Kervegant Chapter XVIII Control Of The Manufacture

[This was a slightly tedious chapter. An important idea here is the testing of molasses for fermentable sugars using a very careful and idealized fermentation test. There is also an absolutely fascinating description of evaluating skimmings which at the time of writing may not even have applied to any distillery but Galion in Martinique. Many of the tests leave you with the idea that they require substantial economies of scale to execute. However, their may be much faster but no doubt costly modern alternatives.]

Kervegant Chapter XVIII Control Of Manufacture:

Pages 453-466


Practically, rhummerie control is almost always very rudimentary. It is generally sufficient to determine the quantity of raw materials used and volume of rum obtained, to calculate an empirical yield, which is related to the ton of cane or hectolitre of molasses. In addition, control operations during manufacture are usually limited to raising the density of musts before and after fermentation. It is only if the yield is too much lower than the norm that one decides to carry out the evaluation of the sweet substances existing in the must, sugars and the alcohol remaining in the vinasses.

[Alcohol would remain the vinasse mainly through errors during continuous distillation.]

With this way of doing things, considerable losses may go unnoticed, which would be easy to avoid with more control over the manufacturing process.

This must include the analysis of the raw materials used, the control of the fermentation and that of the distillation. In addition, if the distillery uses cane juice directly or after processing into syrup, the mills must be inspected.

Control of mills

Various formulas have been advocated to make it possible to appreciate the efficiency of mill work. The most commonly used are: mill extraction, extraction coefficient, saccharose-ligneous coefficient (“milling loss” to English authors) and undiluted juice lost in the bagasse per cent of ligneous or, more briefly, lost juice (“lost juice”, “verloren sap” of the English and Dutch authors):

The extraction formula, for general use, has the disadvantage of being affected by errors resulting from weighing the canes and their juices. In addition, results obtained vary according to the nature of the cane handled, and particularly according to the content thereof in ligneous. The first objection remains for the extraction coefficient. As for the sucrose-ligneous coefficient, if it is simple to establish and does not require the determination of weight or volume, it is strongly affected by the errors in the determination of the polarization of bagasse and it varies according to the saccharine richness of the cane.

[For starters, I’m not sure if I should translate ligneous to lignin or pulp. Apparently for the sucrose coefficient they are doing heavy lab work involving polarization which would be important for projecting how much value could be extracted as table sugar.]

The criterium considered by many authors, and especially in Java, as the most satisfactory is undiluted juice lost in the bagasse % of ligneous. The brix of the bagasse being generally expressed by:

[could bagasse be a measure of something wet while lignin would imply dry?]

[That imagine is in error from my usual format. The text in the center reads:

the % juice lost in the lignin formula becomes:]

The ligneous % of bagasse is obtained by subtracting dry matter from the Brix of the bagasse.

The calculation of the previous formula requires determination in the laboratory of the following elements: Polarization of the bagasse, Polarization and Brix of the juice of the last mill, Brix of primary juice (juice expressed before the beginning of dilution), dry matter of bagasse.

[Often the juice gets diluted with water along the way as the canes are rinsed and re-pressed to extract more sugar.]

Sampling and analysis of bagasse.

Sampling. — The sampling of the bagasse is a rather delicate operation. As a result of the structure of the cane’s unequal distribution of water imbibition and grinding worse at the ends of the rolls, the bagasse layer composition is not regular. Samples should therefore be taken over the entire width of the conductor and throughout the thickness of the layer.

For certain evaluations, bagasse should be further divided, by means of a meat-grinder or special machines (Boot and Krantz, Athol, Warmouth-Hyatt, etc.). According to Norris, the maximum diameter of the pieces of bagasse should not exceed 6 mm for the determination of sucrose. During the operation, unfortunately there is a significant loss of moisture. To avoid the resulting errors, it is important to operate as quickly as possible and analyze bagasse promptly after collection, minimizing the duration of exposure to air (closed box storage). If there is desiccation that can not be avoided, take the necessary steps to determine it and take it into account.

The number of samples to be taken and analyzes to be carried out, so as to obtain relatively accurate information on average bagasse composition, depends on variations presented by the various analyzes, which are themselves a function of the variable composition of the raw material, the regularity of the diet, etc. It is usually necessary to take a sample every hour or at least every 2 hours.

[I’m not sure how they adjust the mill, but there is a lot to be lost if they are running too fast and missing sugar and running too slow and burning fuel. A percentage of sucrose is also inverting so if sugar is to be made, everything needs to be quick.]

Evaluating moisture. — The bagasse can be heated to a relatively high temperature, without appreciable decomposition, it is advisable to operate at 130° C to save time.

In Java and the Hawaiian Islands bagasse is placed in a thin layer in small, shallow trays holding 20 to 50 gr of matter. To obtain, on such a low weight, an average sample, the material must be finely divided. As moisture loss occurs during this division, some authors (Spencer, Deerr) prefer to operate on much larger quantities of bagasse (1-2 kgs) as it comes out of the mills. For this purpose, large, steam-heated or electrically heated ovens (Spencer’s oven) are used.

Determination of sucrose. — The bagasse is subjected to an aqueous digestion and the sugar, contained in a determined volume of water, is determined by polarization. Various procedures are in use.

In the method of simple digestion, 100 g of finely divided bagasse are placed in a tinplate cylinder. 100 cc of water and 5 cc of a 5% solution of sodium carbonate are added. It is maintained for 1 hour at the boiling temperature, allowed to cool and the container weighed. The liquid is then separated from the bagasse, then defecated with neutral lead acetate and polarized to the 400 mm tube. We take into account, in the calculation, the moisture of the bagasse, Let P be the weight of the apparatus filled with bagasse and water, p that of the empty apparatus, 55% the moisture content of the bagasse , the weight of the sweetened liquid (in gr.) will be: P – p – 45.

[45 is becauuse you started with 100 grams and assumed a moisture content of 55%]

In the Zamaron method, 100 gr of finely divided bagasse are placed, with 200 cc of water, in a metal basket placed inside a copper container equipped with a tap for the flow of the liquid. The water and bagasse are boiled for 10 minutes and the extract is collected in a one-liter flask. The operation is repeated 7 times, after which extraction of the sugar is considered complete. Lead acetate is added, the volume of the liquid obtained is raised to 1000 cc and polarized.

Evaluation of ligneous. — The ligneous can be determined directly by drying in an oven the residue obtained in the sucrose assay by the method of successive exhaustions. More often, however, it is indirectly determined by subtracting the Brix of the dry matter from the bagasse, which corresponds approximately to the Brix of the juice of the last mill. We then have:

Ligneux % bagasse = Mat. dried % bagasse – Brix juice last mill

Analysis of juices, scums and molasses.


Sampling. — It is essential, for carrying out control of the mills and to determine the quantity of sugar entering manufacture, to take samples representing the average composition of the juices. The sampling of the primary juice (undiluted juice, extracted by the shredder and the first mill) and the juice of the last mill should preferably be done by means of automatic devices, of which there are various models. That of the mixed juice, or diluted juice (juice extracted by all the mills, mixed and sent to the distillery), will be made by regular sampling in the measuring tanks. The total number of average samples will be at least one every 2 hours.

Automatic sampling devices, vases, funnels, measuring devices, must be kept perfectly clean, to avoid infections causing deterioration of the samples. Sampling devices will be steam disinfected several times a day, vases washed with boiling water, then rinsed with formalin solution and dried thoroughly after each use. Therefore, it is important to have two sets of instruments, one in use and the other be washed and disinfected.

When the samples are not analyzed immediately, and in particular when making composite samples for the determination of polarization or reducing sugars, an antiseptic must be added to the juice. Samples for the determination of brix or ashes may be supplemented with formalin (03 – 0.5 cc per liter) or, better, with mercury dichloride (0.5 cc of saturated solution per liter of juice). Those to be used for the determination of sucrose or reducing sugars receive powdered neutral lead acetate (20 gr per liter). In the case where composite samples are made, by successive additions of new quantities of juice, antiseptic must be added successively, stirring well each time to obtain a homogeneous mixture.

Juice analysis. — To control the mills, it is important to determine the Brix and Polarization of the primary juice and the juice of the last mill, at least once every 6 hours. After taking the Brix samples, taken once an hour or once every 2 hours, a certain amount of liquid (e.g. 50 cc) is poured into a vial to form the polarized composite sample.

In order to calculate the quantities of sugar used in manufacturing, the Brix and Polarization of the mixed juice are also determined in the sugar factories every 6 hours. In addition, evaluation of the reducing agents is carried out once every 24 hours on a composite sample. If there are appreciable variations in the nature of raw material passed to the mill, the frequency of analyzes will obviously have to be increased.

[I think the fear is that if reducing sugars increase, it is a sign that people down the road are not hustling to get the cane to the mill. Valuable sucrose will be lost.]

In the distilleries, analysis of the mixed juice can be carried out in the same way as in the sugar factory. Since it is appropriate to express the sugars as reducing sugars, the figure provided by the polarization will be increased by 5% (conversion factor of sucrose to invert sugar) and the average amount of reducing agents measured on the composite sample of the day. It is more logical, however, to directly measure the total reducing agents of the mixed juice. If the analysis is a little more delicate, it provides more accurate results. Determination of total reductants is necessary when the cane is imbibed with vinasse, which determines, because of its acidity, a certain inversion of the sucrose during extraction.

[I’m trying to follow this, but I suspect we are talking fresh juice that is cut vinasse and not exactly molasses, but I don’t see why molasses would not also apply. This kind of analysis could be important to formulating a precision batición that harnesses osmotic pressure to select for and promote a yeast in a spontaneous fermentation environment. These days I think we could use spectroscopy.]

Determination of density. — It is usually done using the Brix or specific gravity hydrometer. The juice is poured through a sieve of fine wire cloth into a test tube which is filled to the edges. Let stand for ten minutes in order to allow the air bubbles to rise to the surface, before plunging the hydrometer into the liquid. The temperature is recorded by means of a thermometer, in order to effect the density correction.

Determination of the polarization. — A 100-110 cc bottle is filled with juice up to the 100 mark, then add enough lead acetate to clarify the liquid, complete the volume to 110 with water. It is agitated, filtered, rejecting the first liquid and polarizing with a 200 mm tube. The polarization is given by the formula:

where N is the degree read by the polarimeter, D the density of the liquid (at 15° C) and W the normal weight.

More simply, one can operate as follows, using the Spencer pipette (1). After taking Brix from the juice, fill the pipette to the observed Brix degree and receive the liquid in a 100 cc bottle. Add 3-5 cc of lead sub-acetate solution, make up to 100 cc with water, mix well and filter. Polarize the liquid in the tube of 200 and divide the number obtained by 2 to have the polarization for 100. This procedure cannot be used with juices supplemented with Pb acetate unless Brix is taken on a sample of the juice without antiseptic or stored in mercury dichloride.

(1) The Spencer pipette is a pipette graduated so that filled up to the mark corresponding to the Brix (not corrected) of the sweetened liquid, it contains 2 times the normal weight of the liquid. The normal weight adopted is generally that of 26 gr. The graduation goes from 5° to 25° Brix.

[Preservation agents can skew the results..]

Evaluation of reducing sugars. — If the juice sample for analysis does not contain antiseptic, it can be simply filtered with kieselguhr, without using lead acetate, or any other defecant. Before the addition of kieselguhr, it is advisable to treat the juice with Na acetate (0.25 gr per 100 cc of juice) in order to eliminate calcium salts. Mercury chloride-preserved juices can be treated in the same way, but those with formalin should never be used for glucose determination, as formalin reduces cupric salts.

In the case of juice samples supplemented with dry lead acetate, according to Harris, results similar to those obtained by the treatment of fresh juice filtered with kieselguhr are obtained by the following method. It is added to well mixed, but unfiltered juice, 0.75 gr of powdered oxalic acid per 100 cc of sample, mixed well, allowed to stand a few minutes and filtered.

Mc Allep and Cook recommend clarifying juice (preserved with mercury bichloride) with neutral lead acetate (1 gr of solution per 10 gr of juice). After filtration, add, to remove the salts of Pb and Ca, 3 cc of a solution containing, per 100 cc, 3 gr of disodium phosphate and 3 gr of potassium oxalate. The glucose is then measured by the Eynon and Lane method, by using 25 to 40 cc of juice.

The direct reducers of the juice are thus obtained. To obtain the total reducing agents, the sucrose of the clarified juice is inverted and the salts of lead and lime are removed, if necessary. The sweetened liquid must be neutralized after inversion with a dilute sodium hydroxide solution, before titrating with Fehling (see determination of total reducing agents in molasses).

Scums. [skimmings]

Samples of scums that are not analyzed immediately are generally supplemented with lead subacetate (24 cc per 100 g of material), after dilution with water to a paste consistency to have a sufficiently intimate mixture. It is also possible to store the scum in an atmosphere of ammonia or chloroform: the sample is placed in a closed container, whose lid carries, attached to its inner part, a sponge saturated with a mixture of 6 parts of chloroform to 1 of ammonia. This process is also sometimes used for the preservation of bagasse samples.

Sugar is in the scums in the free state, that is to say soluble, or in the state of insoluble sucrates.


To measure the free sugars, we can operate as follows: we weigh 25 gr of scum (15.75 gr in the case of French polarimeters), which is kneaded in a glass mortar with hot water, so as to get a clear porridge. This is poured into a 100 cc flask and the mortar rinsed with hot water. After cooling, 6 cc of lead sub-acetate is added, complete to 100 cc with water, shake, filter and observe via saccharimeter. The degree read corresponds to the percentage of sucrose in the scums. Weigh only 25 gr of material, instead of the normal weight, to take into account the volume occupied by the insoluble matter of the scums.

Total sugars are obtained by decomposing the sucrates with acetic acid. To do this, add to the test portion, reduced to the state of a clear slurry, a few drops of phenolphthalein and then acetic acid dropwise until complete saturation. Continue then as before.

[Acetic acid combines with the bases of the sucrate liberating the sugar.]


The complete analysis of molasses shall include the determination of Brix, apparent and actual sucrose, reducing sugars, acidity, minerals, gums, nitrogen and phosphoric acid. For the control of the manufacture, one can be satisfied to take the density and to evaluate the total reducers. The determination of acidity, ashes, nitrogenous matter and phosphoric acid, however, provides interesting indications, both as regards the value of the raw material in the distillery and the ingredients to be added to the must (sulfuric acid, ammonium salts, phosphates).

Determination of Brix and density. — The viscosity of molasses is too high for it to be possible to directly determine density by means of a hydrometer. Under the conditions of industrial practice, a certain amount of molasses is dissolved in an equal weight of distilled water, and it is on this solution that Brix is taken. Temperature correction is made in the usual way and the number found is multiplied by 2 to obtain the undiluted molasses Brix. This way of doing things gives numbers that are too high.

One can also take the density of the molasses, by the Sidersky process, and obtain the Brix using the concordance tables.

Actual Brix is determined by desiccation of molasses on pumice or quartz sand, preferably operating in a vacuum oven (study by Spencer), at a temperature of 70°.

Determination of sucrose. — In order to obtain the apparent sucrose (direct polarization), the normal weight of molasses diluted 1: 1 in a 100 cc flask is usually introduced by Spencer’s pipette. The amount of lead sub-acetate needed to clarify, complete to the mark, filter and polarize in a 200 mm tube is added. Multiply the number observed by 2, to have the polarization. If molasses is very colorful, it is better to take only the normal weight.

For real sucrose (Clerget), use the Jackson-Gillis method n° 4. Introduce the normal weight of molasses into a 300 cc bottle and fill to the mark. Pour the solution into a test tube, add enough dry lead acetate of Horne, mix well and filter.

Evaluation of reducing sugars. — Weigh 5 gr of molasses sample, previously well mixed, and diluted with water to 500 cc. The weight is lowered to 4.5 gr (3.5 for inverted syrups), if the molasses is high in sugar, and raised to 5.5 gr, if it is poor.

For the determination of direct reducers, take 50 cc of the above solution and measure with Fehling, using the Lane and Eynon method, if the rate of reducing sugars is not less than 20%, and the Browne, Morris and Millar method if not.

To have total reducers, place 50 cc of the 1% molasses solution in a 100 cc flask with 25 cc of water, and gradually add 6 cc of concentrated HCl (at 1.16 density), mixing well. Place the flask in a 70° water bath, shaking occasionally, so that the contents reach 67 to 69° in 2½-3 minutes; maintain this temperature for 7½ minutes. After having rapidly cooled to room temperature, saturate the solution with a 40% sodium hydroxide solution. Fill in the 100 mark and evaluate the reducing sugars, using the Lane and Eynon method.

In the above procedure recommended by Davis, the solution of molasses is examined as such without defecation with lead acetate or removal of lime salts. The results obtained would, according to the author, be about the same as those provided by defecated and decalcified molasses.

However, according to other authors, it would be advisable, if one wants to have precise figures, to subject the molasses to a special treatment, before making the Fehling liquor titration. The solution is fairly well clarified by adding kieselguhr to it and 0.25 gr of dry sodium oxalate; filter and complete to 500 cc (Spencer). One can also defecate with neutral lead acetate (0.3 cc per gr of molasses) filter, remove lead and calcium salts, adding 1 cc of a solution containing 7% disodium phosphate and 3% potassium oxalate (Cook and Mc Allep) per gr of molasses.

Evaluation of unfermentable reducing sugars. — Various methods have been recommended by L. de Bruyn and A. Van Eckenstein, Maquenne, Pellet, Waterman and Van der Ent, etc., for the determination of unfermenting reducing sugars. Correct in principle, they give rather irregular results.

In practice, it is possible, as proposed by Davis, to determine the reducing sugars remaining in the fermented mash used to determine the yield of alcohol. Place 50 cc of this solution in a 200 cc flask, neutralize the acidity with a soda liquor, add 5 cc of alumina cream, complete to the mark and stir. After filtration, the reducing sugars are evaluated in the usual manner.

[Very clever! I always wondered how these were measured.]

In the absence of liquid used to determine the alcohol yield, Davis advises to operate as follows. Prepare a solution of 500 cc, containing 20% molasses, add 1 gr of ammonia phosphate and acidify the mixture with dilute sulfuric acid, so as to have a pH of 4.4 to 4.6. Ferment the solution to 33° C with pure yeast. When fermentation is complete, neutralize carefully, add 10 cc of alumina cream, dilute to 1 liter and determine the reducing sugars as indicated above.

[I am wondering if there is any fermentation based method to practically evaluate fermentable sugars in various molasses. Basically you would have a standardized ferment with a standardized yeast and then count the ethanol and acids produced.]

Evaluation of acidity. — Titrimetric determination of acidity can only be done by the touch method, because of the dark coloring of the molasses. For the same reason, pH determination is also possible only with the potentiometer.

[Luckily we have modern pH meters!]

Assay of ashes. — Determination of sulphated ash is done on a sampling of 3-4 gr of molasses, by the method previously described.

To obtain carbonated ash for the complete analysis, it is possible to operate as follows. Place molasses in a large platinum capsule, mixing it with pure olive oil or petroleum jelly to prevent overflow during heating. Then heat until inflammation of the mass. Once it is sufficiently charred, pulverize it in a glass mortar. Rinse the powder obtained with hot water, on a paper filter without ash. Incinerate the insoluble residue and filter it into the platinum capsule. Evaporate the filtrate to dryness, and bring to dark red to get rid of organic matter. The ashes obtained are subjected to the complete analysis, according to the methods of the quantitative analysis.

At the time of addition of sulfuric acid, it is important to observe the odor that emerges: one can thus detect the possible presence of the  sulfur compounds (sulphites, for example), if these exist in a notable quantity in the molasses (Arroyo).

[To my knowledge Arroyo only mentioned this in the context of the sulfuric acid test on spirits and I have observed this brimstone aroma myself. This particular context may point to another Arroyo work I haven’t found yet.]

Non-organic sugar. — Non-organic sugar is generally obtained by difference, subtracting from 100 the amount of sucrose, reducing sugars and ashes.

Of the non-sugar constituents, nitrogenous and phosphate materials are of particular interest because of the role they play in feeding the yeast. Their determination gives indications on the quality of the molasses as raw material of fermentation. Nitrogen is usually measured by the Kjeldahl method, and the figure obtained is multiplied by 6.25.

[This is definitely an area that needs elaboration.]

It should also be checked, by distillation with water, if the scent of molasses is pleasant. Old molasses sometimes contain organic acids (butyric, formic, etc.), which seriously impede fermentation.

To search for these acids, an excess of sulfuric acid is added to the diluted molasses, and about half of the liquid is distilled, maintaining a strong boiling. The distillate is neutralized with barite water, then carbonic acid is passed through the heated liquid, filtered, evaporated to dryness and weighed after 100% desiccation. Incineration of this residue gives Ba carbonate, that is transformed into sulphate of Ba by the sulphate of Am which one weighs. The quantity of organic acids is calculated from the difference between the two weights. These are sought in the distilled liquid by the usual methods (Duclaux, Werkman).

[Barite water is a new concept for me. It contains Barium. I’m not sure why these acids cannot just be titrated?]

Fermentative value of molasses.

The yield of molasses of the same saccharin richness varies considerably in proportion to the presence of infermentable reducing substances which are counted as invert sugar by chemical analysis. As there is no reliable method for the determination of infermentable reducers, the nature of which is poorly known and, it seems, very complex, the only way to determine the value of molasses as a distillery raw material is to make a fermentation test in the laboratory. We give below the method developed by Davis (1) to carry out this test.

(1) Int. Sug. J. XL, 235, 1938.

[This is surprising and and optimistic. I thought they had a chemical method and I would cheat by creating a fermentation method. Spectroscopy may have yielded new methods, but fermentation may be practical for a small operation. We should also track down that citation!]

Dissolve 200 grams of molasses (or a quantity sufficient to obtain a min with no more than 5.5% alcohol by weight) in 400-500 cc of water. Add 2 N sulfuric acid to bring the pH to 4.4-4.6 for ordinary molasses and 4.9-5.1 for invert syrups, and 25 cc of a solution containing 40 gr of Am phosphate (anhydrous) per liter and brought to pH 5.0 with sulfuric acid. Fill the volume to 1 liter with water. Weigh the bottle with the must; calculate the weight of 400 cc of must and take the density using the densitometer.

[What are we bring to a liter volume, our must or our Am phosphate solution? I suspect its the must because we proceeding to make two trials.]

Introduce into two 750 cc flasks Erlenmeyer, 400 cc of the above liquid, adding to each additional 4 drops of must to compensate for losses from successive transfers. From each 750 cc flask, pipette 2 cc and 20 cc of liquid into a test tube and into a 100 cc Erlenmeyer flask. Cap the 750 vials with a sulfuric acid closure (Meissl valve, Hayduck or Bauer stopper), the 100 cc flasks and test tubes with wadding. Pass flasks and tubes to the sterilizer for 1 hour at atmospheric pressure.

[These sulfuric acid closures are airlocks as far as I can tell, but he uses the acid later.]

Cool the test tubes, inoculate with a pure culture of yeast used in the distillery and place in an incubator at 33° C. After 24 hours, transfer the contents of the tubes to the 100 cc Erlenmeyer flasks. Keep them in an incubator for 24 hours and transfer their contents into bottles of 750 cc. Set up the valves and pour 2.5 cc of concentrated sulfuric acid into each one. Weigh the flasks (to the nearest centigram); let it ferment for 4 days and weigh again. Repeat the weighings daily, until the change in weight in 24 hours does not exceed 0.05 gr.

[A centigram is 0.01 grams. My question is whether any modern day prepared yeasts can negate the starter phase if we use a direct pitch method. At no point so far do they count cell density.]

Cool the flasks and take the density of the liquid using a hydrometer. Pour the contents of the sulfuric acid valves into a 100 cc flask containing ice and add 5 cc of 50% sodium hydroxide solution (100 gr in 100 gr of water). Transfer the fermented must and the contents of the valves into a 500 cc volumetric flask and make up to the mark with distilled water.

[So we are moving 400 cc of volume (plus possibly 20+cc from the air lock) from a 750 cc flask to a smaller 500 cc flask. I’m not sure what the ice did besides possibly make the reaction less violent.]

Measure 100 cc of the liquid (at 15° C) into a 100 cc graduated flask and pour into a distillation flask, rinsing the flask 3 times with a little water (no more than 35 cc total). Place about 5 cc of distilled water in the graduated flask where the distillate is received. Distill until about 95 cc have been collected and transfer the distillate to a second distillation flask with the sample bottle wash water. Alkalize the liquid with 12 drops of 50% sodium hydroxide solution and redistill in the same 100 cc bottle as before. Finally complete the volume at 100 cc and take the density using a pycnometer.

[The redistillation seems a little neurotic. I would have thought you would want the acids (neutralized before the second distillation) and possibly measure them because they somewhat represent potential alcohol.]

Using tables showing the correspondence of densities and alcoholic strength, we will determine the proportion of alcohol provided by the molasses. The fermentative value will be the percentage of this practical yield relative to the yield that would have been obtained if the total reducers had been wholly processed into alcohol. This value can vary, for cane molasses, between 80 and 90%, according to Davis.

It is also important, to realize the value of molasses for the production of rum, to make a steam distillation test, in order to determine the aroma of the product, which influences favorably or unfavorably the quality of the spirit obtained. The first 50 or 100 cc of the distillate will indicate the character of the natural aroma of the molasses examined.

[I do not think this test is well appreciated or that enough large producers have the choices they want. Certain molasses may have to be diverted to continuous column spirit while finer molasses may make pot still rum.]

Fermentation control

Juice sent to fermentation needs to be controlled from the point of view of its temperature, its density and its acidity. It is important to note, for each tank, the time of the beginning of the pouring and the end of fermentation: initial, intermediate and final densities; initial and final acidity. The temperature must be frequently raised and maintained at the desired degree. In order to be aware of the efficiency of fermentation, total reduction of the wort must be determined at the beginning and, when the vat has fallen, the remaining sugar and alcohol. Determination of alcohol corresponding to disappeared sugar shows whether the fermentation was normal, and that of the remaining sugar indicates whether it was complete. Finally, physicochemical control will be advantageously complemented by the microscopic examination of starters and fermented liquids.

Analysis of musts.

Evaluation of reducing sugars. — The richness of musts in sugar can be deduced from the composition of the raw materials (juice, molasses). However, more precise results are obtained by directly evaluation the total reducers. One can take 25 cc of must, which is introduced into a flask with 25 cc of water and 6 cc of HCl; invert, complete to 500 cc, neutralizing with soda, and titrate with Fehling.

For the determination of unfermented reducing sugars, take 250 cc of fermented must, remove the alcohol by boiling and, after cooling, return to the original volume by addition of water. Introduce 50 cc of the liquid into a 200 cc flask and invert with HCl. After cooling, make up to 200 cc and titrate with Fehling. If the liquid is too strongly colored, it can be treated with a little fine carbon black.

Determination of acidity. — Acids are evaluated the usual titration method, in the musts of vesou and syrup; by the method at the touch, in those of molasses. As for the pH, it can be determined colorimetrically or, more precisely, by means of a potentiometer.

In order to be aware of the good progress of fermentation, it is important to measure the initial acidity of the must and the final acidity. The increase in acidity during the fermentation must be low.

[This idea likely can be elaborated and taken beyond pH to titratable acidity. Different classes of rums will have different Δ’s of acidity and we will be mindful of the low value acetic “radical”.]

It may be interesting, in some cases, to separately assay the volatile acidity of the fermented must using Duclaux or Mathieu’s method.

[I described in the other analysis chapter, the updated UC Davis method with its optimized glassware.]

Duclaux subjected to distillation 110 cc, collected 100 cc and evaluated the acidity with soda, in the presence of phthalein.

In Mathieu’s method, 10 cc of wine are introduced into a 60 cc flask, then 18 cc of distilled water. We heat and distil 6 cc and, at this moment, 6 cc of water are added to the flask (by means of a graduated funnel). 6 cc of water are distilled again and continue until 24 cc is collected, on which the acidity is measured.

[This gradual addition of water must be done because of the low volatility of these acids. This can be seen with the birectifier where there is still appreciable acids in the stillage after distilling multiple 25 cc fractions of just water.]

Evaluation of alcohol. The methods used for determination of alcohol in musts are: ebulliometry (Dujardin-Salleron ebullioscopes, Malligand, etc.), which in practice quickly gives a close result; distillation, the method most commonly used, but which can only be exact by taking certain precautions; chemical evaluation, which, well done, gives rigorous results.

[Modern methods would be U-tube densitometry coupled with refractometry (which may rely on model building) and then inline spectroscopy which relies on rigorous models but can also simultaneously evaluate other variables.]

Distillation method. — To obtain accurate results, it is advisable to take a fairly large quantity of must (500 cc for example), which is neutralized with soda or potash in the distillation flask. If this neutralization is not carried out, the volatile acids would pass into the distillate and some of the alcohol would be esterified, giving esters, the density of which is generally higher than that of the alcohol.

Distilling slowly is requires, to avoid entrainment and to not hinder condensation. Cooling must be vigorous enough to bring the temperature of the distillate to about 15° C. Finally, it is important to extend the refrigerant by a tapered tube immersed in distilled water, to ensure the washing of non-condensable gases released at the beginning of the operation.

[I’ve heard of similar ideas but I don’t completely understand the specifics. I think the main gas in question is CO2 dissolved in the ferment. Is this almost like a water cooled reflux head before the condenser? I think “washing” may be the removal of entrained substances when the must “belches” CO2 at the beginning of the process.]

We must collect, according to alcoholic degree 2/3 or 3/4 of the volume used. It is recommended to receive the distillate in the measuring flask used to measure the must, and to adjust the volume with distilled water before taking the alcoholic degree. If the temperature of the distillate is different from 15°, it is necessary to make use of a correction table (table of the alcoholic riches). Take into account also, to make necessary corrections for the differences of temperature which can exist between the various liquids: must of the tank, distillate, etc.

Despite precautions taken, losses usually occur mainly due to entrainment of alcohol by carbon dioxide at the beginning of distillation. It has been reported on several occasions that the amounts of alcohol calculated in the laboratory still were substantially lower than those obtained industrially with continuous columns. Boidin (1), for example, observed that the difference between the two could vary between 3 and 8% and was almost always around 5 to 6%.

(1) Bull. Ass. Chim, XLVII, 377, 1930.

[I’m wondering if any of this can be minimized with gentle ultrasonic degassing while condensing before distillation is started. However, even the ultrasonic process can have entrainment.]

Chemical method. — The chemical evaluation method avoids losses and gives figures closer to reality. These are generally 4 to 8% higher than those of the physical distillation method.

[I’ve seen this used in research papers from the modern era, no doubt because the previously described errors still exist.]

To assay alcohol by chemical means, proceed as it is said later about vinasses, but distilling 20 cc of must previously diluted to 1/20 and collect 10 to 15 cc of liquid. The number of cc of the bichromate solution required to obtain the turn corresponds to the number of cc of alcohol existing in 100 cc of must.

[I’m a little lost on this procedure.]

Performance calculation.

Performance calculation. — The yield of alcohol can be established, either in relation to the unit of weight (or volume) of the raw material, or, more precisely, in relation to the weight of fermentable sugars entered in the manufacture. In the latter case, the amounts of alcohol existing in the must are compared with those that theoretically should have been obtained from the composition of the raw material. The percentage of practical yield versus theoretical yield reflects the efficiency of fermentation.

[Don’t forget, fermentable sugars was calculated by a very specific fermentation test.]

We often mean by theoretical output, the quantity of alcohol supplied by the transformation of sugar into alcohol according to the Gay-Lussac formula. 100 g of glucose correspond, under these conditions, to 51.11 g or 64.45 cc of absolute alcohol, and 100 g of sucrose to 53.79 g or 67.84 cc of alcohol. The theoretical yield is then calculated by multiplying the percentage of sugars (evaluated as reducing sugars) contained in the sweet liquid by the coefficient 0.6445.

In fact, the Gay-Lussac equation does not exactly translate the phenomenon of alcoholic fermentation, where besides ethyl alcohol, various secondary products are also formed. Also, we often adopt the figures indicated by Pasteur, that is, per 100 gr of glucose, 48.67 gr or 60.89 cc of pure alcohol. The yield is obtained in this case by multiplying the reducing sugars by the coefficient 0.61. However, we prefer to use the Gay-Lussac coefficient to that of Pasteur, to establish the theoretical output, which in fact corresponds to experimental results, being likely to be sometimes exceeded.

[The Gay-Lussac figure is better because it is never exceeded and can give a better basis for comparing ferments.]

On the other hand, in calculating theoretical return, it is possible to take into account either all reducing sugars existing in the must or only the fermentable sugars. Low and practically negligible in the case of vesou musts, the rate of unfermentable reducers can reach up to 12% of the total reducers in cane molasses musts. It is evident that it will not be possible to be fully aware of the efficiency of the work in the vat room, except by employing as a comparison the theoretical yield given by the fermentable reducers alone.

[This may be even more important as molasses continues to evolve with increases in refining efficiency. However I think it was important back in the day because some molasses saw a lot of heat creating unfermentable reducers. Way way back this was significant as must were distilled before they were fermented to dryness and then dunder was recycled was that enough time under heat to create more unfermentable reducers from the remaining sugars. Dunder in general may skew these numbers. As baticións get more elaborate, these things must be paid attention to.]

The most practical method for assaying these is, as we have already indicated, to carry out a fermentation test in the laboratory and to determine the sugars remaining in the fermented liquid.

This way of doing things has, it is true, given rise to criticism. It has been pointed out, in particular, that various races of yeast transform sugar more or less rapidly and produce greater or lesser quantities of alcohol, some of which ferment carbohydrates which others cannot attack. On the other hand, a fermentation can be considered as complete, while it continues slowly or has been thwarted by certain adverse factors.

[I’m wondering if this test should be performed with a particular yeast or your aroma-centric production yeast. A yeast taylored to the question may also give a nice metric to compare various production yeast to.]

However, if the fermentation test was carried out with the race or mixture of yeast races used in the distillery, and with a must whose composition is sufficiently close to those treated in the vat room, valuable information will be obtained for control of fermentation. Comparison between levels of residual reducers found in the laboratory test on the one hand and in distillery fermented musts on the other hand, will make it possible to fully evaluate whether fermentation in the vat room has been complete.

To accurately determine the alcohol content of fermented musts, determination of alcohol content must be carried out on a sample of fermented must. However, in industrial practice, it is most often based on the attenuation or density drop of the must. It is also in this way that the minimum yield of the musts is calculated by the management in order to control the distilleries.

[This is the initial gravity – final gravity method used by brewers who do not have lab stills. A lot of distilling is knowing when to invest time in elaborate methods versus using quicker proxies.]

The drop in density during fermentation results, for the most part, from disappearance of sugar and formation of alcohol. For saccharine richness between 1 and 16%, the decrease in density corresponding to 1% less sugar is constant and equal to 0.00384. Similarly, for alcoholic strength between 1 and 10°, the density decrease resulting from the addition of alcohol is on average 0.001386 per degree of alcohol. If an industrial yield of 60 cc of alcohol per 100 g of sugar is allowed, the decrease in density corresponding to the disappearance in the must of 1% sugar giving 0.6% alcohol by volume will be:

A density decrease of 0.01 (i.e. 1 degree governed by the French legal density meter) will therefore correspond to an alcohol production of:

If the density is, for example, 1.060 at the time of filling and 1.010 after the tank has completely fallen, the number of liters of absolute alcohol existing in each hectolitre of must is:

The empirical coefficient of 1.28, which is a function of the alcohol yield, only gives results of relative accuracy. In France, it was brought by the Régie to 1.3 and, in the French West Indies, lowered to 1.2. This last number is noticeably too low. Also, the efficiencies observed in the rhummeries are always higher than the regulated yield, unless serious fermentation accidents occur.

In the English colonies, the tax services generally admit the performance of one gallon of alcohol-proof (57°) per 100 gallons of must, for an attenuation of 5°.

Microscopic examination.

Microscopic examination gives interesting indications on the purity of the fermentations, the number and the state of development of the cells of the musts and starters. It is essential in some cases, especially to determine the nature of infections.

Direct microscopic examination makes it possible to detect the presence of butyric, lactic and acetic bacteria. However, it gives positive results only if the must or starter is very contaminated. In the case of mild infection, it is important to incubate a small fraction of the test liquids in an oven.

The search for wild yeasts is made by subjecting a few drops of must to sporulation on a block of sterilized plaster; wild yeasts form their spores more rapidly than the cultivated breeds. However, to differentiate in a precise way a given yeast culture, it is important to know its physiological properties (minimum sporulation time, etc.). Control will therefore be especially effective in distilleries that work with pure yeasts.

The determination of the number of yeast cells contained in the must is important to follow the course of fermentation and the development of starters. It makes it possible to know when the increase in yeast cells is complete; if enough cells have been provided; if the changes that have been made in manufacturing have led to an increase or decrease in cell formation, etc. We have seen previously how to perform the cell count, using the yeast counter.

[These days automated cell counters are common and affordable. Affordable microscopes have USB enabled cameras that can count cells using a cell counting slide with free software.]

Finally, the microscopic examination gives information on the age and the physiological state of the yeast, data necessary especially for the preparation of starters.

[I think you look for scarring which tells about reproductive cycles and the percentage of dead cells to understand their viability.]

The young yeast is presented in the form of cells arranged in a rosary, without vacuoles, with protoplasm without granulations. Maturity is recognized by the fact that cells are of the same size and full form, usually isolated. The membrane is thin, protoplasm homogeneous, not very granular, with a large vacuole. The old or altered cells have irregular, stunted forms, a thick, double-appearing, granular protoplasm, with several small vacuoles. Those who have undergone autolysis are transparent; their membrane is often torn, and the protoplama partly out. In cell decomposition, the protoplasm becomes darker, more liquid; the vacuoles gradually disappear, the plasma escapes from the cell walls and meets in the intercellular fluid in irregular lumps; finally, these also disappear and the walls dissolve.

[Wow! I’ve never seen a description like that in the distilling literature.]

The presence of dead cells is usually determined using methylene blue at 1 p. 1000. A droplet of 1/50 cc of the reagent is mixed on the slide with a droplet of 1/5 cc of the yeast dilution containing 80,000 cells per cc. The number of colored cells is counted immediately.

Indigo carmine can also be used at 1/30. 0.06 cc of the reagent is added to 1 cc of a yeast solution in a 5% sucrose solution, containing 40,000 cells per cc.

Distillation control

The control of distillation involves the examination of vinasses in terms of their alcohol content and their acidity. Unfermented sugars should also be determined if this operation has not been done on the mash.


The determination of acidity is particularly important in distilleries which practice vinasse cycling, the acid content of this liquid intervening to regulate the dose of sulfuric acid to add to the musts.

[Keep in mind, he is talking stillage/dunder acidity.]

The acidity of the vinasses is difficult to determine, because of the strong coloring of the liquid, which prevents operating other than the touch.

[In case your’re just tuning in, these problems have been solved by titrating using a pH probe to determine the end point. You still want to titrate. pH alone is not enough information.]

Evaluation of alcohol.

This assay is usually carried out by distillation. As there is normally very little alcohol in the vinasse (less than 0.02 with columns exhausting well), it is advisable to operate on a large quantity of liquid, a liter for example, which one neutralizes with soda and distills to obtain 500 cc. This quantity is distilled again, so as to have 250 cc and in the latter distillate, the alcohol is measured. One can use a simple distillation flask connected to a Liebig condenser, a small still (Du-jardin – Salleron, for example) or better a laboratory rectifier (Barbet, Lepage, etc.), which allows in a single operation to concentrate alcohol in the hundredth of liquid used. Determination of the alcohol from the distillate is carried out by means of a sensitive alcohol meter, pycnometer or Duclaux dropper.

However, if one wants to have precise results, allowing a rigorous control of manufacture, it is much better to make the alcohol determination by the chemical way.

Many authors have proposed methods for the determination of alcohol by oxidation. We will only describe Martin’s, modified by Boidin and Mariller.

Martin – Boidin – Mariller method (1) — It is based on the oxidation of alcohol in the acetic acid state, using the sulfochromic reagent, and on the determination of the remaining bichromate by the ferrous sulphate, in the presence diphenylamine as an indicator.

(1) Mariller (Ch.) et Grosfiley (I.) — Le contrôle chimique en distillerie. Paris, 1939.

Reagents. — a) Solution of bichromate: dissolve 33.832 g of Potassium bichromate (dried before use at 130°) in water and make up to 1 liter. 1 cc. of the solution corresponds to 0.01 cc of alcohol.

b) Ferrous sulphate solution: dissolve 135.31 g of ferrous ammonium sulphate in distilled water (deaerated by boiling), add 20 cc of SO4H2 and bring to 1 liter, 20 cc of this solution, which is oxidizable and must be frequently checked, corresponds to 10 cc of the chromic solution.

(c) Diphenylamine solution: Dissolve 1 gr of pure diphenylamine in 100 cc of SO4H2 at 66°.

[Here 66° is likely a density as brix for sulfuric acid.]

Operating procedure. — Introduce 50 cc of vinasse into a 150 cc flask equipped with an abductor tube without refrigerant, with an extension plunging into a ball absorption tube (Boidin caterpillar), containing 10 cc of bichromate solution and 10 cc of pure sulfuric acid. Heat, boiling slowly enough so that no bulb-tube steam is released, the liquid of which should not boil. Collect a distillate of at least 15 cc. Transfer the chromic solution to a stemmed glass, with the washing water from the abductor tube and the caterpillar. Add 200 cc of distilled water, 20 cc of ferrous sulphate solution and 5 drops of diphenylamine solution (2). Titrate the excess of ferrous salts with the solution of bichromate until turning violet. If n is the number of cc of bichromate, the quantity of alcohol per 100 vinasse (alcoholic strength) will be: n x 0.02.

(2) In the presence of an excess of ferrous salt, the solution is green: it then passes, by adding bichromate, to blue green, then to intense blue or violet. The turning point of the diphenylamine can be made more sensitive by adding to the mixture 15 cc of a phosphoric acid solution (150 cc of concentrated SO4H2 + 150 cc of syrupy PO4H2, diluted 1: 1). (Bottger).

[SOS This definitely needs some help and caterpillar is likely incorrect. This almost seems like its distillation with an air condenser and then something the distillate runs into. A google image search did not help.]

Evaluation of sugar.

In addition to previously indicated evaluation methods, it is possible to use the Strepkow Method (3) to search for reducing sugars in the vinasse, which is precise and does not require the prior discoloration of the liquid to be analyzed.

(3) Biochem. Z. 1937, p. 90.

It is based on the reduction, in an alkaline solution, of potassium ferricyanide to ferrocyanide. The ferrocyanide formed is assayed by bichromate of potassium hydroxide in the presence of diphenylamine sulphate as an indicator.

[SOS I’m hoping I got the logic correct there.]

Reagents. — a) Ferricyanide solution of K N/50: 6.6 gr of ferricyanide plus 40 gr of anhydrous Na carbonate in 1 liter of water.

b) Diphenylamine solution: dilute to 1 liter, with 5% sulfuric acid, 15 cc of a solution of 0.2% diphenylamine in pure sulfuric acid at 66°.

c) Solution of bichromate of K, at 1.5925 gr of bichromate per liter.

Operating procedure. — In a 250 cc conical flask, add 20 cc of the ferricyanide solution and 10 cc of the sugar solution (which should not contain more than 13.3 mg of glucose). Mix well and heat for not more than 15 minutes in a bain-marie. Then cool, add 15 cc of diphenylamine solution and titrate with dichromate. Do a blank test without glucose. 1 cc of dichromate solution corresponds to 1 mgr of glucose.

Calculation of losses.

Comparison of the quantity of alcohol existing in the fermented musts (determined on a composite sample) and that actually collected in the column gives information on losses experienced during distillation. These losses are the sum of the remaining alcohol in the bottoms not sent for distillation and in the vinasse; the alcohol passed with the phlegmasses (heads and tails of distillation), when there is a fractionation with a column; and finally the alcohol lost during the actual distillation. They are expressed in percent of alcohol originally present in the fermented must.

Finally, we will calculate the amount of alcohol obtained as a per cent of total sugars and per cent of fermentable sugars entered in the manufacture.

Rums trial

The control of the manufacture must include an analysis, at least summary, of the rum obtained. This will include the determination of esters and acids, the determination of obscuration and that of louching.

[Obscuration would be if there was caramel or barrel solids and louching would be similar to the demisting tests, so if the spirit becomes cloudy when diluted or chilled.]

Esters and acids are usually considered to play a major role in the constitution of the bouquet. We can practically, in the control of rhummeries, neglect the other non-alcohol constituents, whose determination is also much more delicate.

Obscuration, or the fall of apparent alcoholic strength, following the addition of caramel, is determined in the simplest way by the method of Tabarié, described in another chapter. It is given by the difference between the alcoholic degree of the eau-de-vie removed from its dry extract and the eau-de-vie as it is presented.

Finally, we notice the louching of the rum at dilution, by mixing it with twice a weight of water and allow standing for 24 hours in a test tube. Louching is generally due to the presence of essential oils due to an excessive exhaustion of the must or the use of a caramel too burned for coloring.

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