristics that could prove the process in rum making is redeeming.
A next step would be to integrate alkaline lime to salt out a percentage of the acetic acid to reduce it as a sensory distraction. This may give a better glimpse to how cane vinegar contributes to production. Heavy rums styles are known for large and elaborate buffers. Alkaline substances like lime or baking soda can be added to salt out acids while sulfuric acid can be added to trade places and release acids trapped in salts such as seen in the High Ether process.
Are significant amounts of long chain acids (precursors to high value esters) produced in the vinegar? Is rum oil unlocked? The birectifier may be able to tell us without having to resort to elaborate chromatography processes.
Is the process a relic that needs to be cut away to create suave, Arroyo-esque, stand alone versions of the High Ester/Grand Arôme rums? We have the tool and frame work to find out! (And I suspect, yes.)
(*** The error that happened was the boil ground to a halt and there was strange surface tension phenomena on the top. You end up with dancing water drops that never easily reintegrate into the surface. This is really hard to believe until you see it. You are distilling along like normal … then you stop. In this situation, I had to stop distilling, disassemble the birectifier and add glass boiling stones (be careful of eruption!). I probably lost a few milliliters of ethanol in the process messing up my fraction alignment.
What I think happens is that the sample has glycerin as an additive (or the previous sample). The first time I experienced the phenomenon was with Angostura bitters, but it persisted into the next sample because the boiling flask was only rinsed with hot water and not ultrasonically cleaned. The boil would undulate, creating super heated hot spots and pressure could intermittently release into the birectifier column, blowing bubbles through the vapor trap into the inner rectifier.
In the vinegar situation, the rum sample I distilled before the vinegar likely had added glycerin (or the Everclear?). It is really odd how little it takes to have an impact. Boiling stones can prevent the boil from completely grinding to a halt, but they do not prevent an undulating boil that intermittently super heats. I think I am correct on why this happens, but it is a rare phenomenon I’ve only seen a few times and I haven’t done any more elaborate tests.)