The Aroma OF Rum IV, 1940 (Influence Of The Pre-Distillation Treatment Of The Fermented Material)

Arroyo R. El Aroma Del Ron IV (Influencia del Tratamiento Pre-Destilatorio del Material Fermentado). Revista Agricultura Industria Commercio Puerto Rico, Vol. 32 (1940), No. 3, pp. 416-417.

[This may actually be the Aroma Del Ron V and been printed as a typo in the original journal.]

The Aroma Of Rum
IV
(Influence Of The Pre-Distillation Treatment Of The Fermented Material)
By RAFAEL ARROYO, Ch. E. & S. E.,
Especialista en Fermentaciones Industriales; Jefe, División de Química Industrial de la Estación
Experimental de la Universidad de Puerto Rico.

Once the process of alcoholic fermentation is finished, the distiller, conscientious of the final aroma of their product is still presented the opportunity to condition or modify, and always improve it.

There are two courses to follow with the fermented batición, the first consisting (very usual in practice) in proceeding immediately to its distillation. In this case nothing else can be done as far as modification of the aroma is concerned that was not during the distillation itself. The second course to be taken consists in a special treatment to which the fermented material is subjected before proceeding to its distillation. In this second case, which is what motivates this article, we can do a lot in terms of modifying and cleaning the aroma. Among the practices to follow, there are three of more importance:

(1) Elimination of all solid matter in suspension in the fermented liquid, including the yeast itself

(2) Give a more or less long lapse of time to the fermented beating, with subsequent elimination of all solid matter.

(3) Inoculation of the fermented batición with certain microorganisms selected in advance to infuse a desirable note into the aromatic range of distillate, with subsequent removal of solid matter in suspension.

The first of these practices must be carried out in all cases because of its transcendental importance not only in the cleaning of the aroma, but also for many other economic reasons that come into play later during the distillation and aging of the product.

For the reader to better appreciate and understand the effect of the aroma of rum on the removal of the suspended solid matter found in the fermented liquid, it is necessary to state the nature of this material and the effects it produces during distillation in the formation of that repulsive odor which we call “tufo”.

During the fermentation period we can notice the separation of certain components of the raw material in solid form, most of which clump together and agglomerate as sediment in the bottom of the fermenter together with a large amount of yeast. Another part, that is more dispersed, remains in suspension in the liquid with many yeast cells, or residues resulting from the autolysis of the same. Most of these bodies in suspension are nitrogen products such as yeast gum; pectic substances; albumin, and yeast cells. When these nitrogen organic bodies pass with the liquid of the batición to the still during the distillation stage, they originate a large part of the “tufo” in the distillate; because they are broken down by the heat and reducing atmosphere in the column. If the distillation is carried out carelessly, then the decomposition of these bodies increases greatly, and the “tufo” of the distillate is consequently much greater. Therefore, by eliminating these nitrogenous substances from the batición we are automatically eliminating one of the pungent and frequent malefactors of the aroma.

When the distiller has taken the necessary precautions to ensure a fine and delicate aroma in its fermented material, it only needs to protect it from contamination during the distillation, eliminating these “tufo” producing bodies before passing it to the still, which is why we have indicated that this first practice must be applied in all cases.

When a pleasant aroma has not been created during the period of fermentation in the necessary degree, or intensity; or it has been obtained partially and incompletely, then the distiller can implement the resting process in combination with the removal of solid matter. A resting period of 24 to 48 hours will be given to the fermented batición under favorable conditions; that is, in a specially constructed tank for that purpose. This tank should be able to be sterilized before receiving the fermented batter and should keep it free of contamination during the time it occupies.

During this period of time at rest the aroma of the distillate can be greatly improved, since it offers an opportunity for the termination of chemical reactions between the products of the yeast metabolism, which need some time for the formation of aromatic substances that they should greatly favor the bouquet of the distillate. We could say that the aroma softens, reaching the desired aroma set.

In the case where the distiller has not succeeded in forming the aroma set during the fermentative period, and it deems necessary to develop the salient characteristic of the bouquet of the distillate by means of other microorganisms that impart that special bouquet, it can thus achieve that once the alcoholic fermentation is finished, by inoculating the fermented batición with a pure culture of the fermentative agent in question. Once finished the new fermentation induced by the latter, you can then proceed to the removal of solid matter in suspension as in the other cases already mentioned.

The choice of the second fermentative agent imparting special aroma is a matter of great importance and careful technique. Three conditions are essential here to operate successfully in this way:

1. The organism in question must be able to ferment the residual sugars of the batición in the presence of the products existing there generated during the previous alcoholic fermentation. In other words, the products of yeast metabolism should not serve as inhibitory agents to the fermentative activities of the second ferment.

2. This second ferment must produce metabolic products that in themselves enhance the aroma of the distillate; or that, otherwise, can be combined chemically with the products generated during the alcoholic fermentation, with the subsequent formation of valuable bodies in the synthesis of fine bouquet.

3. The time taken for this secondary fermentation should not be excessively long. Neither should this secondary fermentation result in the decomposition of the products already formed by the yeast; especially ethyl alcohol.

Now, these pre-distillatory or post-fermentative practices (as you want to call them), although of great value in the development of a fine bouquet, and cleaning of “tufo” require additional equipment and operating facilities rarely found in the existing distilleries in the country.

It seems to us, however, that nothing would be lost, and that our distillers could earn a lot, establishing small experimental plants within their commercial distilleries to dedicate them to this kind of research work. The lack of a research department in any industry is a sure omen of stagnation, and even near extinction.

In matters of manufacturing quality rum, studies are most needed; everything is to be learned. The field is open to exploration and study is, in our concept, unlimited. We have long years of study and experimentation dedicated to the manufacture of genuine rum, and we firmly believe that we have barely begun to glimpse the immense possibilities within this industry.

3 thoughts on “The Aroma OF Rum IV, 1940 (Influence Of The Pre-Distillation Treatment Of The Fermented Material)

  1. Thanks for the article! Your articles and collection of papers is fantastic by the way.
    My question is about this second fermentation stage mentioned. Can you direct me to and other information on the topic? Is it just addition of another type of yeast in a starter perhaps?

    Thanks again

    Byron

  2. Hi Byron, Arroyo covers the specifics of fermentation complications (what I call secondary fermentations) best in Studies on Rum and my scanning is floating around the web (I never hosted it on the blog). There are a lot of potential complications–from alt-yeasts that matabolize proteins forming esters to classic bacterias like the butyricums. I’m not that far in my trials. Right now I’m only working on Pombe yeasts and learning to run them through a “pentathlon” to find a champion rum yeast. I expect to find some more of Arroyo’s papers where he gives us more specifics. Somewhere in Kervegant’s text you will also find more ideas.

    Cheers! -Stephen

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