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I have finally been able to retrieve an important paper on rum I’ve known of for years and its well worth a look. This citation was referenced in Caribbean Rum—Its Manufacture And Quality, 1987. The paper was published in Sugar y Azucar magazine in 1975. As best I can tell, professor Kampen made a career at LSU’s Audubon Sugar Institute. Kampen published widely on industrial fermentations, but may not have pursued rum further.
There is mentions of statistics on molasses quality. Recommends a pH of 5.5-6.0 measured after 1:1 dilutions with distilled water. A higher pH may indicate the presence of free bases which contaminate the final product and too low may indicate microbial contamination. Like in Studies on Rum, steam distillation of molasses is recommended as a testing procedure. Arroyo also warned of freeing bases when liming molasses.
Claims sulfuric acid used to acidify a wash may also facilitate esterification, but I do not subscribe to that idea. At the levels used, it is more theoretical than meaningful, and to my knowledge, no studies systematically explore it. Mentions that sulfuric acid in conjunction with other organic acids may be used in place of pure sulfuric acid and that good rums can be produced this way, but claims it is expensive and the organic acids slow down the rate of fermentation.
Kampen only mentions Saccharomyces rum yeasts. Compares pure culture rum yeasts to baker’s yeast which is important for the era because use of baker’s yeast was still common.
Kampen gives us a paragraph on Dunder and Skimmings.
Dunder is the bottom product of a distillation column. It is rich in both yeast nutrients and acids. Skimmings are the froth collected from the surface of the treated mixed-juice in the sugar factory; they contain ethereal oil. Both dunder and skimmings are quite often used in the production of more heavy-bodied rums, to which they impart a special character. Wild fermentations, still used in Martinique, Guadeloupe and Jamaica, quite often start with a pH value of about 5.0, achieved by adding only dunder.
I have never seen a pH value tied to dunder practices of this era. Skimmings by this time are more of a bygone concept so it is interesting to see how they are described here and you wonder what specifically the author has observed.
Kampen’s paper does not have a bibliography, but goes on to present some of Arroyo’s ideas:
Bacteria. Suitable bacteria in pure culture may be used in the production of heavy-bodied rums. Clostridium Saccharo Butyricium, especially, may yield good results, since it produces from the proteins (amino acids) in the mash a mixture of acids. Ninety percent of the mixture is normal butyric acid, while the remainder includes acetic acid, propionic acid, caproic acid and heptanic acid, which finally, may give valuable higher esters.
Saccharo Butyricum was Arroyo’s particular butyric strain. Arroyo described it as producing mostly normal butyric acid. Kampden’s additional details of the other acids allude to direct experience.
Kampen gives us some math not seen elsewhere on lactic acid bacteria infections:
They are able to produce 0.3 grams of lactic acid for ever gram of invert sugar.
A concept is then described where the degree of infection should be kept “above 10”.
The degree of infection is the ratio of yeast cell concentration over bacteria concentration.
I have not seen this metric described elsewhere. To some degree, this can be done with basic equipment but it is fairly laborious. It does raise the question of whether an amount of dunder can only be justified if whatever bacteria it brings fits within an acceptable ratio with the yeast pitched.
Kampen gives considerations for high temperature short time pasteurization and declares the “H.T.S.T.” methods “superior to all other methods used in the rum industry.”
We see a description of fermentation in the “rhumeries agricoles”:
In the first, sugar cane juice is diluted with water to a specific gravity of 1.04 to 1.05. The pH is adjusted to 5.8 with sulfuric acid. Some (NH4)2SO4 may be added, as well as minor quantities of dunder. The wild fermentation then takes place in open tanks, which are quite often made of oak wood. To start fermentation, a small portion of another fermenting batch may be added. No cooling is applied and temperatures may go as high as 110°F. The next step is a simple distillation, during which no fusel oil is removed, to about 160° proof, and then aging in oak wood barrels. The result is the “grappe blanche” rum with some 75 miligrams of esters per 100 millimeters of absolute alcohol. This type of rum is not very well appreciated outside of France.
In the second method, sugar cane juice is heated and allowed to settle. The clear juice is then decanted and concentrated in evaporators to a specific gravity of about 1.15. Large quantities of dunder are added, from 10 to 35 percent of the total volume, while water makes the balance to achieve a specific gravity of about 1.075. A wild fermentation and simple distillation, and aging in oak wood follow. These rums contain up to 160 milligrams of esters per 100 millimeters of absolute alcohol, and they possess a well-rounded-off character.
In the first description, how much sulfuric acid would they be adding if they were taking molasses and reducing the pH to 5.8 which is considered quite high? Perhaps their molasses is pH 6.2?
Kampen then presents a third more modern method of fermentation featuring pure culture yeasts and flash pasteurization of the substrate. A claim is made that fusel oil can be minimized both controlling for temperature and making sure sufficient inorganic nitrogen is present in the wash.
During the fermentation process, the ratio of fermentable sugars over ash decreases continuously. As this happens, the yeast cell find it increasingly difficult to obtain the sugars for its metabolism, while, at the same time, the increasing alcohol and mineral concentrations in the mash act as inhibitors toward the cell. For this reason, fermentation methods in which the fermentable sugar content is kept approximately constant through the logarithmic, or exponential phase are superior to other methods.
Kampen goes on to describe use of a yeast centrifuge before distillation; “since the predominantly organic compounds would otherwise decompose at the prevailing high temperatures in the beer still (220°F.) and foul the rum odor.” Notice that 220°F. is well above 212°F and implies some sort of slight pressure build up.
The paper goes on the describe continuous distillation, the generalities of aging, followed by byproducts and effluent disposal.