Arroyo’s First Report (1938)

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I finally got a hold of one of the earliest Arroyo documents. This is the Annual Report For The Fiscal Year 1938-1939 from the University of Puerto Rico Agricultural Experiment Station.


In the document we see the first reports of the birectifier and learn how far along with other ideas they were at the time.

The Birectifier in rum manufacture. The manufacture of a good rum necessitates the constant supervision of the biological and chemical process involved. The Birectifier of Dr. Curt Luckow of the Berlin Institute of Fermentology, is an invaluable apparatus for the evaluation of commercial and aging rums. This Station has imported one of these Birectifiers to make fractional distillations of rum samples which will reveal the true nature and constitution of the beverage under examination, and at the same time will indicate under expert management whether or not the rum is a genuine product. It is also of invaluable assistance in following the maturing process of aging rums. Its use has been of great help in our rum researches and we recommend it to those interested in the manufacture of rum or similar distilled spirits.

We have certainly opened up the birectifier to “similar distilled spirits” with an immense amount of case studies.

An idea of the work that is done with the help of this apparatus will be obtained by a perusal of the general conclusions arrived at after the fractional distillations of over 20 samples of genuine rums in our laboratory:

1. The greater part of the low boiling point esters and aldehydes are obtained in the first two fractions distilled, probably in azeotropic mixtures with the ethyl alcohol. These first distillates, although intensely aromatic, lack the original scent of the sample under fractionation.

2. During the distillation of the second half of the third fraction ascending temperatures of distillation are registered. This indicates that chemical compounds of higher molecular weights begin to pass over at this point, especially the higher alcohols congeneric of ethanol.

3. Still higher boiling point bodies pass over during the distillation of the 4th, 5th and 6th fractions. Some of these bodies prove to be insoluble, or only partly soluble in water, as starting with No. 5 fraction great turbidity is first noticed, and later on standing, oily drops may be seen floating on the surface of the distillate. This oily substance is what we call rum oil. It is one of the most valuable constituents of a genuine rum, especially of the Jamaica type.

4. Fractions Nos. 7 and 8 are devoid of ethyl alcohol; but very high boiling point esters and aldehydes still persist in these last two portions of the distillate. Usually the turbidity of the distillate disappears in these last two fractions.

5. The characteristic aromas of fractions Nos. 4, 5 and 6 recall better than those of any other fraction the original bouquet of the sample under fractionation. This is especially so in fraction No. 5. The highest molecular weight esters and aldehydes are also obtained during the distillation of fraction No. 5. (See figures 12 and 13.) (Rafael Arroyo, F. Marrero and L. Igaravidez.)

This is more beautiful and simple language to understand the birectifier fractions and conforms perfectly to my experience. Next up is a wild observation that was Arroyo’s most speculative idea. At this point he is not yet pronouncing the observation of mitogenic radiation, but we can note that he had seven years to think about it before publishing an update in Studies On Rum (1945). To many contemporary scientists, this would sap some of Arroyo’s credibility, but I still have not heard any plausible explanation where his observations may have been wrong or what the phenomenon observed may actually be.

Radiant energy from bacterial cells new factor in symbiotic phenomena. Work conducted in the delucidation of certain phenomena encountered during symbiotic fermentation between yeast and bacteria in rum manufacture, led to the discovery of an important factor in symbiosis among microorganisms.

It was found that the bacteria had the power of inducing a high rate of multiplication and metabolism on the yeast cells with which they grew. The enzymal activities of the yeast cells were greatly activated resulting in a more rapid destruction of the sugars with subsequent appearance of the metabolic products of yeast fermentation. In certain cases morphological changes were observed resulting in a striking swelling of the cells, giving them the appearance of the so-called giant cells; the youthful cycle of the yeast cells during fermentation being also prolonged.

The most striking observation made in these studies was the fact that this stimulus acted best and with increased vigor when the two cultures were separated from each other by a quartz wall. This increased effect through quartz is explained on the grounds that since the metabolic products (especially the butyric acid) of the bacteria are not in actual contact with the yeast cells, they cannot exert their inhibitory influences on yeast growth and propagation; and, hence, the beneficial effect, meets with no contravening factors on its action upon the yeast cells. (See figure 14.) (Rafael Arroyo.)

I really have no idea what to think about this and would love any thoughts someone may have.

The natural rum aroma. Our research work on the production of quality rums of various types led us to a study of the different factors contributing to the development of the characteristic natural aroma.

The great advantage in the development of a natural characteristic aroma in a given rum lies in the fact that once the objective is attained, the resulting bouquet of the individual rum in question will be almost impossible to imitate through artificial means. On the contrary, any artificially imported aroma will be easily found and imitated by competitors.

The aroma of a well matured, genuine rum is influenced by at least two groups of factors: (1) the aggregate of aromatic bodies originally existent in the raw distillate; (2) other aromatic bodies formed during the maturing process. Among this second group are included modifications suffered, in the shape of oxidations and condensations by some of the substances mentioned under (1).

The first group is by far the most important, as its nature will determine to a large extent the quality and quantity of those aromatic bodies formed under (2). So great is the influence of No. 1 group of factors that it may be stated that a poor raw distillate will never be transformed into a cured product of true worth and merit.

With the exception of the Rum Oil, the aromatic bodies of the first group are much better known than those of the second. This is due to the fact that many of the condensation and oxidation products formed during the maturing stage in oak barrels, are easily decomposed or degraded into simpler bodies with different aromas through the action of heat since existing analytical methods require the redistillation of the cured product previous to its analysis, only those bodies not susceptible to this decomposition or degradation will be found unaltered in the sample after passing through this distillation. Hence the analytical sample will never truly represent the rum from which it is taken.

The aggregate of aromatic bodies in group No. 1 is formed during the fermenting or the distilling stages, and is inherent to the raw distillate. A very small part may come unchanged from the raw material used for fermentation, but these are met only occasionally and in negligible amounts.

The formation of the aromatic bodies mentioned as group No. 2 are the result of a very complex process not entirely dilucidated as yet. Some are formed through modifications of some of those in group No. 1; others are the result of the influence of the chemical compounds extracted from the staves of the barrel itself, or to the interchanges of these extracted bodies with those already present in the raw rum. Catalytic agents encountered in the wood of the barrel; the oxygen of the air; the temperature and relative humidity of the surrounding atmosphere, are contributing factors in the formation of new aromatic bodies as well as in the modification of others already existing in the raw distillate.

The whole problem is very intricate and of a very complex nature. There is no question, but that further and careful study of the subject is very much needed. Analytical methods for the testing of matured rums, especially with the end in view of acquiring a better knowledge of their chemical constitution, should be revised and improved upon. (Rafael Arroyo.)

There is some familiar language in there and an acknowledgement that Arroyo knew of rum oil at the beginning of his work. In the next section they give more attention to rhum agricoles and we see the emergence of pasteurizing the juice and centrifuging it. The question is: were the French already doing this? or was this an Arroyo innovation? I suspect we will find out by translating more of Kervegant.

Rum types greatly modified through variations in fermentation technique. Creation of new types also possible. Much work was devoted during the last fiscal year in studying the modifications in the chemical composition as well as organoleptic character of rum types through the introduction of innovations or changes in either mashing or fermentation operations. The results obtained gave us the general impression that here lies a vast field of endeavor in scientific rum making. So far, the industry has contented itself with following the old accepted routine in mashing and fermentation methods, little realizing the great improvements and changes that may be achieved through systematic variations of technique.

Rums manufactured from sugar cane juice were given different treatments either during mashing or fermentation with the following results:
a. Rums resulting from the fermentation of raw fresh juice as obtained directly after milling, were faulty as to yields, bouquet and aging qualities. The time taken for acquiring maturity and mellowness was too long, and even then the quality was not of the first order.
b. Rums in which the raw cane juice was pasteurized at 80°C. for 10 minutes previous to mashing operations and final fermentation, were of much better quality than those from untreated cane juice; aged far more rapidly; and besides, the yields were from 8 to 10 percent greater.
c. Rums where the juice was defecated and clarified previous to mashing and fermentation, were of still higher quality as to taste and bouquet. Besides, their maturing properties were fully developed in a comparatively short aging period. Yields were about the same as in case (b) above.
d. Rums fermented at constant or nearly constant pH value during the entire fermenting period offered a raw product of great cleanliness of aroma; the aroma itself being of a very smooth and delicate nature. The product ages very fast and the mature rum has mellowness, smoothness and delicacy of taste.
e. Symbiotic fermentations between yeast and certain “fungi imperfecti” gave rise to a really new type of rum quite different to any of the well known types in the market. It had a decided resemblance to fruit brandy and apple jack when matured. Highest yields were obtained.

As raw cane juice rums obtain a price nearly twice as high as those from final molasses in the local market, where they are greatly used as blenders, an effort was made to obtain a molasses rum possessing the characteristics of sugar cane juice rum. Here again, we met with quite successful results, although at the expense of yield. More work is considered necessary along this line. Variations in fermentation technique were responsible for the results so far obtained. (Rafael Arroyo, F. Marrero and L. Igaravulez.)

It appears they started their investigation giving more attention to raw cane juice rums than at the end a decade later.

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