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. This topic was covered in Studies on Rum and I was not aware of a separate article. These short articles often have more details that fill in small missing pieces of the Arroyo puzzle.
This paper is interesting because it has idea that bridge Arroyo’s career from a pioneer of ABE fermentation to rum. I would have thought Arroyo brought this idea from ABE to rum, but it appears to have gone in the other direction. We also see it reinforced that Arroyo was an expert on butyric ferments and that is part of why he was uniquely qualified to tackle heavy rum.
An interesting thing to note is the absence of lime in this description which implies that lime treatment is unique to developing aroma for rum.
The Principle of Thick Mashing in Industrial Fermentation
Procedure developed for rum industry found applicable to other industrial fermentations with molasses
By Rafael Arroyo, Ch.E.,S.E.
A principle first applied by the writer in commercial scale to alcoholic and rum fermentations, may prove of equal value in other industrial fermentations, as for instance, the butanol-acetone and the butyric acid industries. In a previous article (1) data were offered showing results obtained at a commercial distillery through the use of the Arroyo process (2) which is based on two principles: (a) the preparation of a purified, sterilized, and conditioned thick mash, previous to actual fermentation of the molasses; and (b) the incremental feeding of this thick mash to the fermenters during the fermentative lapse. The success encountered in rum and alcoholic fermentation led the writer to try the principle of thick mashing in other industrial fermentations. The butanol-acetone and the butyric acid fermentations were selected for the purpose, since the writer (3-4) had done previous extensive research in both these types of fermentations.
(1) Arroyo, R. Ethanol Fermentation of Molasses; Sugar, Vol. 38, No. 2; February, 1943.
(2) U.S. Patent No. 2,295,150
(3-4) Arroyo, R. The Utilization of Waste Molasses in the Production of: (1) Acetone and Butanol; (2) Normal Butyric Acid. The Journal of Agriculture of the University of Puerto Rico; Vol. XVII, No. 4; December, 1943.
Arroyo, R. Butyric Acid by Fermentation. The Journal of Agriculture of the University of Puerto Rico, Vol. XX, No. 2; July, 1936.
The experiments conducted, using this principle, in the butanol-acetone and butyric acid fermentations in laboratory scale have shown promising results as to yields, fermentation efficiencies, ease of manipulation, time taken for completion of fermentation, etc. They have also shown that if ever the modified technique attains industrial use on a commercial scale the following advantages will be attainable: (a) The fuel bill for sterilization purposes will be reduced to about 20% of its present value. (b) The temperature range for sterilization will be much lower than at present, pressures above the atmospheric being entirely eliminated, except for the preparation of seed for the fermenters. This means ease and security of operation plus further saving of thermal units. (c) There will be enormous saving of cooling water during mashing operations. In fact, practically no cooling water will become necessary for bringing the thin mash to inoculating temperatures, since the water of dilution used to convert the thick mash into thin mash will also act as cooling agent. (5) The purification undergone by the molasses during thick mashing results in better and more rapid fermentations due to the removal of non-sugars from the molasses. (e) There results a great economy of plant equipment, especially in heat exchangers, cookers, boilers, pumping machinery, motors, pipe lines, etc. (f) The sterilization of the thick mash being conducted under high acidic conditions, the sterilization temperature may be relatively low, which means less loss of sugars through caramelization, and more efficient fermentations. (g) The withdrawal of mineral and organic impurities during thick mashing helps to keep the stills free from sealing and fouling for longer periods between shut downs for cleaning purposes.
The present practice in butanol-acetone and butyric acid plants of diluting blackstrap molasses from about 88° to 8.8° to 9.5° Brix, and then subjecting this very thin mash to bulk sterilization at high temperatures, with the necessary subsequent cooling to inoculating temperatures, means that enormous amounts of thermal units must be applied for sterilization purposes, and then taken away through water cooling of the hot thin mash in heat exchangers or otherwise. Thus great amounts of fuel must be burned for the production of steam, and enormous amounts of cooling water must be pumped for the cooling of the mashes. This is a particular disadvantage for the successful installation of these industrial fermentation processes in the tropics, where the raw material is both abundant and cheap.
With the end in view of ameliorating these conditions of high fuel price and scarcity of industrial water, the procedure described below was finally adopted in our experimental work with both the butylic and the butyric fermentations. The mash used for the preparation of bacterial seed for the fermenter was thoroughly sterilized under pressure as customary in standard practice, but the preparation of the main fermenter mash was carried out quite differently. Blackstrap molasses of about 88° Brix was diluted with ordinary tap water from the city mains to a density between 60° and 62° Brix. This thick mash was acidulated through the addition of strong sulphuric acid in such amounts that the pH value was lowered by 0.5 units. The thick mash was then heated to between 90° and 95° Centigrade, and kept at this temperature range for at least half an hour. While still hot, it was supercentrifuged for separation of precipitated impurities of both inorganic and organic nature. The clean effluent was then further diluted with tap water at room temperature (about 27° C.) until a Brix reading between 8.8 and 9.4 was obtained. The pH of this thin mash was adjusted with strong ammonia water to a reading between 5.7 and 6.0, and the mash was inoculated immediately with a 10% footing of a vigorous, actively fermenting bacterial culture. The results obtained with this modified mashing procedure were in every respect comparable with those obtained in the usual process of bulk sterilization of the thin butyl or butyric mash, as will be seen from a perusal of tables I and II respectively. Table I offers results under standard methods of mashing and sterilizing, while table II offers results obtained with our modified mashing and sterilizing practice.
