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Parfait A., Sabin G., 1975. Les fermentations traditionnelles de mélasse et de jus de canne aux Antilles françaises. Industries alimentaires et Agricoles 92, 27–34.
Traditional Fermentations of Molasses and Cane Juice in the French Antilles
by A. PARFAIT et G. SABIN
institut National de la Recherche Agronomlque
Station de Technologie des Produits Végétaux – Petit-Bourg – GUADELOUPE
SUMMARY [their English]
A review is given here of studies which are in progress on rum fermentations in French Antilles. The influence of pH, yeast strain and sugar and nitrogen compounds concentrations are discussed.
This article reviews the ongoing studies of rum fermentation at French Antilles. The influence of pH, yeast strain and concentrations of sugar and nitrogen compounds is discussed.
The fermentations of molasses and cane juice lead to wines which after distillation give rums. From 1900 to 1945, they were the subject of many observations which Kervegant (1946) summarized. Subsequently, there has been a lot of concern about rum analysis; but the results found have not always been related to the circumstances of manufacture. Under these circumstances, it was difficult to arrange or methodically modify fermentation techniques, either to improve the quality of finished products or to develop new types of rums.
1. FERMENTATION IN THE MANUFACTURE OF RHUMS
Fermentation is a stage in the production of rums from different raw materials. Figure 1 shows the main processes. In addition, when making rum “grand arôme” and in case we want to reduce the consumption of water, vinasse can enter the composition of musts. Tables 1, 2 and 3 provide a number of data on fermentations and rums.
Some data on fermentations in the French West Indies
Analysis of different samples of rum. For the agricultural rum, the figures represent the average of 30 examples, for the rum of molasse: 6 examples. The dosing methods used correspond to those of the official French method
1.1. RAW MATERIALS
The characteristics of the raw materials have variable values. They depend on the variety, the state of maturity of the cane and the conditions of harvesting and extraction of sugar. The average composition of the cane is as follows: water: 70%, ligneous material: 14%, sucrose: 14%, impurities: 2%. The woody fraction comprises the cellulosic material serving as a support for the plant. The impurities in the juice comprise crystallizable or non-crystallizable reducing sugars, organic materials and inorganic materials. Ammonia nitrogen is in the form of traces; the pH of the juice is of the order of 5. Molasses are viscous liquids with a density of 1.4 to 1.5 and whose pH is of the order of 6. They contain a significant amount of reducing sugars, i.e. more than 25% of the sugar fraction. Ashes can represent 5 to 6% molasses.
Production statistics for Guadeloupe and Martinique
The production of cane is expressed in tons, that of rum in hectoliters of pure alcohol
1.2. LA FERMENTATION STRICTLY SPEAKING
1.2.1. The microflora in fermentation media.
Work in pure culture with given microorganisms is not practiced. Yeasting is carried out from a stock tank stocked with natural flora. An average value is given to the cell population by generally adding baker’s yeast. Several authors have commented on the strains that can be found in the rum industry. Pairault (1899), Kaiser (1916) identified Saccharomyces and Schizosaccharomyces. We have made an inventory of the yeast flora on the one hand to identify all the species present and on the other hand to select later those with good rum skills. Samples were taken at three levels: on the raw material, in the tank in full fermentation and on the wine. With suitable dilutions, two Petri dishes containing Wickheram medium at pH 4.5 were seeded. The different colonies were taken. The identifications were made following the method of Lodder and Van Rij. The survey was conducted during the 1970 campaign. It involved ten facilities on molasses and sixteen on cane juice. Two hundred colonies were analyzed. In addition to cryptococci, which do not ferment sugars and are contributed by earthy particles, the main recognized species are the same as those that El Tabey Shehata (1960) has shown in Brazil. Saccharomyces aceti and Saccharomyces chevalieri are important wild yeasts because of the number of times they are reported. Schizosaccharomyces pombe is present in musts leading to ‘grand arôma’ rum. In all other cases, Saccharomyces cerevisiae is the main fermentation agent for molasses and cane juice. The results of this survey are shown in Table 4.
Presence of yeast species in fermentative environments. The number in the column represents the number of times that the yeast is corresponding (*) (*) Is reported in the medium considered.
Isolated yeasts Raw material Must Wine fermentation wine
In fermentative media, yeast concentrations are low. The corresponding dry matter often represents less than 1 g/l. The aeration systems in the tanks are poorly adapted to give a good multiplication of the agent chosen for the fermentation. Also, on cane juice, wild yeasts sometimes present in abundance, use some of the sugars and ammoniacal nitrogen. More seriously, they can supplant Saccharomyces cerevisiae in poorly maintained facilities.
The information available on bacteria in fermentations of molasses and cane juice are fewer. Kervegant (1946) reports the presence of acetic bacteria and butyric ferments. Maurel (1965) noted a high relative propyl alcohol content and traces of secondary butanol, facts that may suggest the intervention of bacteria in the manufacture of “grand arôma” rums. Reported sugar losses were linked by Tilbury (1970) to lactobacilli activity. We have with Dubois (1973) highlighted, in an agricultural rum acrolein derivatives that come from the metabolism of bacteria.
1.2.2. The pH.
The pH of the molasses is about 6, that of the cane juice 5. The pH values found in the fermentations are of the order of 4.5. They are acquired by addition of sulfuric acid and by the action of the acids contained in the yeast starter. Molasses has a high buffering capacity. In the laboratory, we found that for molasses concentrations of 200 g/l, 2 g/l of pure, concentrated sulfuric acid was required to increase the pH of the solution from 5.8 to 4.6. At the end of the fermentation, the ph drop is about one unit. These values of ph theoretically should protect fermentations against bacterial attack. This is not the case, as is shown by the amounts of volatile acids produced during the fermentation and the microscopic presence of many bacteria, even if they are not all active.
1.2.3. Total acidity and volatile acidity.
On rums from Martinique analyzed by gas chromatography, Nykanen (1968) found that acetic acid accounted for 75-85% of the volatile acids. For the remaining fraction, the propionic, butyric, caprylic and capric acids each represent about 3%. The other saturated fatty acids are in varying proportions. Unsaturated fatty acids are in trace amounts.
Table 5 shows the average acid values of molasses and cane juice.
The inhibition of yeasts by acetic acid results in decreases in the fermentation rate, the number of yeasts produced and the amount of fermented sugar. This is a well-known fact since the Muller-Thurgau experiments in 1885. Table 6 shows similar results obtained on a molasses fermentation at 100 g/l of sugar (Parfait, 1970).
Average values of acidities in fermentations of molasses and cane juice
Influence of acetic acid on fermentation of molasses
Culture medium: molasses q.s.p. 100 g/l sugar, ammonium sulphate 1 g tap water q.s.p. 1.000 L
Initial population in yeast (S. cerevisiae strain Berlin l) 2 X 10 ^ 6 / ml initial pH: 5 – Fermentation temperature: 28° C Fermentation time ten days
The fermentation rate is expressed in grams of fermented sugar in 24 hours in one liter of medium
The volatile acidity of the must without the addition of acetic acid is 8.2 mg/l.
Many factors and in particular the ecological conditions, the stage of maturity and the variety considered affect the nitrogen content of canes. Almost half of this amount remains in the bagasse after grinding. In cane juice 0.015 to 0.5% is found in nitrogenous matter. The mineral part and in particular the ammoniacal nitrogen is in the form of traces.
On molasses from Guadeloupe from different plants and collected at different times, we did the determination of total nitrogen (Kjeldahl method) and ammoniacal nitrogen (displacement method by magnesia). On average, the molasses used have 48 mg of ammonia nitrogen and 3.28 g of total nitrogen per 100 g of product.
The amount of nitrogen supplied by the raw material must be supplemented with a source derived from either mineral (phosphate and ammonium sulphate) or organic (urea) sources. Measurements made in factories show that in less than 24 hours the ammoniacal nitrogen has disappeared. We studied in the laboratory the use of some nitrogen compounds. The tests were conducted with Candida utilis. The samples are removed from the yeasts by centrifugation. Ammonium ions are assayed after being displaced by magnesia. Urea is assayed enzymatically. In a Warburg apparatus, in buffered medium at pH 5, the release of carbon dioxide produced by urease is measured. The results are shown in Table 7.
Use of some nitrogen compounds, yeasts.
Culture medium: yeast carbon base 11.7 g, sucrose 100 g, nitrogen source, water q-s-p. 1,000 ml.
Fermentation temperature 28 ° C. Both ammonium polyphosphate I and II have different origins.
We have also found that the sharp and sudden drop in pH with ammonium sulphate hinders cell multiplication. If after 24 hours the pH is reduced to 5.2 with potash, the cell multiplication after a new latency phase resumes an exponential pace.
1.25. Sugar concentration and ethanol formation.
The Creole columns accept wines from 4 to 5° GL. Under these conditions, must concentrations are often less than 100 g/l in total reducing sugars.
There are three phases in the formation of ethanol. The formation speed gradually increases, it then takes an exponential pace, finally, it gradually decreases. After 30 hours, almost all the ethanol is formed. The by-products and in particular the higher alcohols form in parallel curves to those of ethanol. The non-alcohol of the rums has a great importance in the constitution of the aroma; it leads to choosing certain working conditions. To lower the higher alcohols, low sugar concentrations have been adopted. The figures giving the yields of the fermentation reflect the double desire to obtain the maximum of alcohol from the sugar and a non-alcohol corresponding best to the desired product. According to the Gay Lussac equation, 51.11 g of pure alcohol are obtained from 100 g of sugar.
Pasteur has established that secondary products are also produced and that the alcohol figure should be reduced by 5%. The theoretical yield is then 48.55.
We have estimated the performance of fermentation operations in an agricultural distillery. Figures range from 35.82 to 41.77 grams of pure alcohol per 100 grams of sugar. On average, the fermentation efficiency is 75 to 80 % in agricultural distillery.
There have been three generations of distillers in the French West Indies. The first stills used double distillation with recycling. In the following Systems, a bubbler or a condenser was introduced to obtain an alcoholic beverage on the first run. The continuous columns were modified in the French West Indies to give Creole columns accepting a wine of 4 to 5o GL. The losses in the vinasses are normally low. The characteristics of the column and the flavor of the product during distilling enable the operator to define and control the quality of the product obtained.
The fermentations of molasses and cane juice present particular aspects to the French West Indies. Cane juice occupies an important place among the raw materials. The production of traditional rum tends to increase while that of cane decreases for various reasons. Organoleptic analysis can recognize the characteristic flavor of rums, but it is not used rigorously to distinguish different types. The chemical analysis reveals a fairly great heterogeneity in the values taken by the non-alcohol constituents. The quality of raw materials, the conditions of distillation and especially those of fermentation are partly responsible for the aroma.
This traditional production of the French Antilles gives an important place to the art of the operator. The parameters of the fermentation were fixed either according to the natural conditions (temperature, flora) or according to the characteristics of the installation (apparatus to be distilled) or according to the quality of the product (addition of ammonium salts, low concentration in sugar) or according to simple bacteriological rules (acidification of the medium). However, it can be seen that all this does not guarantee the obtaining of a given product under regular conditions. These parameters must be defined according to more stringent criteria. Non-alcohol components are formed during fermentation. They each have a particular importance in the aroma. It will be necessary to study the mechanisms of their formation and to determine the factors which are responsible for their rate of presence in rums. From there, we will set the values of certain parameters of fermentations. Yeast plays a key role in the development of aroma. The selection of strains, fairly good producers of ethanol and responsible for a particular aroma is to be made. Seeding at high levels of population under good aseptic conditions should be sought. Some products at very low concentrations in the rums contribute greatly to the aroma. The various means of analysis, in particular those of gas chromatography associated with mass spectroscopy, will have to be used to make their inventory. We will then study their origin and the circumstances of their presence at a certain rate in rums.
This traditional production of French West Indian rums represents only a small share of the world market. Light rums predominate largely on the latter. Generally, the production of these light rums uses: the treatment of the raw material, the use of selected yeasts, fermentations with must rich in sugars (130 to 150 g / l), distillations following precise techniques in continuous columns. There is more and more problems of manufacturing these products in the French West Indies. Several solutions are studied, the choice of which will be best suited to the French West Indies can be facilitated by the knowledge acquired in the field of traditional fermentations. We think in particular of the precise inventory of the substances of the aroma and the control of the contents with higher alcohols. We have accordingly oriented our research work in these directions.
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