Arroyo R. The Aroma of Rum : VI. Influence of the Distillation. Revista agricultura industria commercio; Puerto Rico, Vol. 32 (1940), 593-594.
The Aroma Of Rum
(Influence of the distillation)
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.
It is not enough to have developed a distinguished and exclusive aroma during the stages of rum manufacture prior to the distillation of the product. It is necessary to know how to preserve (and improve if possible) that aroma during the distillation period. Actually this is the easiest stage to carry out in terms of aroma quality; provided that the precautions already described in the previous articles have been observed. But otherwise, that is, when the necessary measures and care have not been taken, we can affirm that during this distillation stage the formation of the desired bouquet will suffer great changes and setbacks.
Having already stated in previous articles how most of the “tufo” is formed during the distillation in those cases where the necessary fermentative and post-fermentative precautions have been lacking, we will make concrete in this short article exposing the measures to be taken during the distillation of the product to conserve, purify, or modify the natural aroma already formed in the fermented material in those cases only where we have already done everything possible in the maintenance and improvement of the aroma until the time of distillation.
The idea of how to carry out the distillation is, of course, associated with the distillation apparatus to be used. If, in relation to other rum manufacturing factors, the selection of the distillation apparatus is sometimes extremely difficult without first making a complete analysis of the inherent and peculiar conditions in each case, the same is not true when the only factor in the balance is that regarding aroma quality. The choice is simple and definitive in this case: In order to obtain the best results in terms of natural aroma quality in the raw distillate, we have to carry out the distillation in an intermittent distillation system. And we do not say this festively, but as the result of our experiments and observations.
In the course of our investigations in this regard, we have had the opportunity to compare rums and brandies in whose elaborations the only different factor consisted in the method by which they were distilled in each case; and we have always found great aromatic superiority in those rums and brandies that were distilled in discontinuous distillation stills.
Where does this great aromatic superiority come from distilled rums in intermittent-type stills? The causes are several; but in a short article of this nature we will only limit ourselves to exposing the three most important ones:
1. Stills of continuous distillation lack the means to obtain the degree of fractionation necessary for the separation of the aromatic bodies in their various degrees of goodness within a given class. From which it turns out that bodies of relative aromatic inferiority pass mixed with the superior and most desirable ones, to the distillate or raw rum. In trying to eliminate these lower aroma bodies, we find that, in order to do so, it is necessary to sacrifice a large part of those that we desire in the distillate and that we had tried with care and attention to develop and perfect during the stages of rum manufacture preceding distillation.
2. Another powerful cause is the greater flexibility of operation of the discontinuous system. Using this distillation system we can select almost at our whim the aromatic range of the crude distillate; that is, we can select from the set of aromatic substances existing in the fermented material both in intensity and quality those that we most desire, and separate the others. And this is not possible when using the continuous distillation system.
3. We have spoken several times in the course of this series of articles, of one of the most valuable elements in the composition of the natural aroma of a genuine rum. This valuable component, called rum oil is an essential oil of chemical composition unknown until the present. Well, when we carry out the distillation by means of a continuous distillation still, 90 percent of this valuable component does not appear in the raw rum, but is lost in the musts (slops) of the still. The reason for this loss is due to the high boiling point of this substance, which does not find sufficient heat in the column of the still to follow the course of the other condensable vapors towards the final condenser. When we use an intermittent distillation apparatus this valuable essential oil has the opportunity to appear at least partially in the raw rum, it passes in an adequate quantity when the distillation temperature begins to rise due to the thinning of the ethyl alcohol concentration in the ascending vapors towards the condenser.
There are still other advantages in favor of the distillation of the product in alambics of intermittent distillation; but the three mentioned above are the most conspicuous.
When we use an intermittent distillation still we can select at our whim the degree of aromatic intensity that we wish to impart to the distillate. Everything depends on the greater or lesser time spent in the total reflux of the condensed vapors before starting the actual distillation; and of an intelligent division of the distillate between the respective products commonly known as “heads”, “bodies” and “tails”.
We end this article recommending intermittent distillation as most appropriate for the conservation and improvement of the aroma developed during the successive stages in the manufacture of pure and genuine rum; as it is the only way to produce better and more pleasant aroma. Economy issues of time, space and fuel are discarded in this dissertation, which concerns solely and exclusively the quality of the aroma in the crude distillate.