Follow along: IG @birectifier
I helped a scientist across the world find a missing paper by Rafael Arroyo and this led to a few more I did not have from the journal Sugar, 1945. These short articles have details that fill in missing pieces of the Arroyo puzzle.
This document is a unique variation of Arroyo’s US Patent, 2,386,924,: Production of heavy rums. Some people have waded into this, but no one has truly danced with it. No such rums exists on the market. There is so much to it and you can’t really cut corners. Nearly 80 years later, few are even capable of the analysis work that Arroyo performed in the 1940’s. There is molasses prep, then growing your own yeast, then your own bacteria, then you must perform really challenging measurements to find a window for ideal activity by your bacteria who is easily inhibited. Then you are distilling a way that no one currently practices!
Something that facilitated Arroyo’s ideas was experience with the birectifier. It taught lessons related to what congeners were where that influenced his unique take on distillation. It also taught him what to target. He possibly even used fractions to create model distillates to pursue, and that can be seen where he has opinions on congener ratios that don’t really appear in the literature elsewhere. It is not a stretch to say the birectifier turbo charged his understanding of distillation.
It is interesting to speculate on what Arroyo drew from to put this all together. He was already an ABE fermentation wizard and that is where the large skill set with butyric acid bacteria came in. Where did he first hear about fission yeasts? How did he know to treat molasses with lime to facilitate the production of rum oil? Did he read the Jamaican works of Percival Greg or did chatter still float about from old timers? Producers had ideas on quality they never put to use because everything was always “uneconomical”.
Can you follow it all? Do you see the unique connections to the rum literature or Arroyo’s experience with the birectifier?
How much would it all cost today and what modern advances make it relatively easier to execute? Cory Widmayer and I have played with this for years, but we have found it becomes a full time job and takes real resources. Centrifuge or not, you can’t do it as a hobby. I’m confident we could execute it with real resources. Too bad all the money piled onto a whiskey glut…
The Production of Heavy Bodied Rum
A procedure which shortens the time of fermentation and aging and gives high yields and fermentation efficiencies
By Rafael Arroyo, Ch.E., S.E.
The so-called heavy rums have usually been differentiated from the more common and better known light rums, by their non-alcohol number and by physical and organoleptic differences of body, taste, and aroma. The heavy rums are the ones preferred in continental Europe, while the light rums are preferred in the United States. With the termination of the war there will be great opportunities for the United State Caribbean possessions to enter into the European rum market, but before the opportunity can be utilized it will become necessary to be able to manufacture heavy rums of the highest quality, conforming to the standards that are required by European importers.
A heavy rum possesses a higher non-alcohol number and a richer and more intense taste and aroma than a light rum. It is also distinguished by a very high index of persistence in both aroma and taste, by which is meant that it can endure high diluting with aqueous solutions of neutral spirits before its characteristic aroma and taste can no longer be perceived by an experienced taster. While the heavy type of rum has been manufactured in the past, and is being produced at present, most of the methods hitherto followed have been of a haphazard or empirical nature, and therefore coupled with uncertainty in execution, with results that frequently have been detrimental to the quality of the finished product and to the economy of the process, or to both. These facts have been evidence in practice by the much greater consumption of light rums, especially in America. Two main reasons exist for this: (1) the few wholesome, genuine heavy rums on the market are too expensive for the average purchaser; (2) most of the low priced heavy rums on the market are improperly fermented and distilled, or are artificially concocted. For instance, it has been sought to manufacture heavy rums by merely changing the method of distillation as used in the manufacture of light rums, so that more of the so-called head products are allowed to pass over into the main distillate or raw commercial rum. This was thought to increase the non-alcohol number and to add the necessary extra flavor and aroma. These attempts, however, have failed to produce a first class, genuine heavy rum, since what is really accomplished by such procedure is the addition to the main distillate of undesirable congenerics of the alcoholic fermentation, being in fact the same products that are so carefully and painstakingly eliminated when manufacturing the light type of rum. Obviously, a carelessly distilled light rum is not a first class, genuine heavy rum.
It has been found that the presence of certain bacteria in the fermenting alcoholic medium aids in securing flavor and aroma for the resulting rum, and a second prior practice has been to carry the rum fermentation forward in a substrate which was purposely badly infected, and in which all kinds of unidentified bacteria and other microorganisms have competed with the rum yeast strain in the fermentation of the sugars present in the mash. The success or failure of such a method of heavy rum making depends on the kind and extent of the infection present. Even when successful as to the quality of the product, when by chance or luck the right kind of bacteria, and only such, are present as the infecting organisms, this unscientific practice leads to poor results with regard to yields and fermentation efficiencies.
It has been found however, that heavy rums of excellent type and with high yields and fermentation efficiencies can be obtained by a procedure comprising: (1) the subjection of the raw material to a pretreating operation which fits it for its intended use; (2) the selection of yeast and bacterial cultures adapted for symbiotic fermentation of heavy rums; (3) the employment of optimum conditions for the production of alcohol and of the right kind of aroma and flavor; obtaining at the same time rapid fermentation, a high quality product, and high yields and fermentation efficiencies; (4) the employment of a proper and rational distillation method for the resulting beers, founded on the principle of selective rum distillation.
As an illustration of the process, the procedure may start with employment of a blackstrap sugar cane molasses. This blackstrap is pretreated to improve it chemically, physically, and biologically. For this purpose, a cylindrical iron tank is equipped with a thermometer, steam coils, and a motor-driven mechanical stirrer. It is preferred also to connect it to the still condenser outlet, so that hot water from the condenser may be supplied into this pretreatment tank, to afford saving of heat units during the pre-treatment operations. The molasses is brought into the pretreating tank and mixed with a predetermined amount of milk of lime which is calculated to raise the pH value of the molasses by 0.5 pH; the actual amount to be employed for treating the introduced weight of molasses is determined experimentally according to the density and original pH of the raw material, and the amount treated per batch. After introducing the milk of lime, the stirrer is set in motion and hot water from the still condenser is added, with vigorous stirring, until the resulting mixture attains a density that may vary in practice between 55° and 65° Brix, preferably 60° for normal Puerto Rican molasses. The hot water is then shut off and the temperature of the mixture adjusted by introducing steam into the coils, so that a temperature between 70° and 80° Centigrade is attained; this temperature is then maintained in the resulting thick mash from 15 minutes to one hour, depending upon the purity of the molasses, the equipment available, and the schedule of operation. The molasses mixture, or thick mash, must remain below pH 7.0; that is, it is less acid but not definitely alkaline during this pre-treatment.
While still strongly agitated the mixture is next passed through a separating device, such as a centrifuge of special construction, or preferably, a self-cleaning super-centrifuge, for the separation of solid organic and inorganic impurities which have been precipitated or separated during the alkaline and heat treatment described. The clean run-off, in the form of a thick mash, is then delivered into a second pretreatment tank which is equipped like the first one, except that this time the coils are connected for water cooling. As soon as the coils are covered by the inflowing thick mash, cold water is introduced through them, and the agitation of the mass is continued during the entire cooling period. When the temperature has dropped to about 45° to 40° Centigrade, enough strong sulphuric acid is added to the tank contents to obtain a new pH value between 5.0 and 5.2. Then there is added enough strong ammonia water of 26% to 29% strength so that a final pH of 5.4 to 5.6 is obtained in the contents of the tank. Finally there is added 0.5% of ammonium sulphate, and 0.1% of calcium superphosphate on the weight of the molasses mashed. The reason for this accurate adjustment of the pH is that it has been found that the optimum for symbiotic working of the yeast and bacteria lies at around pH 5.5 for the production of heavy rums; and it is preferred to observe this throughout, both for simplicity of control and for avoiding shock to the organism when they are brought together. The mash is then passed through a second filter or super-centrifuge for the separation of new precipitated solid impurities obtained during the acidification of the mash. The cleaned, purified, and conditioned thick mash thus resulting is delivered to a receiving and storage tank, from which it is drawn as needed for mashing operations.
This pre-treatment has eliminated large portions of impurities such as molasses gums, ash, infective organism, and mechanical impurities, by the combined effects of temperature conditions and relative alkalinities in the several stages, and an inversion of saccharose has been initiated by reason of the final acid treatment. The yeast strain used should be of a type adapted to the fermentation of heavy rums. All yeast strains are not suitable for this purpose, and not even all varieties of rum yeast will serve. The best of these yeasts are to be found among the shizo-saccharomyces or fission yeasts, but a few strains of budding yeasts may also be employed with success. A characteristic of a proper heavy rum yeast in accordance with the present process is that is should be able to stand moderate, but appreciable concentrations of organic acids during the alcoholic fermentation, particularly saturated aliphatic fatty acids such as acetic, propionic, butyric, and others higher up in the series. It should be a fair to good producer of rum oil. The yeast should also cooperate symbiotically with the bacteria used as an auxiliary co-ferment.
The yeast strain is prepared to form a footing for the seeding of the fermenters by starting propagation every day at the distillery laboratory from an agar slant containing a pure culture of the yeast. By known methods of bacteriological technique, a portion of this pure culture is transferred to a biological test tube containing 25 ml. of sterile molasses mash. When this first transfer has reached vigorous fermentation, a new transfer is made into a 500 ml. Erlenmayer flask containing about 350 ml. of sterile mash, and such transfers are made in success as vigorous fermentations occur, until a seed culture of about five gallons has been built up in the laboratory. This culture is then employed as the inoculum of the first vessel of the plant yeasting equipment. A cooperative bacterial ferment is also developed in the laboratory for introduction into the fermenters in due time. It is preferred to employ Clostridium saccharo butyricum (Arroyo) as set out further on. The stock culture of these bacteria may be kept in spore form in sterile soil or sterile “bagacillo”, and is activated into its vegetative form prior to its use for building the required seed. The laboratory seed is developed in essentially the same fashion described for the yeast seed.
The fermentation of the thick mash is illustratively accomplished in a batch procedure by causing the thick mash to flow from the receiving tank into a machine for the preparation of thin mash. Here the thick mash is diluted by additional water to the required density. It is important that the density of the thin mash be kept at such a value that the total sugar concentration per 100 ml. shall not exceed 13.0 grams. The thin mashing control is determined by grams of total sugars per 100 ml. of mash rather than by the Brix density. It is desirable and convenient to maintain the sugar concentration as near as possible to the limit above given, but a lower concentration than 13.0 grams per 100 ml. mash may be employed, if desirable, with a particular molasses, yeast, or bacterium. The maximum initial total sugar concentration of 13.0 grams per 100 ml. has been selected to the benefit of the bacteria, as most bacteria of the propionic and butyric groups do not tolerate the sugars at much above 6 grams per 100 ml. mash, and are also inhibited by alcoholic concentrations of 8 percent by volume, or above. Since 13.0 grams per 100 ml. does not yield over 8 percent by volume of alcohol during fermentation (most probably about 7.0 to 7.5 percent) a safety factor is provided, regardless of the yeast action. And since the total sugars are reduced to about 6.0 grams per 100 ml. at bacterial seeding, the consequent alcohol concentration will not exceed 4 to 5 percent by volume, and the bacteria are then able to proceed with their own work in symbiosis.
The fermenter first receives an active, vigorous yeast footing before the thin mash is introduced. This footing should amount to between 5.0 and 15.0 percent, and preferably is about 10.0 percent of the total working volume of the fermenter; as this insures a rapid start of the fermentation without involving the complications inherent to the preparation of a very large footing, especially if the fermenter is of large capacity. The fermenters may be of the closed type, constructed of polished iron, or steel, and provided with mash cooling devices and means of agitating the mash, either mechanically or by the admission of carbon dioxide gas at the bottom. This carbon dioxide may be obtained from another actively going fermenter, or from compressed carbon dioxide containers. Agitation by means of air is not recommended on account of the detrimental effect of the oxygen upon the anaerobic bacteria. It is recommended also that the fermenter be provided with continuous recorders for temperature and pH. The thin mash is added upon the yeast footing in the fermenter, with a gentle stirring or agitation of the contents, so as to provide thorough and even distribution of the seed yeast. When all of the mash has been added, the pH value is noted, and contents are corrected to a value of 5.5 by the addition of either sulphuric acid or milk of lime, as the case may require. The setting temperature should be between 28° and 31° C.
Fermentation is allowed to proceed under temperature control within a range of 30° to 33° Centrigrade, preferably by means of cooling coils placed outside of the fermenters through which the mash may be circulated whenever temperature correction becomes necessary. After the sixth hour of actual fermentation, tests are made for amount of total sugars present in grams per 100 ml. of mash. Likewise, determinations of alcoholic concentrations in percentage by volume are thereafter effected every two hours. When the percentage of alcohol by volume is about 3.5 to 4.5 and the total sugars per 100 ml. of mash have a value of 6.0 grams or less, the conditions are ready for the incorporation of the bacterial footing into the fermenting mash. The fermenting mash is first corrected to a pH value between 5.4 and 5.6, if necessary. The pH value of the bacterial footing is similarly adjusted to essentially the same pH figure, and then, while gently stirring or agitating, the bacterial footing is added to the fermenter in an amount equivalent to 1.0 to 4.0 percent of the total volume of the fermenting liquid. It is preferred to employ 2.0 percent of the bacterial footing when a yeast footing of 10.0 percent has been used under the above conditions, as the ratio 1:5 appears to give an optimum result. The higher the ratio of bacteria to yeast, up to 1:5, the heavier and more aromatic is the resulting rum, but when the ratio is much higher than 1:5 there is danger of obtaining uneconomically low yields of rum, since the faster propagation of the bacteria will overcome the yeast, limiting or stopping its zymogenic powers.
After the addition of the bacterial inoculum, greater care becomes necessary about temperature control, as it is then important that the temperature within the fermenter should not go much about 30° C. Correspondingly, the pH value should be so controlled that it will never be below 5.0, as at pH values of 4.0 and below the bacterium will lose its activity and go into the spore form. The fermentation is then allowed to proceed to a finish. In case higher alcoholic concentrations than may be expected from the initial amount of sugars concentration in the mash are desired, more sugars may be introduced into the fermenter when the total concentration in the fermenter has dropped to a value between 1.5 and 2.0 grams per 100 ml. mash. This is accomplished by introducing the desired amount of the thick mash into the fermenter, with gentle agitation or stirring of its contents. The quantity of thick mash introduced is determined by the amount required to produce the extra amount of alcohol desired; and care must be observed to insure that an increase of alcohol over 8.0 percent by volume is not provoked until the desired bacterial action has occurred. When using the culture of Clostridium saccharo butyricum (Arroyo) which has been isolated and developed in the practice of this process, it has been found that the rate of alcoholic fermentation is greatly accelerated after its incorporation in the fermenter, due to symbiotic action and mitogenetic radiation effects from bacteria to yeast. The fermentation will usually come to an end in from 28 to 36 hours, counting from the time of yeast innoculation. The alcoholic yields based on the total sugars used have been found to vary between 44.0 and 46.0 percent, with corresponding fermentation efficiencies of 0 to 95 percent, based on Pasteur’s equation for the alcoholic fermentation of sugars. When no extra sugars are added, the usual alcoholic concentrations in the beers run from 7.0 to 7.5 percent by volume; while if additional thick mash has been introduced, the alcoholic concentration may be raised to from 9.0 to 11.0 percent.
In preparing heavy rums, distillation of the beers or fermented mashes is best conducted in a discontinuous or batch still provided with an efficient rectifying column and total reflux condenser. Continuous stills may be used if specially designed for the purpose. However, preference is given to the discontinuous system of distillation. In distilling, the resulting beer from the fermenter may be distilled directly, or it may be allowed a certain period of rest, varying from 12 to 18 hours. The latter practice is preferred, as it greatly improves the quality of the resulting rum. In either case, the kettle of the batch still is charged, and its contents are carefully brought to gentle ebullition. This gentle boiling should be maintained during the whole distillation period, by careful control of the steam admitted to the coils of the kettle. At the beginning of the evaporation, the ascending alcoholic vapors are totally refluxed back to the column, for a time which is determined largely by the particular characteristics which it is desired to impart to the end product. It has been found that two to four hours of refluxing increases the esterification leading to the production of high-boiling point, high-molecular weight esters which are so essential a part of a true heavy rum; besides, it causes the accumulation of low-boiling products at the top of the column, so that when the so-called head products are separated they will pass off with a minimum total volume of distillate. When the period of total refluxing is over, the distillation proper begins.
At the beginning of the selective distillation, the head products should be taken off for an amount which is determined experimentally for each individual case, and based on practice and experience. Generally speaking, and for orientation of the inexperienced in the practice, from 0.5 to 1.0 percent of the total volume of the beer should be separated as head products. After these head products are collected, distillation of the body, or main products, is continued, in a separate container. When the proof of the distillate falls to an apparent degree of about 130, the distillate is again led into the head products receiver until a new apparent proof of about 80 degrees is registered at the test gauge. At this point, the distillate is again led into the main products receiving tank until the end of the distillation period. The body of main products, composed of the second and fourth fractions, will average from 150 to 165 proof, depending on the original concentration of alcohol in the beer, the total time of refluxing before starting the distillation proper, and the rate of distillation during the operation. Those portions of distillate which have been collected in the head products receiver, being the first and third fractions, may amount to about 10 to 15 percent of the total alcoholic liquors distilled. They may be stored in special receivers until enough has been accumulated to permit a separate further distillation. When so collected, they are first diluted to an alcoholic concentration of about 20 percent by volume, and the foregoing distillation procedure is again effected thereon, with the exception that in this case the products separated from the body or main products, i.e. the first and third fractions are totally discarded.
The described process of fermentation and distillation affords a fine product, due to the presence therein of valuable aromatic bodies, and the exclusion therefrom of deleterious aromatic bodies that heretofore have been eliminated by lengthy aging. This gives a minimum expense for maturing in the case of the rums produced by the process, and, in fact, the raw rums so manufactured have been found to reach full maturity in but a fraction of the time usually allotted for the aging of heavy bodied rums. In the foregoing description reference has been made to the employment of the symbiotically active co-ferment in the form of bacteria which assist in providing the extra desired and necessary flavor and aroma constituents. A number of bacteria and a mould of the “fungi imperfecti” group were found adequate and well suited for the purpose, particularly bacteria members of the propionic and butyric acid groups. The bacteria must conform to the following specifications: (a) Their life activities should not be arrested too soon by the metabolic products of the yeast formed during the fermentation period, particularly by the ethyl alcohol. (b) They must not attack or decompose, or materially change, the existing products of the yeast metabolism to such an extent as significantly to reduce the yield of alcohol. (c) They should possess the power to act upon the residual sugars of the alcoholic fermentation, utilizing these sugars in the elaboration of the products of their own metabolism. (d) Their metabolic products should be of such character as of themselves to enhance the flavor and aroma of the resulting rum; or of such nature that they will readily combine chemically with the metabolic products of the yeast (particularly with ethyl alcohol) to form highly flavored aromatic compounds. (e) They must be of such nature as will readily and fully act in the same class of substrate as is required for the alcoholic production when the fermentation is properly conducted.
Clostridium saccharo butyricum (Arroyo) produces a mixture of valuable aliphatic acids, consisting principally of normal butyric, acetic, and propionic acids, but also including about one percent of other organic acids of higher molecular weights, such as caproic, heptoic, and others. No appreciable amounts of alcohols, aldehydes, or ketones are found in the metabolic products of this particular culture. This organism possesses also the power of irradiating the so-called mitogenetic rays of Gurwitsch, which greatly activate the yeast culture when acting symbiotically therewith in molasses mashes under the aforesaid controlled conditions. The effect of this activation appears in an increase in the power of yeast multiplication, resulting in a more rapid fermentation and formation of alcohol than when the yeast acted alone in pure culture in similar mashes. This effect is revealed in the accelerated rate of fermentation following the addition of the bacterial culture to the fermenter. It is found that the bacteria became inhibited whenever the sugars concentration of the medium was higher than about 6.0 grams of total sugars per 100 ml. of mash, or whenever the alcoholic concentration in the fermenting liquid was over 8.0 percent by volume, or whenever the pH value of the medium decreased until it approached the value of 4.0. Therefore, the foregoing procedure includes the necessary steps for maintaining the pH well about 4.0 for withholding inoculation with the bacterial culture until the sugars in the fermenter reduce to below about 6.0 grams per 100 ml. of mash, and for using such sugars concentration in the mashing operation that not over about 8.0 percent of alcohol by volume is present in the beer during the course of bacterial fermentation.
Studies of the heavy rums prepared by this procedure have revealed that preponderance in the amount of non-alcohol number was not the most significant difference between heavy and light rums. Fractional distillation on both types of rums, supplemented by chemical and organoleptic tests performed on the individual fractions in each case, have show that the most striking difference consisted not so much in the size as in the individual composition of their respective non-alcohol numbers. For instance, it was found that the individual esters and aldehydes in the non-alcohol number of light rums consisted almost entirely of compounds of low-molecular weight and low-boiling point; while in the case of heavy rums, the esters and aldehydes present consist to an very considerable proportion of compounds of high-molecular weight, high-boiling point, which pass over with the fifth and sixth fractions during fractional distillation of the sample. It was also found that the fusel oil content was higher in the case of the light rums, when considered in proportion to their non-alcohol number. The volatile and total acidities are much higher in heavy than in light rums. In actual comparative analyses of a heavy rum and of a light rum, the following differences were noted:
The ratios above indicated can be employed in estimates of rum quality in that the quality is improved, for instance, in the case of heavy rums in proportion as the ratio of high-boiling-point ester and aldehydes to low-boiling-point esters and aldehydes approaches unity. This ratio is much lower in the case of light rums. A high quality heavy rum should have this ratio always surpassing 1:2, and for the better products of the present procedure this ratio approaches and in some cases exceeds 1:1. Organoleptic tests for aroma and taste have proved that the taste and aroma of the high-molecular weight, high-boiling point esters and aldehydes are much superior to those of the low-boiling point, low-molecular weight esters and aldehydes. The “index of persistence” is from 10 to 20 times higher in the heavy than in the light rums. These indications explain why good heavy rums can not be produced by merely letting a large amount of head products pass over with the main distillate, since these products are composed almost entirely of the esters and aldehydes of low-molecular weight, low-boiling point, and poor index of persistence. It also explains why the incorporation of a co-ferment such as Clostridium sacccharo butyricum (Arroyo) or other proper organism to the fermentation under controlled biological and chemical conditions can result in great improvement of rum quality in aroma and flavor, since the acids produced by this bacterium form esters with the usual alcohols found in yeast fermentation, which are considered among the most valuable constituents of a genuine heavy rum, particularly the butyric, heptoic, and caproic acid esters.
The above conditions are preferred, but obviously are not rigid conditions for all operations. When other sugars and alcoholic concentrations in the mash are selected as more convenient or desirable, care should be taken to provide that the sugars concentration must be at or below 6.0 grams per 100 ml. of mash, and the alcoholic concentration in the fermenting mash not over 8.0 percent alcohol by volume for operation in the presence of Clostridium sacccharo butyricum (Arroyo). In fact, the bacterial culture may be added during the finishing stage of the alcoholic fermentation if desired, since the bacterium is able to utilize the residual sugars of the normal alcoholic fermentation in the elaboration of its own metabolic products; and this is feasible provided that the alcoholic concentration by volume is then at or below 8.0 percent. When additional sugars in the form of thick mash are to be added during the finishing stages of fermentation it is customary to effect the bacterial inoculation as early as possible during the primary alcoholic fermentation, since by so doing the beneficial effects of the symbiotic fermentation have already taken place before the alcoholic concentration is increased due to the newly incorporated sugars, so much as to inhibit further bacterial action.
The pre-treatment of molasses is valuable in the preparation of such beverage rum, as the molasses is thereby cleaned of foul-smelling substances, such as gases and other volatile compound usually in solution therein; and is also rid of organic and inorganic impurities which are always present in the molasses, such as excess ash and molasses gums. The successive separations, firstly upon the heat and alkaline treatment, and secondly upon the sulphuric acid treatment, lead to a far-reaching improvement of the raw material. The use of a super-centrifuge was found the most expeditious way of separating the impurities, but other means may be adopted, such as simple centrifuging in a specially built machine, filtration in a suitable filter, settling and decantation. The action of the heat during the pre-treatment renders the material practically free of microbiological contaminants, such as wild yeast, molds, and bacteria of various kind which are always present in the raw material. The total sugars concentration in the molasses is also increased through the withdrawal of non-sugars; and the action of the heat, and later the action of the sulphuric acid, serve through inversion to increase the amount of readily fermentable monoses. There is also physical improvement of the raw material in that the viscosity is greatly reduced, and the material is much more easy to handle.
The addition of the milk of lime during the initial stage of the pre-treatment process has three main purposes: (a) It prepares the medium for the development during fermentation of the most important ingredient in the aroma of heavy rums, being the essential oil, or mixture of essential oils, to which the name rum oil has been given. (b) It neutralizes the free fatty acids which are always present in molasses, thus eliminating the danger of their volatilization during the heating operation which immediately follows; but permitting the reliberation of these fatty acids from their calcium salts upon the sulphuric acid addition to the already cooled thick mash in the second stage of the pre-treatment. In this was these acids become available for the formation of valuable esters later during the fermentation period. (c) The disturbance produced in the medium through the alteration in pH values occasioned by the milk of lime causes a copious precipitation of organic bases, molasses gums, and mineral ash constituents of the molasses, and this precipitation is enhanced by the action of the heat applied. The nutrient requirements of the yeast and symbiotic bacteria are corrected at this stage when deficiencies are found upon analysis of the raw material. The aforesaid amounts of ammonium sulphate and calcium superphosphate are not restrictive or fixed, but are given as averages that have been found necessary when mashing Puerto Rican molasses. For other cases, preliminary analysis of the raw material and experimental observation will determine the amounts of the nutrients to use.
The unusually short period of fermentation is due to various reasons, such as the favorable changes in the substrate, resulting from the pre-treatment operation, the stimulating action of the bacteria upon the yeast on account of the mitogenetic irradiation, and the strict chemical and biological control exercised during mashing and fermentation. The temperature range for the fermentation previous to the incorporation of the bacterial culture may be maintained between 30° and 33° Centigrade, as this range will insure optimum conditions for the yeast strains used in this type of fermentation. At the time of inoculation with the bacterial culture, however, the temperature must be controllers within a range of 28° to 30° Centrigrade in order to keep the bacterial culture from propogating too rapidly, as it would naturally do at a higher temperature, with possible detriment to the yeast propagation and metabolic processes. It has been found in our experiments that when the propagation of the bacterial culture comes such that the bacteria is present in large quantities and surpasses the concentration of yeast cells, then its activating action becomes detrimental to the yeast, and deleterious influences are noted in the yeast propagation and metabolism.
It has been noted as preferable to employ a batch or discontinuous still for distilling the rum. Comparative chemical, physical, and organoleptic tests have indicated this preference, as it normally provides the advantages of a higher content of rum oil, which is an aromatic compound of a true oily nature which passes over during the analytic fractionation of rums in the fifth and sixth fractions; and in the distillation of the rum begins to distill over when the proof of the distillate is about 80 (40 percent ethyl alcohol by volume). It possesses the characteristic aroma of aged rums. A chemical study of this valuable rum ingredient indicates that it does not belong to the aldehyde, ester, or higher alcohol groups. Nor does it belong in the ketonic class. Physically, it is a higher refractive, colorless, oily substance, or mixture of oily substances, of unknown chemical composition, but apparently belonging to the terpenes. Its boiling point is somewhat higher than that of ethyl alcohol, and it is more soluble in alcohol than in water. The index of persistence of its aroma was found to be extremely high. Additional advantages of the batch method are that a higher body is obtained in the rum; a higher content of aromatic esters and aldehydes of the high-molecular weight, high-boiling point class is obtained in the non-alcohol number of the rum; the rum as a better flavor and aroma; the rum is higher in its index of persistence of aroma and flavor. Chemical studies of the distillation on the pilot plant batch still demonstrated that valuable aromatic and flavor giving constituents begin to pass over when the proof of the distillate approaches around 80 degrees, and also the valuable rum oil begins to distill profusely at this stage of the distillation. Hence, it is preferable to provide for reception of this fraction of the distillate in the main body receiver. The separation of a great part of the head products and of the distillate fraction which passes over between 130 and 80 proof is preferred, as this greatly improves the commercial product or main body.
The combined procedures have the advantages of a comparatively short time for the completion of the fermentation; unusually high yields and fermentation efficiencies for this type of rum fermentation; economy of floor space and labor, with low capital investment; elimination of danger of fermentation failures; maintenance of uniformity and high quality standards in the finished product; ability of the product to improve quickly with age for this type of rum; economy in shut-down periods for cleaning, as the purification of the raw materials renders the necessity of securing infrequent, and effects savings in chemicals, labor, and steam for the purpose.
You must be logged in to post a comment.