Arroyo R. El Aceite de Fúsel en los Rones. Revista de agricultura de Puerto Rico, Volume 33 (1941), 422-424
Fusel Oil In Rums
Por 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.
Fusel oil is the name used to designate the mixture of higher alcohols that generally constitute a high percentage of the Non-alcohol Coefficient of a rum. This oil consists mainly of amyl alcohol and small proportions of other higher alcohols.
Besides the nauseating smell and taste that this oil imparts to rums when it is found in very high amounts, many have been thinking for a long time that fusel oil also exerts a destructive action on health. Recent studies, however, have shown that this destructive action on the human organism is not superior to that produced by ethyl alcohol itself, and that the latter being the main component of the rums, the poor results attributed to fusel oil probably come from ethyl alcohol.
Whatever may be the question of the physiological effect of fusel oil on the human organism, the truth is that the tendency exists in the present to eliminate as much as possible this oil from commercial rums.
There are two procedures to prevent commercial rum from being heavily loaded in this oil; the first of which consists in the partial or total elimination of this product during the distillation; and the other that tends to avoid, or prevent, the immoderate formation of this fusel oil during the fermentation period.
As regards the manufacture of rum, we believe that the second of these two methods is the most effective, since when we use the first one we expose ourselves to eliminate along with fusel oil other important bodies of great need in commercial rum, such as “Rum Oil” and the most valuable esters. This work will therefore deal with the techniques of the second method.
As we have already indicated, this method is more preventive than curative: that is, it eliminates the fusel oil partially preventing its formation during the fermentation period. In this way, the distiller does not worry about the problem of removing the oil during the distillation of their rums, while not having to fear losses of other valuable aromatic products needed in their distillate.
Having recommended the second method of eliminating Fusel Oil, let us now see how this procedure should be put into practice:
First of all it is necessary to attend to three capital points, which are:
1. Selection of a yeast naturally poor in producing Fusel Oil.
2. Maintain low fermentation temperatures.
3. Provide the yeast with ample nitrogen feed in the form of ammonium salts such as tartrate, citrate or sulfate; or still much better, using the ammonia hydrate directly.
We will now give some experimental data on which the recommendation above is based:
During the course of our research on rum manufacturing, we observed a great variation in the production of Fusel Oil by different yeasts. In order to obtain specific data on this important observation we made a series of baticións for rum in the same way, and always using the same raw material. These baticións were inoculated with pure cultures of different strains of yeast respectively and fermented under conditions such that the only variant in each case consisted of the different yeast strain.
After the fermentation period in each case, we proceeded to the distillation and analysis of each of the rums. In Table No. 1, the reader will find the amount in milligrams of fusel oil produced per 100 milliliters of absolute alcohol in rum. Also the total production of the Non Alcoholic Coefficient in milligrams per 100 milliliters of absolute alcohol in rum, and percentage of this Coefficient that constitutes the Fusel Oil.
[This table also appears in Studies On Rum page 19
We also know that yeast No. 501 is a Pombe yeast which he paired with a butyricum.
Yeast No. 764, likely a Saccharomyces, was used with Suavelons]
Applying to the practice of the rum distillery the results obtained in the experiment that we have just pointed out, we would find that yeasts Nos. 501, 503 and 504, stand out as naturally poor producers of Fusel Oil and would probably be selected for the production of rums with low content of that oil. The problem would be solved only with a judicious selection of yeast provided that the selected strain fulfills other important requirements, such as alcohol yield produced; aroma and taste of rum; time necessary to finish the fermentation, etc., etc.
Effect of Relatively Low Temperatures During Fermentation
In the experiment described above, we fermented at the average temperature of the commercial distilleries, that is, within the 33-35° Centigrade range. In this second experiment we took care to control the fermentation temperature between 25-27° C and we selected those yeasts that had proved to be high producers of Fusel Oil according to the results of our first experiment. Table No. 2 contains the results obtained.
The data offered in Table No. II show us that if we ferment at a relatively low temperature, that is, between 25 and 27° C., instead of between 33 and 35° C., we can reduce the production of Fusel Oil in percentages that vary between 40.0 and 60.0 percent of those values obtained when using fermentation temperatures between 33 and 35° C.
Although without a special refrigeration system it is very difficult in Puerto Rico to maintain fermentation temperatures of 25 to 27° C, the author of these lines has seen cases of commercial fermenters whose temperature has been maintained between 28 and 29° C using water extracted from a deep well as a coolant. The initial temperature of the water used as coolant varied between 25 and 26° C.
Effect of Supplementing Yeast with Ammonium Hydroxide
We have carried out experiments to test the effect of supplementing the yeast with ammonia hydroxide using different fermentation temperatures. Table No. III offers the results obtained in this case. The same yeasts used in the experiment were used whose results appear in Table No. II.
The data offered in Table No. III show that it is achievable to greatly reduce the content of Fusel Oil in the fermented batición even when we have to use moderately high fermentation temperatures, provided that we supplement the yeast with ammonia hydroxide during the complete duration that fermentation lasts. We can also see from these data that a combination of supplemental ammonia and relatively low fermentation temperatures will give us the optimum result in terms of reducing the formation of Fusel Oil in rums as much as possible.
Incidentally, by putting these methods into practice, the distiller will get less contamination in their baticións, higher alcohol yields, better quality rum, and a product that will mature quickly in barrels.