Prof. S. V. Lebedev and N. G. Zabegalov.

Study of the Conditions for Drying Sugar Beet for Its Processing in the Sugar Industry

Sugar-beet production, combining within itself agriculture, large capital, and diverse manifestations of industry—such as quarrying, machine building, transport, etc.—is a powerful factor in the country’s economic development. The importance of sugar-beet production, from the very first years of its existence, was correctly understood and duly appreciated by the state authorities of various countries, by science, and by private capital, which everywhere invariably devoted much interest, attention, and support to this new branch of industry, thereby promoting its rapid growth and development. At the present time the beet-sugar industry, having taken shape as the modern sugar factory with an average daily capacity of 3–4000 berkóvets of beet, deeply affects local agriculture, promoting its high advancement. However, territorially such influence of the modern sugar factory is extremely limited. The chief reasons for this lie in the properties of the raw material being processed—the sugar beet. As is known, the latter contains about 75% water. Under such conditions, delivery of the beet from the place where it is sown to the factory involves a large unproductive expenditure on the transport of approximately four times, in comparison with the sugar contained in the beet, the quantity of water.

In addition, the high water content makes the beet a perishable product. Under favorable storage conditions, the beet nevertheless inevitably loses part of its sugar. Moreover, in the best case this loss over a month fluctuates around one percent by weight of the beet; i.e., in 2–3 months of good storage under favorable conditions, the beet loses up to 17% of the initial sugar content in it.

During transport by cart or by railway, while lying at loading points, and during transshipments, sugar beet incurs losses incomparably greater than during factory storage in clamps.

In view of the noted characteristics of beet, modern sugar production is compelled to be seasonal, with a very short campaign of 2–3 months, after which the factory remains idle for 10–9 months. Under such circumstances, the fixed capital invested in the enterprise is utilized very poorly, while overhead expenses increase greatly.

The desire to increase the simultaneous load of the factory by expanding the territory served by that factory with distant beet sowings also encounters insurmountable obstacles beyond a very small distance from the factory. According to the data of agronomist A. P. Korkhov, based on practical data from large estates of Kharkov Province for 1910–1914,^1 already at a distance of 5 versts, transport by cart of sugar beet over a good dirt road costs about 15% of the gross expenditures on this crop, including overhead and general expenses, or about 33% of

^1 Korkhov—The Role of Large and Small Farms in Supplying Sugar Factories with Beet, p. 96.

of direct costs. With an increase in distance this cost rises approximately as follows, as a percentage of the gross outlay:

at a distance of 5 versts . . . . . . 15%
» » 10 » . . . . . . 25%
» » 20 » . . . . . . 40%
» » 30 » . . . . . . 50%

i.e., when beets are delivered over 30 versts, the transport costs amount to half of the entire annual gross outlay and considerably exceed the sum of all the other direct expenses for the cultivation of sugar beets.

A certain correction, though not a very significant one, is introduced into the possibilities of a modern beet-sugar factory by its location directly on a railway line. In this case the factory’s sphere of beet procurement expands by virtue of beets delivered from separate railway loading points, which are, as it were, the outposts of an already existing center of beet cultivation fertilized by the factory. However, this circumstance does not weaken, but even, when the campaign is drawn out, contributes to an increase in the losses of sugar in the stored beets.

Thus, the forced short duration of the work of a beet-sugar factory and the extreme limitation of its sphere of influence by the surrounding agricultural territory are characteristic features of modern beet-sugar factories. Moreover, these distinctive features are at the same time the weakest sides of the beet-sugar industry, sharply limiting its further growth and spread.

The principal reason for this lies, as has already been established, in the excessive moisture content of fresh beets. In this connection there naturally arises the idea of the possibility of dehydrating the beets immediately after their harvesting, in order to make delivery to the factory cheaper and to ensure successful preservation until factory processing, without the losses of sugar during storage that are inevitable for fresh beets.

The method of preserving beets by drying them was proposed in Germany by Schützenbach as early as 1850.

After that, the indicated idea from time to time attracted the interest of individual researchers. Separate patent applications also appeared, both abroad and in Russia, for the drying of sugar beets. However, up to the present century this idea aroused not only no practical application, but not even interest on the part of sugar factories.

An idea of how the practical application of the method of drying beets to the conditions of factory operation was envisaged is given by individual patents, for example, by the patent of the Zographos brothers.¹ Their method of preserving sugar beets was as follows: beet shavings are treated with sulfurous acid, or with formaldehyde vapors, or with similar substances, after which the shavings are dried directly in the open air to a content of 10% water. After this, the shavings, thus partially dried, are finally dehydrated in a steam drying apparatus at 80–90°.

According to Sopoćko’s patent, the beet shavings, upon leaving the beet slicer, are subjected to the action of sulfurous gas, which dissolves cold in the juice of the cut beet cells. After this the shavings are sent to a drying apparatus, where they lose up to 50% of water by weight.

Upon leaving the dryer the shavings are sprayed with a solution of sodium fluoride. With such treatment the shavings, according to the author of this patent, can be kept for a very long time without spoilage or loss of sugar.

Theorists of the sugar industry, in the idea of processing dried beets, were chiefly interested in the possible changes of sugar and, in general, of dry

¹ “Privilege for the Zographos method of preserving beets,” 1906, 31 pp.; N. Z. E. I. S. Pr. 1927, VIII, p. 254. Benin.

substance forming part of the mass of the beet root, as well as the losses associated with this.

A. Herzfeld and Schrefeld¹, working with beets grated into pulp, dried the latter at 108° in a vacuum, and also in air at 70°, 100°, 120°, and 160°. It was found that the quantity of dry pulp obtained from the dried cossettes by washing out from them all that was soluble with cold and then hot water changes depending on the drying temperature. The smallest quantity is obtained by drying at 100°. As the temperature is raised to 130°, the quantity of dry pulp increases by 32%, and at 160° by 35%, as compared with the quantity obtained from cossettes dried at 100°. Lowering the drying temperature to 70° also causes an increase in the insoluble mass of the pulp by 40% as compared with the quantity corresponding to drying beets at 100°.

This phenomenon, in the opinion of the investigators, is connected with the transition, depending on the drying temperature, either of the insoluble pulp of fresh beets into soluble compounds, or with the reverse transition into the insoluble state of certain constituent substances of the beet cell sap. As for the behavior in the drying process of pure washed beet pulp, the latter withstands even prolonged drying at high temperatures, for example up to 167° for 15 hours, changing almost neither quantitatively nor qualitatively. When pure beet pulp is dried in the presence of sugar, it decomposes much more readily, and this phenomenon begins already at lower temperatures, which, in the opinion of the investigators, is due to the interaction of pulp and sugar under drying conditions.

Classen² notes that, during the drying of beets, processes of decomposition of their substance take place.

N. Karavaev and A. Palkin dwell on the question of whether, during the drying of beets, there will be a decrease in the sugar yield as a result of possible inversion, and, on the other hand, whether dried beets will acquire properties that hinder the diffusion of sugar from them. Their experiments were conducted directly in the sun, and also at temperatures of 60° and 100°. The data obtained lead the authors of the study to the conclusion that, in terms of the losses occurring during drying, there are no obstacles to working with dried beets.

In one of the most recent works carried out in the same direction, G. Benin³, at the Kiev State Experimental Institute of the Sugar Industry, judging from the investigator’s words, sets the task of “establishing the most favorable conditions for the process of drying beets.” The drying temperature in this case is taken as 100 and 120°. The duration of drying ranges from 12 to 1 hour. The conclusions obtained are summarized as follows:

1) The longer the duration of drying, the greater the sugar losses in drying beet cossettes: at 12 hours the losses amount to 1.82% of sugar; with one-hour drying they decrease to 0.1%.

2) Greater decomposition of sugar is accompanied by a greater accumulation of invert sugar, but the degree of accumulation of the latter does not correspond to the quantity of sugar lost, which indicates further decomposition of the sugar being formed.

3) Drying may be carried out at temperatures above 100°, but in doing so it is necessary to carefully monitor the condition of the cossettes during drying, since keeping the latter too long after all the water has been removed from them entails an increased loss of sugar.

4) The quality of the cossettes during drying, especially at temperatures above 100°, is of very great importance. The quantity of pulp must be minimal, since the latter dries more quickly than the rest of the mass of cossettes and therefore may burn.

5) The most favorable conditions for extracting and determining sugar from dried beet by the method of hot-water digestion are 85–90° with a digestion time of 60 minutes.

In the twenties of the present century, industrial interest began to appear in Italy in the possibility of factory processing of beets dried by the de Vecchis method¹. In connection with this, in 1924, somewhat south of Venice, at Loreo, a sugar factory was established whose purpose was to demonstrate the economic feasibility of the indicated method.

The factory is financed by neighboring beet growers. The capacity of the factory is 100,100 tons of beets annually. Drying is carried out by a current of heated air. The beet cossettes pass successively through six sieve belts arranged in chambers. Air heated to 130° is directed under the upper belt with fresh cossettes, where, moving slowly, they remain for 20 minutes and are heated to 130°. Upon reaching the end of this belt, they fall onto the nearest lower belt. The latter, like the four belts lying below it, moves at half the speed in comparison with the first belt.

The air temperature changes successively. Proceeding from the upper belt to the lower one, the air temperature on the individual belts is determined as follows: 130, 120, 110, 70, 80, and 90°.

Evidently, the fourth and fifth belts serve to cool the cossettes, since, on leaving the last belt, the cossettes had a temperature of 90° at a moisture content of up to 5%. All the information cited about the factory at Loreo is taken from the report of the commission of Bowden, Goodwin, and Owen, sent from England by the Ministry of Agriculture and Fisheries to Italy to acquaint themselves with the method of sugar production under factory operating conditions.

According to other sources of descriptions of the same method of drying beet cossettes found in the literature, one can find other drying temperatures given by various authors of these descriptions; thus Teseni² gives 80–100°, Sani³ 90–100°.

Comparing the data available in the literature on the temperature conditions of drying sugar beets, it may be seen that different investigators do not take the maximum heating of them to be the same. The temperature fluctuations are very considerable and range from 60–70° to 130° and higher. Moreover, temperatures exceeding 100° are already recognized by all as threatening caramelization and burning of the sugar and other constituent substances of the beet-root mass.

The difference in the aims pursued by individual investigators, and the divergence not only in temperatures but also in the majority of the other conditions of drying sugar beets, rule out the possibility of drawing any definite conclusions on the basis of direct comparisons of the results of studies of this kind.

In connection with this, the basic question of the optimum temperature for drying beet cossettes remains, to a considerable extent, open even to the present time, although the proposition that it is inadvisable to raise the temperature of the beet mass being dried to more than 100°, as well as the necessity of drying with heated air, must already be considered proven.

It is obvious that not only the limiting degree of heating of the cossettes being dried, but also the course of development of the heating, and also the gradualness connected with this—

and the sequence of increase in dehydration over time must have a substantial significance with respect to the quality of the resulting dry beet mass.

The criterion for the conformity of the temperature conditions to the requirements of rational drying of sugar beet is the assurance that the dry cossettes can be easily and completely extracted of the sugar contained in them.

Of course, this is under the condition of the fullest possible transfer, without losses, of all the sugar of the fresh cossettes into the dried product, and provided that the drying method corresponds to economic requirements in terms of fuel consumption.

In the work presented below, the task was set to trace how the process of dehydration of beet cossettes develops when they are dried by a current of air heated from 45 to 85° C, and how the drying temperature affects the possibility of extracting sugar from the dry cossettes.

The temperatures for drying were taken from 45 to 85° C. The lower temperature limit was adopted as one below which further reduction appears already inexpedient, since in industrial drying tasks the requirement is advanced of a certain rapidity in completing the process. Raising the drying temperature above 85° appeared undesirable until it had first been clarified how, in the opinion of individual investigators and according to patent-literature data, this temperature—already excessive and supposedly harmful for drying beets—affects the process.

In all the experiments described below, the beet cossettes were dried by a current of previously heated air. The drying was conducted in a wooden drying cabinet with 11 shelves, of the system of Prof. S. V. Lebedev. Heating of the air washing over the beet cossettes lying on drying plates placed on the shelves of the cabinet was carried out by an electric heater. Each shelf is provided with a thermometer. On the upper shelf of the cabinet an exhaust pipe with a ventilating device is installed. Air is supplied to the apparatus from below and, passing the air-heating chamber and the shelves with cossettes, is led into the ventilating pipe. The air current and the degree of heating of each individual shelf are maintained in the apparatus throughout the experiment without change, and quite steadily.

In observing the development of the drying process, the plates with the cossettes being dried were weighed every hour, from each shelf separately. The accuracy of weighing was up to 0.1 g, with a load on each shelf of 300 g of fresh beet cossettes.

Each shelf of the drying apparatus corresponds strictly to an established temperature attainable for the experiments.

The dried cossettes are collected shelf by shelf, in separate fractions, corresponding to the drying temperature. The dried cossettes are stored in glass jars with ground stoppers.

The material for the study was sugar beet grown near the city of Tomsk in 1927 from seeds of the 1923 harvest, obtained from the Tetkino variety-seed station of Kursk province.

The washed and dry-wiped beet was cut with the aid of an ordinary knife of a factory beet slicer, placed in a knife frame and set for a cossette thickness of 3 mm. From the total quantity of cossettes prepared in this way, thoroughly mixed, in each experiment 4 samples were taken to determine the average sugar content in the fresh cossettes. The remaining quantity of cossettes was placed, 300 g per plate, on each shelf of the drying cabinet, previously heated to the required degree and quickly loaded with the prepared and weighed beet samples.

The successive change in temperature by the shelves of the drying apparatus, i.e. the drying temperature of the separate fractions of the beet cossettes being dried, is presented in Table I below. In the same table are given

the duration of drying of the cossettes required to remove, at various drying temperatures, 76–78% of the water from fresh cossettes. In this case, the dry cossettes obtained amount to about 22–24% of the initial weight of the fresh beet cossettes taken for drying.

TABLE No. 1.

The following Table No. 2 presents data showing how, over time, the process of dehydration of beet cossettes develops when they are dried by a stream of dry air at the various temperatures indicated below.

TABLE No. 2.

Table No. 3 presents the results of another series of experiments on drying beet cossettes, carried out under the same temperature conditions as before, but with a different air flow.

TABLE No. 3.

Hourly loss in weight of fresh cossettes, as % of the initial weight, over the time from the start of drying

The data presented indicate that both an increase in the drying temperature and its prolongation lead to an increase in the absolute amount of moisture removed. In this sense, the duration of drying and the degree of heating can, to a certain extent, compensate for one another.

However, the significance of each factor for the individual stages of drying proves to be unequal. The predominant importance of an elevated drying temperature, which is sharply manifested in the initial stages of dehydration of sugar beet, decreases rather rapidly with time. Owing to this, after a certain interval of time, moisture loss begins to proceed equally both at a high and at a comparatively low temperature.

It is evident from Table No. 3 that during the first hour of drying at 55°C only 2% evaporates, whereas at 88°—24.6% of moisture from the weight of the fresh beet cossettes.

Thus, at 84° these cossettes lose 12.3 times more than at 55°, whereas in the third hour of drying the same ratio is expressed as 4.3, in the sixth hour as 1.3, and in the seventh hour as only 0.9. The latter indicates that drying at 84° during this period already proceeds more slowly than at 55°.

Considering in connection with this the data of Table No. 2, it can be seen that during the final-drying period the time factor acquires predominant importance over the factor of the height of heating.

From a comparison of the corresponding data of Tables Nos. 2 and 3, it is evident that at the same drying temperatures the dehydration process may be carried out very differently with respect to the moisture content and the duration of the individual drying periods.

Obviously, this circumstance must be connected with the course, duration, and degree of intensity of the various physical, biological, and chemical processes unfolding in the material being dried. Consequently, the order and conditions of drying must have a certain influence on the quality of the product obtained.

On the other hand, the drying conditions must, to a certain extent, be determined by the nature and individual properties of the material being dried.

Proceeding from this, one may expect that the development of dehydration processes, for example, of sugar beet and potatoes, may proceed in the individual stages not quite identically for these two products of plant origin. This may take place in the final stages of drying potatoes and sugar beet. Then, in both cases, different conditions are created for the dehydration process. This is due to the fact that in beet at this time a highly dense, already difficult-to-concentrate sucrose solution is being evaporated, whereas in potatoes, where the starch is not in solution, the release of moisture during this period of drying proceeds with much greater ease.

The correctness of this proposition is confirmed by Table No. 4, where experimental data obtained during parallel drying of beet and potato shavings under completely identical conditions are compared. This comparison was carried out for the various temperatures of interest to us.

TABLE No. 4.

From the data of Table No. 4 it can be seen that, under the conditions taken, the drying rate of beet in the initial stages noticeably exceeds the rate of the same process for potatoes. But already in the period of 5–7 hours the intensity of dehydration of sugar beet begins to lag noticeably, and by 7 and 8 hours this is already a general situation within the range of temperatures and conditions considered.

The findings established indicate that the drying temperature is determined by the individual properties of the material being dried. The temperature of the shavings being dried throughout the entire drying period, depending on the stage of drying, must change, gradually decreasing toward the end of dehydration.

An excessive increase in temperature in the final stage of drying is inexpedient.

The degree of drying of beet shavings at a higher temperature increases more rapidly than at a lower one.

Turning to the question of the influence of the drying temperature of beet shavings on their capacity for desugarization, we shall first dwell on the research method applied in the present case.

The nature of this method is determined, first, by the endeavor to approach the question from the standpoint of the possibility of factory processing of dried beet, with

on the other hand, to find a method which, by its nature, would be sufficiently close to the usual industrial extraction of sugar from beets by the diffusion method. It is obvious that under such conditions the extraction of sugar must be carried out with water. However, as to how this should be done with dried beet, the literature gives only very meager and far from complete indications. Concerning the degree of heating, the duration of extraction, and the quantitative ratios of water to dried beet, there are only statements by individual authors, tied to the accidental conditions of particular laboratory investigations, without the aim of industrial extraction of sugar from dried beet.

In this connection, for example, in the work of Benin,¹) the dried beet is finely ground. It goes without saying that this method, quite correct for the laboratory study of dried beet chips for their sugar content, is entirely unsuitable for the industrial extraction of sugar from dry beet. The reasons are clear: first, an increase in the cost of production due to the expense of grinding the dry beet; second, a certain deterioration in the aqueous sugar extracts obtained, since with fine grinding an excessively large number of beet cells are opened. In this case all their contents pass entirely either into solution or into a difficult-to-separate colloidal and suspended state, hindering the subsequent purification of the sugar juices obtained from ground dry beet.

Under such conditions, extraction by the diffusion method directly from dried chips has the advantage of simultaneously purifying the extracted sugar, without at the same time interfering with the completeness of its extraction. Therefore, in the present work all the dry beet chips, in exactly the same way in all trials, were sorted on a system of sieves, whereby all flour, fines, and also excessively coarse chips were separated. As a result, only a homogeneous mass was obtained, consisting solely of chips of identical thickness. This same method of cleaning the dried chips at the same time also contributed to the correctness of selecting the average sample.

In the first part of the present work it was established how, under completely identical drying conditions at different temperatures, 8–9 fractions of dried beet were obtained. In the present case these samples are to be compared with respect to their capacity for desugarization. This can be done not only by applying one and the same method of investigation, but also by applying it under completely identical conditions, which is guaranteed by the simultaneous and joint treatment of the compared samples of dry beet.

Under such conditions, obtaining one or another percentage of extracted sugar from separate samples of beet chips dried at different temperatures makes it possible, irrespective of the method chosen, to obtain entirely comparable results. In view of the above, experiments on extracting sugar from dried beet were conducted jointly and simultaneously for all 8–9 compared fractions of beet chips of different drying temperatures, changing in individual cases the extraction temperature, its duration, etc., simultaneously for the entire series of compared samples.

Turning to the extraction of sugar itself from dried beet, the following should be noted. The sugar was extracted by the method of aqueous digestion at various temperatures, with the highest at 90° C and the lowest at 20° C, for durations from 15 to 45 minutes, in addition to preliminary trials with durations of 60 minutes and more.

Comparison of the results of experiments with durations of 60 and 45 minutes showed that, for dried beet, by the extraction method applied in the present work

¹) N. Z. G. E. I. S., Pr. 1927.260.

60 minutes already offer almost no advantage over an extraction duration of 45 minutes.

The weighed portion of dry beet in most experiments was taken as 5.2 grams, for a digestion flask volume of 200.6 c.c. This corresponded to the conditions for extracting sugar from fresh beet with its normal weighed portion of 26.0 per 200.6 c.c., since in drying beet about 80% of the water is removed from it.

Under such conditions, the results obtained in determining the sugar content of dry beet could be compared directly with the results of the ordinary determination of sugar in fresh cossettes.

Taking a larger weighed portion of dried beet for the usual volume of the digestion flask seemed undesirable and inconvenient, since the volume of the swollen beet pulp would be disproportionately large compared with its normal volume in the corresponding sample with fresh beet cossettes in an analogous determination.

The actual experiment on extracting sugar from beet was carried out by the method described below.

Before the digestion flasks were placed in the bath, the latter was brought exactly to the required temperature, which was strictly maintained throughout the entire experiment.

The water in the bath was stirred by a current of air passed through it.

The flasks, being suspended in the bath, were freely washed by the heated water. All the prepared flasks were placed in the bath simultaneously. The initial filling of each flask corresponded to 3/4 of its working volume. Digestion was carried out without the addition of lead acetate. The latter was added, after the extraction of sugar was completed, to the already filtered liquid before polarization, in the usual proportion of 10 per 100 c.c.; accordingly, the reading obtained in the polarimetric determination was also increased. During the experiment, the contents of the flasks were mixed at short intervals by shaking, without removing them from the water of the bath. Each flask was filled up to the mark 15 minutes after the start of digestion.

At the end of digestion, the flasks were simultaneously and rapidly cooled to 20° C; their contents were filtered through a dry filter and, after clarification, polarized in a 200 mm tube. The result obtained was doubled, a correction for dilution by the addition of lead acetate for clarification was introduced, and everything was converted by recalculation to the fresh cossettes from which the tested dried material had been obtained.

Each test was conducted in 2 parallel samples.

In addition to the results of chemical analysis, the appearance of the dried cossettes themselves is of interest, chiefly: the coloration, the change in shade, and the degree of color in individual samples as a function of the drying temperature of the cossettes. The color is of interest both for the dried cossettes themselves and for the liquid obtained after digestion and filtration of the extracted cossettes.

It was found that the duration and the temperature changes of digestion, within the limits of the experiments considered, had almost no effect on the color of the juices obtained.

The color of the dried cossettes ranged from earthy gray with a slightly violet tint to the color of strong liquid tea, at 84° drying, with a transition through intermediate colors to a yellow-brown shade at 74–79° C.

The observed change in the color of the dried cossettes indicates that processes of noticeable caramelization and destruction of the substance of the dried beet cossettes begin at 76–79° C and are already clearly manifested at 84° C in beet drying.

The correctness of this is confirmed by changes in the color of sugar juices obtained by digestion of various samples of beet cossettes dried at different temperatures, as presented in Table No. 5.

TABLE No. 5.

The data of Table No. 5, while revealing the destruction in general of beet substances when it is dried at a temperature of 85°, also definitely indicate the destruction of sucrose at this temperature. This is seen from the fact that instead of 15.4% sucrose obtained from beet cossettes dried at 60° C, in the case of drying at 84° only 14.4% sucrose is obtained. The sucrose content established for cossettes dried at 41° C and found to be only 14.0% indicates that lowering the drying temperature to 41° C makes it difficult to extract from the dry cossettes the sugar contained in them. Thus, a drying temperature of 41° C is too low for drying cossettes, whereas 84° is too high.

Subsequently, the influence of the drying temperature of beet cossettes and the significance of the digestion temperature of the resulting dry cossettes were systematically determined by a series of experiments, the data from which are presented below, compared in Table No. 6. The conditions of these experiments were as follows: duration of digestion, 15 minutes; digestion temperatures from 20 to 90° C.

Considering the data of Table No. 6, it should be noted that there are certain fluctuations in the results of parallel samples. This discrepancy should be attributed to the fact that, despite the utmost care in mixing both the raw material going to drying and also the dry beet cossettes taken for the sample, individual samples of it, taken in an amount of 5.2 g, still cannot be completely identical in their composition, since the element of these samples is an individual cossette, having a rather large weight for the given size of chemical sample and its own quite definite individual composition.

However, despite the discrepancies in the composition of individual samples noted above, a general comparison of the successive change in the quantities of sugar extracted during digestion, in connection with the influence of the digestion temperature and the drying temperature of the beet, gives a quite definite picture, leading to a number of interesting propositions on the question under consideration.

These propositions are as follows:

1. A low drying temperature of beet slows the extraction of sugar;
2. The amount of sugar extracted during short-term digestion (15 min.) increases with an increase in the digestion temperature;
3. With digestion for 15 minutes, a digestion temperature of 80° C is already insufficient for extracting all the sugar from dry beet cossettes.

TABLE No. 6.

Conditions for drying beet pulp with 15-minute digestion at a temperature in °C

1. A beet-drying temperature of 84°C lowers the degree of sugar extraction and partly destroys it.

2. For more complete extraction of sugar from dry beet cossettes with short digestion, 15 min., at about 90°C, the most expedient drying temperature lies at about 74–79°C.

In the following tables Nos. 7 and 8 analogous data are given for conditions corresponding to the experiments of table No. 6, with the difference that table No. 7 corresponds to a digestion duration of 25 min., and table No. 8 to 45 minutes.

In all these tables, the content of sugar extracted in individual experiments from digestion of dry cossettes is converted into percentages of sugar in the fresh beet cossettes subjected to drying.

The data of tables Nos. 7 and 8 confirm all the propositions already revealed in the analysis of table No. 6.

In addition, a mutual comparison of all three named tables leads further to the conclusion that, with lengthening of the digestion time from 15 to 45 minutes, the degree of extraction of sugar from dry cossettes increases. This increase, sharply apparent at low digestion temperatures, is somewhat reduced when the temperature of the latter is raised. But even around 90°C this increase in the degree of sugar extraction is still quite clearly manifested.

The corresponding comparison of the influence, on the degree of sugar extraction, of the duration of digestion of dried beet is presented in table No. 9 according to the mean data of tables Nos. 6–8 for the cases most definitely revealed.

To a somewhat lesser degree the same phenomenon is also observed for digestion temperatures from 30 to 50°C.

One of the essential aspects of the possibility of processing dried beet is connected with the question of sugar losses during the drying of beet cossettes.

To clarify this, determinations of sugar were made in fresh raw cossettes and in the same cossettes dried at various temperatures. The determination conditions in both cases were taken to be identical. The method of hot aqueous digestion at 90°C was applied, with a duration of 45 minutes. For fresh cossettes a normal charge of 26.0 g was taken; for dry cossettes, the charge corresponding to it was 5.2 g, also for 200.6 cubic units of digestion volume, i.e., equivalent quantities of raw and dry cossettes were taken. The latter, both in this and in all other experiments, before working with it was carefully separated on sieves from all fines and dust, and also from excessively large cossettes, using only cossettes without pulp, exceptionally uniform in thickness. This circumstance, as already noted earlier, was the reason why the dry cossettes obtained had a somewhat different (more high-quality) composition than the raw ones. The reason for this is that the pulp, consisting of fragments of the covering tissue of the beetroot, cell walls, fibers, etc., is poorer in sugar than the remaining mass of beet cossettes. As a result of this screening, the cossettes proved on average, for 80% of the comparative tests made, richer in sugar than the corresponding average sample of fresh cossettes. In numerous determinations it turned out that the sugar content in raw cossettes ranged from 10.9% to 13.3%, and averaged 11.5% sugar, whereas for dry cossettes, recalculated to raw material, these figures varied within the limits from 12.1 to 13.3%, with an average content of 12.3%. Thus, for the reasons already indicated, in the case under consideration the erroneous impression is created that more sugar is obtained from dry cossettes than from raw. In reality, however, sugar losses during beet drying are inevitable. Moreover, beginning with a drying temperature of 84°C, caramelization and destruction of sugar already begin to appear, reflected in the distinctly manifested increased coloration of the digestion liquors at this drying temperature, which is completely not observed for cossettes dried at lower temperatures.

TABLE No. 7

Conditions for drying beet cossettes at a temperature of 25 minutes of digestion at °C

TABLE A No. 8.

TABLE No. 9.

A more detailed clarification of the question of sugar losses during the drying of beets in the present case could not be carried out, owing to the consumption of all the initial material.

Sugar losses in processing dried beets are connected not only with drying, but also with the extraction of sugar from the cossettes. At the same time, in addition to the digestion temperature, the duration of extraction of the latter is of importance for the completeness of extraction and, along with this, for the possibility of sugar losses.

In the preceding section, the duration of digestion of dried cossettes was examined within a time range of up to 45 minutes. In this it was established that the optimum digestion temperature corresponds to 90° C. The question, however, of how completely the sugar of the dry cossettes is extracted in the course of 45 minutes remained still unresolved.

It therefore appeared necessary to set up digestion experiments of longer duration.

This was carried out in three series of experiments with beet dry cossettes of different sugar contents, namely: 12.0%, 12.2%, and 16.2%, calculated on raw beets. All samples of these beets were dried at 66° C. Conditions: digestion at 90° C, sample weight 5.2 g per 200.6 cubic centimeters, duration of digestion from 45 to 95 and 115 minutes. The results of the experiments obtained are presented below, in Table No. 10.

TABLE No. 10.

Within the limits of the inevitable discrepancies, already noted above, in the composition of individual samples of dry pulp, the data of Table No. 10 show quite definitely that digesting dry pulp for 45 minutes at 90° C takes almost everything that can be taken from it with respect to sugar extraction.

Increasing the duration of digestion under the indicated conditions beyond 65–75 minutes already causes losses of sugar.

Conclusions.

The experimental data obtained make it possible to draw the following general conclusions regarding the conditions for drying beet pulp by a stream of heated air and regarding the requirements for the most rapid and complete extraction, by the digestion method, of the sugar contained in it.

1.—A low drying temperature slows the extraction of sugar.

2.—A drying temperature of 84° C already partly causes decomposition of the sugar and somewhat hinders its extraction;

3.—The most favorable temperature for drying beet pulp lies within the range of 74–75° C;

4.—The best conditions for water digestion of dry beet pulp are 90° C with a duration of at least 45 minutes and at most 60 minutes.

1. “Report of the Commission on the study of the de Vecchis method of beet-sugar production,” Ministry of Agriculture and Fisheries, London, 1925 (translated from English). ↩↩

2. Proceedings of the Scientific Research Department of the Sugar Industry Trust, Kyiv, 1924, vol. I, p. 203. ↩↩

3. Ibid., 1927, p. 255. ↩↩