Rum: Fermentation Craziness

Rum Fermentation

What defines a high quality perfume? You  would probably respond: “what defines a good perfume is the length of essence persistence on our skin”. That’s right! But what makes the perfume stay on your skin longer? Well, two factors: the essence concentration and the alcohol quality. The luxury perfumes need a very complex alcohol, full of volatile matter also called congeners. These congeners, also known as “secondary aromas” are the natural result of the biochemical process called fermentation. Those “non-alcoholic matters” are acids and oils with lots of aroma range. They cling to our skin and help other essences (in case of perfumes) to stay longer.

Now, talking about Rum, the quality and fermentation possibilities are infinite thanks to the raw material that is used: sugarcane. It is, by far, the sweetest plant on earth. But before we continue, a quick explanation about what fermentation is. When a fungus called “yeast” eats sugars in the right environment (the sugar saturation should not be more than 140 -160 gr / liter) and transforms this sugar into alcohol and CO2 through this biochemical process, we call it “Fermentation”. This is when “secondary aromas” (congeners) are born, the result of reactions during fermentation. The longer the fermentation, the greater amount of secondary aromas. The bigger the amount of secondary aromas, the heavier the Rum profile will be. This secondary aroma quantity will define the Rum profile, its aroma range and quality. Without good fermentation, there is no good Rum.

You can ferment three “states” of sugarcane: juice, syrup also called honey “A type” or molasses also called honey “B type” or “C type” (if the sugar amount is really low). A pure juice will have around 180-200 grams of sugar/ liter; sugarcane syrup will have 800 to 900 grams of sugar/ liter and molasses will be around 600 to 700 grams/ liter. Of course before fermentation starts, the producers will have to low down (dilute with water) the sugar content until the optimal concentration which is 140-160 grams/ liter, otherwise the yeast won’t be able to start properly.

Now take note that there are three fermentation systems: Spontaneous (Single-stage, natural, uncontrolled process activated by wild yeast), Discontinuous controlled (Single-stage, controlled process activated by selected yeasts) and Continuous controlled (Multiple-stage, controlled fermentation activated by selected yeasts).

To make the idea simpler, I’m separating the fermentation “timings” in four length ranges: 

  • 24 hours or less (which is an “industrial fermentation”. Very low secondary aromas quantity). 
  • 24 to 36 hours (which is a “short fermentation”. Enough in case of sugarcane juice fermentation but not enough for syrup or molasses fermentation).
  • 36 to 72 hours (being this one called “medium fermentation”. Balanced, structured, not too light and not too heavy). 
  • More than 72 hours being possible to arrive up to two weeks (called “long fermentation”).

I had the chance to see the magic process of Jamaican long fermentations and it is incredible how heavy and rich the profiles become from such a long process. The legal limit for human consumption of the most fruity secondary aroma called esters (ethyl acetate) is 1600 mg/ 100 ml. I saw with my own eyes and smelled with my nose something that one particular Jamaican distillery does, which was a “Rum” with 7000 mg/ 100ml. That is crazy! Actually, this is the heavy and incredibly aromatic alcohol that most luxury perfume brands use as their secret ingredient so the final result becomes unforgettable.

Depending on each producer’s tradition and style, the Rum profile will be determined by the chosen sugarcane “state”, the fermentation typology and the fermentation length. This process creates the bedrock profile that will determine the final result and its quality. Of course, we can’t forget about distillation and ageing, but I will write about it in the next chapter of our Rum journey.

Read Chapter 1 in this series: The Three Rum Revolutions And The Beginnings Of Rum
Read Chapter 2 in this series: Rum: The Sugarcane Journey