Jamaican Rum on Acid: How Vinegar Brings the Funk

The learning never stops.

For several years I’ve endeavored to understand the flavor science and history behind Jamaican rum’s unique hogo. As part of that I’ve visited every Jamaican rum distillery, save one, and documented what I learned. One such article I wrote was perhaps the first to clearly define what dunder is, and differentiate it from muck, a related but very different ingredient.

To briefly recap, both dunder (what remains in a still after a distillation run, aka stillage), and muck (a putrefied dunder with other ingredients added) are substantial parts of the fermented wash of the next distillation run. You might call them the “special sauces” of Jamaican rum making. I refer to them frequently when educating people about why Jamaican rum is often so flavorful.

Note: Not all Jamaican rums use dunder or muck. It’s only the strongly flavorful ones that do.

I recently realized yet another special sauce is in use; one right in front of my eyes for quite some time. I’d failed to connect my understanding of historical texts with what I personally saw in Jamaica. It all came down to a simple labeling issue.

This third special sauce is vinegar – a special distillery crafted vinegar made from cane juice. You might be wondering why on earth you’d add vinegar to molasses for your fermentation. The answer: To make more flavor! But probably not the flavor you’re picturing.

Not what the Jamaican rum makes use

Vinegar is a diluted form of acetic acid. This common acid, when combined with ethyl alcohol, creates the ester known as ethyl acetate. Ethyl acetate is by far the most common ester found in rum, making an aroma typically described as fruity. Others say it bring to mind nail polish remover.

During fermentation, yeast consumes sugar and emits ethyl alcohol. By adding acetic acid to the mix, the distiller creates more opportunities for the alcohol to combine with the acid, birthing an ethyl acetate ester molecule. Simply put, it supercharges flavor creation!

Let’s wonk out just a bit deeper on this.

Charles Allan, in his magnificent 1906 lectures for the Jamaican Sugar Experiment Station, writes:[i]

Acetic acid is the acid of vinegar. The method in which vinegar is made is interesting as, in some measure, the same process is followed in making acid on estates making flavoured rum. The wine which is to be converted into vinegar is placed in casks, half filled, at about 30 degrees C. to which air has moderately free access. The formation of acetic acid takes place in consequence of the liquid being gradually covered with a film consisting of the mother of vinegar. In other countries the German quick “vinegar process” is employed in which the growth of bacteria suspended in dilute spirit mixed with vinegar, is accelerated by coming into intimate contact with the air. This is brought about by allowing free access of air, by dividing the liquid into small drops and distributing these over a large surface (such as beech shavings.)

Acetic acid must be produced in large quantities in the distilleries of this island but especially in those making flavoured rum. Indeed in them special processes have been evolved to produce this acid as well as others. The part of the process which is mostly concerned in the pro duction of acetic acid is the fermentation of what is called rum cane juice. This juice is generally poor in sugar and what sugar there is, is mostly glucose which would not crystallise out even the juice. It is however, in a suitable state for being fermented. A weak alcoholic solution is formed. This liquor is thrown over cane trash and allowed to stand. The result is that the alcohol is turned into acetic acid. You will note how closely this process corresponds to that of making vine gar. Only in the case of vinegar-making a freer access to air is given.

Note: Flavoured rum in this context doesn’t mean anything like Bacardi’s Dragon Berry rum. Rather, it refers to the high ester rum exported to Germany to make rum verschnitt, and to Amsterdam for blending and flavoring purposes.

So, now we know more about how the Jamaicans were making vinegar a century ago. The next question is: How much vinegar were they using each time? A cup? A gallon?

More than you might think. This same document referenced earlier provides a recipe for a typical wash to make a highly flavored rum:

Capacity of fermenting cistern 2,000 gallons.

  • Skimmings (fresh) 620 gallons at 12 brix
  • Dunder 760 gallons at 24 brix
  • Acid 220 gallons at 8 brix
  • Molasses 200 gallons
  • Flavour 160 gallons at 8 brix (aka “muck”)

The acid in the recipe is cane vinegar.[ii]

In this particular example, several hundred gallons, about 11 percent of the wash.

Cane acid (vinegar) tank at Long Pond distillery, Jamaica

Unfortunately, I’d not yet read the above excerpts prior to visiting Long Pond. When I saw a tank labeled “acid” in the fermentation area, I blithely assumed it was for waste, or maybe for a cleaning solution.

In a nutshell, I took a long time connecting the dots between the acid referenced in the 1906 text, and the acid tank I saw in Long Pond’s fermentation area. Instead, I (erroneously) assumed that the use of vinegar was an old practice that had fallen out of favor.

It wasn’t until I hosted an online session with National Rums of Jamaica that it clicked – The “acid” tank I’d seen at Long Pond was in fact a cane vinegar tank, clear evidence that acid is still used by some of today’s Jamaican distilleries. It’s not a forgotten practice after all! From the session, we also know it’s used at the Clarendon distillery as well as at Long Pond.

In short, when talking about the special practices that make Jamaican rum so ester-rific, don’t forget cane vinegar!


[i] Allan, Charles; LECTURES ON FERMENTATION IN RELATION TO JAMAICA RUM.  As delivered at the Course for Distillers —AT THE— Government Laboratory in 1906.

[ii] I find it rather starting to contemplate this old wash recipe. Only ten percent of the recipe is molasses, a far cry from most rum making today which is usually entirely from molasses. In those early recipes, dunder, skimmings and vinegar makes up more of the recipe than molasses.