Arroyo 1941: The “Tufo” (stink) of Crude Rum

EL Tufo del Ron Crudo
(Its Elimination Without Resorting to Chemical Oxidants or Substances)

Por RAFAEL ARROYO, CH.E. & S.E.,
Especialista en Fermeniaciones Industriales; Jefe, Division de Quimica Industrial de la Estacion Experimental Agricola de la Universidad de Puerto Rico.

When we began our studies on rum manufacturing, one of the problems that interested us the most was the elimination of the so-called “tufo” or bad smell that the raw distillates tend to incur very often within current practices. We noticed at once that maintaining other constant conditions, and following the technique known until then, the crude distillate offered more “tufo” in inverse ratio to the proof degree to which its distillation was carried out; that is, the lower the degree of distillation the higher the “tufo”. This explained to us the almost general practice among our distillers of maintaining grades that fluctuate between 170° and 189° in the distillation of their products.

The fear of the rectifiers towards the rum with tufo soon degenerated into such a mania, that one confused with “tufo” any smell of the distillate that was not that of ethyl alcohol. The rapid preparation of “rum” by the incorporation of odor, color and taste to the crude distillate emphasized much more the custom of the distillation at high proof levels, and until the rectification of the distillates in intermittent stills, previously obtained to the highest possible degree proof in the continuous distillation stills. The producers, of course, wanted alcohol, and they did not rum, since the aroma and taste were going to be imparted by means of the so-called “sauces” or “bases”, for the manufacture of quick rum.

But when distilling at these high proofs and using processes of rectification in the production of crude rum, although it is true that the “tufo” is significantly reduced, it is no less true that the system or practice leads to other complications of great importance; for example:

1. These distillation practices eliminate some of the congeners of the ethyl fermentation that give more value to a genuine rum of quality. Among these, aldehydes and esters of high molecular weight with high boiling point, and very especially the constituent that exerts greater influence on the stability and aromatic persistence of rum. The adaptability of rum to be used in punches, cocktails and other diluted beverages depends largely on these components.

2. No matter how high the proof of the crude rum during its distillation, it becomes necessary to dilute it, since it is essential to reduce the high alcohol content to the usual concentration of the market, that is, between 85 and 90 degrees proof. At any stage of the process in which it is carried out, this dilution will be detrimental to the rum; and this damage will be greater when more quantity of diluent is used.

3. The kind of diluent, the way to apply it, and the most opportune moment to carry out this operation constitute a problem in the manufacture of rum.

4. Some of the problems with the dilution of rum have a great influence on the marketability and general acceptance of the product. For example, sedimentation in the bottle containing the rum is a direct consequence many times of the kind of diluent used. Sometimes the diluent contains water soluble impurities that are less soluble in mixtures of water and the constituents of rum. Other times, “sauces” of taste and aroma are used, some of whose components react with those of the diluent to produce precipitations that appear in the form of sedimentation in the bottom of the bottle.

Imbalances of the taste and original bouquet of rum, alterations of the body, separation of certain aromatic principles that cause opalescence in the liquid, and other minor ailments are often originated from the processes following the dilution of the crude rum.

Taking all this into consideration, the search for a “modus operandi” by which we could distill at low proofs, for example between 130° – 110°, seemed to be natural and pertinent to obviate the use of diluent as much as possible; and that at the same time to obtain a low proof distillate free of “tufo”.

To cure the disease, it became necessary to know its causes. Therefore, we dedicated a large part of our time to the determination of the main causes of the “tufo” in a crude distillate. To abbreviate this article, we will not cite in detail the experiments carried out with this object, but we will concretely state that the results of our investigations showed us that the so-called “tufo” comes mainly from two causes:

1. That part of the “tufo” already brought by the raw material, or formed during the fermentation process.

2. That part of the “tufo” formed during the period of the distillation.

The first, although of less intensity and volume, is nevertheless the most difficult to correct once formed. The method employed to correct or avoid the formation of the second, although very efficient in this respect, is completely ineffective for the elimination of the tufo cataloged in cause No. 1.

The best way to avoid the formation of tufo during the fermentation process has been thoroughly detailed in past and recent articles, by which we only mention that first cause, without going into details and explanations.

Regarding the second cause, because it is a stage of our work carried out very recently, we had not had occasion to make it known to our readers. The elimination of this second part of the “tufo” is done by purely mechanical action and is therefore easy to install and practice in any distillery.

We found in the course of our experiments that the increase in the “tufo” of the raw distillate depended directly on the content of solids in suspension in the fermented liquid at the moment of its entrance to the distillation process. The greater the degree of heat in the distillation, the greater the accentuation of the “tufo” in the distillate. The cells of the yeast, and other substances of organic origin and highly nitrogenous, constitute one of the most objectionable solid matters in relation to the “tufo”. Apparently the cooking of these nitrogenous products in the still, and the temperature at which it is made, bring with it decompositions responsible for the bad odors that pass to the distillate to form the cause No. 2 of the “tufo”. At the same time, poorly skilled handling of the alembic (especially those of continuous distillation) would increase this result due to overheating of these nitrogenous materials on the walls and plates of the column.

At first we could only partially separate these solids in suspension, either using the natural decantation of these particles during a more or less long period of rest, or by filtering batición en masse with inadequate filters, that although they separated the comparatively large particles, let pass those of microscopic size; among these the yeast cells. In all cases we could observe that the greater the cleaning of solids in suspension, the better distillates we obtained in terms of flavor and aroma of the product.

Thanks to the interest and cooperation of our Director, Dr. Nolla, we had the opportunity to push our tests to the limit, acquiring the services of a yeast separating centrifuge, De Laval brand. We have been experimenting with this centrifuge for a few months, and we can say without fear of error that the results obtained so far fully meet all our requirements and even our demands. Below we will give the results obtained with this device in the separation of solids and elimination of “tufo” working with cane juice baticións:

In our practice, as soon as the fermentation ends, we centrifuge the batición en masse. During the centrifugation the fermented batición is constantly stirred to obtain a suspension of solid matter of almost constant concentration. This facilitates the work of the centrifuge. The filtrate obtained is quite transparent and is completely free of solid matter in suspension of a size greater than that of a high colloidal dispersion. Microscopic counts of yeast in the batición before and after treatment indicate 99.9 to 100.0 percent cell separation. This liquid is subjected to distillation immediately or after 24 hours of rest. Below are the advantages obtained:

1. During the centrifugation of the fermented material, many dissolved gases that would interfere in the rhythmic unfolding of the distillation in the still are removed from the liquid; and some of which would pass dissolved in the crude distillate contributing to the so-called “tufo”.

2. We can, if we want, recover all the yeast formed during the fermentation period, thus ensuring a valuable by-product.

3. The alembic, which previously had to be cleaned often, is now kept clean almost indefinitely. We have not cleaned it again since we used the centrifuge for the first time.

4. The musts (slops) lack the characteristic bad smell that disgusts those who live near a distillery.

5. The problem of the dilution of the crude oil to reduce its alcoholic content has been solved, because we have distilled as low as 95 degrees proof satisfactorily as far as the presence of “tufo” is concerned.

6. Our objectives in this regard have been realized.

Disadvantages obtained? There is only one, which is however solvable with a more efficient setup than ours. I mean that with our centrifugation equipment there is the disadvantage of a small loss of alcohol during the centrifugation of the fermented batición. This is because the equipment is open to the atmosphere; but we believe that by doing this operation under cover, the alcoholic loss would be greatly reduced or become null.

The results expressed above have been obtained under our methods of fermenting and distilling, which differ somewhat in some respects, and much in others, from those prevailing among our distillers. We believe, however, that the De Laval yeast separating centrifuge would be useful in any distillery no matter what methods prevail in fermentation and distillation. The advantages listed above will surely be easy to understand for our distillers; whereas the only disadvantage is, as we said before, easy to correct.