DE2209243A1 - Process for crystallizing fructose - Google Patents

Description

Physicist Dr. Walter Andrejewski Graduate engineer Dr.-Ing. Manfred Honko Graduate Engineer Lawyer files: 38 700 / us Hans Dieter Gesthuysen

4300 Essen, February 24th 1972 Theaterplatz 3

Patent application of the company SUOMEN SOKERI 0SAKEYHTIÖ Mannerheimintie 15
OO26O Helsinki 26 / Finland

Process for crystallizing fructose.

The crystallization of fructose from water presents a number of technical difficulties because of its high solubility the fructose in water. In addition, conventional crystallization by means of evaporation methods is poor because of the poor thermal stability of the fructose excluded.

Because the need for fructose has increased greatly in recent years, it means a considerable advance on

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Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz 3

to be able to produce a very pure, large crystalline area by simple crystallization from a water solution and thereby also to produce mechanically easy-to-handle pructose in an economically advantageous manner. All these Advantages are obtained by following the process of the present invention.

According to the present invention, the fructose becomes from the water solution crystallizes in that a small amount of fructose crystals of the same size as possible is used as the crystal elements in solution is added and that these seed crystals are allowed to increase in size. A formation of new crystals is thereby prevented that the distance between the seed crystals is kept suitably small and the temperature during the entire crystallization is precisely controlled. The spacing of the seed crystals becomes with the ratio of the seed crystal volume determined to the total volume of the solution. The volume of the solution is increased either continuously or in stages during the crystallization process so that the desired spacing between the seed crystals is maintained.

The invention relates to the crystallization of fructose from a water solution to form crystals of an average Crystal size from 200 to 600 / µm. In particular it refers to the crystallization of the pructose from a water solution whose dry matter content is at least around 90 percent by weight with the dry matter containing at least 90% by weight of pructose and the remainder of glucose.

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Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz 3

Water solutions of fructose with dry matter content in the range from 90 to 94 % and with the purity of said pructose in the range from 90 to 99 percent by weight are obtained by removing pructose from glucose by the process according to the co-pending patent application by Suomen Oy, No P 20 JJ 656.1, submitted on ZJ. July 1970, is separated.

So far, pructose has been crystallized from methanol. On the other hand, when the pructose is crystallized from the water, the difficulties are great because of the high solubility of the Pructose and because of its low thermal stability. The viscosity of concentrated water solutions of pructose is very high, and the viscosity cannot be lowered by increasing the temperature, because the pructose in the increased Temperatures becomes unstable, which would be necessary for a substantial reduction in viscosity. Under these circumstances the result is very small crystals, which are uneconomical to separate from the solution. Besides, drying is one Mass of small crystals heavy. Because of all of the difficulties described above, those skilled in the art have the crystallization of pructose from water on a commercially attractive basis has been considered practically impossible.

Due to the poor thermal stability of the pructose, conventional crystallization by means of evaporation is excluded. and the crystallization is, according to the invention, by lowering the temperature of the solution and, moreover, possibly made by evaporation.

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Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz 3

It is a purpose of the present invention to allow the fructose to crystallize from the water solution as large crystals cause which can be easily separated from the solution by centrifugation. Another purpose of the invention is Success in crystallizing the fructose as crystals of sufficiently large dimensions that they are free flowing, in which case their handling, e.g. weighing and packing, becomes easier. Another purpose of the invention is the crystallization of a fructose whose crystal size is very homogeneous and which is also very pure.

Fructose crystallized from methanol has hitherto mainly been used by the pharmaceutical industry, which deals with very small crystals less than 0.15 / m in size. The large crystalline fructose crystallized according to the invention is indeed a new product. Because the need for fructose has increased greatly in recent years, means it is a considerable advance in the art to be able to do so by simple crystallization from a water solution a very pure, large crystalline and therefore mechanically easy to handle fructose in an economically advantageous one Way to manufacture.

Compared to crystallization from methanol, it is another one Advantage that the product obtained is completely free of methanol, which is a poisonous substance.

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Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz 3

The above purposes of the invention are achieved according to the invention by first providing a water solution of fructose whose dry matter content is at least around 90 percent by weight and whose dry matter contains around 90 to 99 % of fructose. The temperature of the fructose solution at this initial stage is that at which the solution is saturated with respect to fructose, e.g. around 58 ° to 65 ° C. The fructose is then crystallized from the water solution by adding a small amount of fructose crystals of the same size as possible to the solution as crystal elements and allowing these seed crystals to increase in size while at the same time preventing the formation of new crystals. This is achieved by keeping the distances of the seed crystals suitably short and by carefully controlling the temperature throughout the crystallization so as to maintain an optimal degree of fructose supersaturation in the range 1.1 to 1.2. It has been found that as the average distance between crystals increases, so does the risk of new crystals forming. Similarly, with an increase in the degree of supersaturation beyond the optimal range, the risk of the formation of new crystals also increases.

It is further essential characteristic of the method according to the invention that the volume of the solution during the crystallization process either continuously or gradually

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Andrejewski, Honlce & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz 3

is enlarged. When crystallization occurs as multiple stages, i. as two or more successive stages, the rapidity of the formation of small crystals becomes essential diminishes.

When the crystallization is carried out as two or more stages, each stage can be carried out in a separate crystallizer in which case the volume of crystallization increases from stage to stage because of the increase in the volume of the solution will. Alternatively, crystallization of several stages can be carried out in the same crystallizer, its volume is equal to the solution volume of the last stage.

Adding 2 to 4 % by weight of the sugar mixture of a low molecular weight organic solvent such as methanol, ethanol or isopropanol reduces the viscosity of the solution as well as the solubility of the pructose. Thus, the crystallization and centrifugation of the pructose crystals can be improved.

A detailed description of the invention is given below. A two-stage crystallization is described which is carried out in two separate crystallizers. The task is to crystallize pructose from a water solution, the dry matter content of which is around 90 to 94 percent by weight and purity with respect to pructose around 90 to 99 % and in which the impurity consists of glucose. The result is crystals, the size of which is determined by means of the screen test

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Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz

hereinafter defined is 300 to 500 µm and the amount of crystal is 4-5 to 55 % by weight of the amount of dry matter. The purity of the finished product is greater than 99.5 # in terms of fructose.

Level 1 :

(a) The crystallizer No. I is filled with the pructose solution described in the previous section, the temperature of which is controlled to such a level that the solution is saturated with respect to fructose (t = 58 to 65 ^° C.).

(b) To the solution, a small amount of pructose crystals of as uniform a size as possible is added as crystal elements, either crystals of 5 to 10 μm as suspended in isopropanol or larger crystals, eg 80 to 100 μm, as dry. The amount of seed crystals (m) depends on the size of the seed crystals (d), on the amount of completed ones

Crystals (M) and of the desired crystal size (D) according to the following equation:

tn

tn

(c) The supersaturation of the solution with respect to the pructose is then increased by lowering the temperature, and a programmed temperature control ensures a maximum

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Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz

Male rapid crystallization causes without the formation of disruptive new crystal elements. The temperature program; depends on the purity and dry matter content of the solution used for crystallization, and these programs are compiled on the basis of experiments for different cases. The correctness of the program is checked by means of samples taken at certain time intervals from which the supersaturation of the mother liquor is determined and can be changed during the crystallization if necessary. It has been found that the optimal supersaturation with respect to pructose is in the range of around 1.1 to 1.2. The cooling programs are best calculated to maintain supersaturation within this range during crystallization.

(d) The crystallization takes 75 to 150 hours, after which the temperature of the mixture is 25 to J55 ° C, depending on the type of solution used. At the end of the crystallization stage, the amount of crystals is around 50 % of the weight of the dry matter content of the mixture.

Level 2 :

Crystallizer No. II is filled at the same time with the finished mixture obtained from the previous stage, and with a fresh solution, the temperature of which has been controlled to such a level prior to supply that it together with the mixture forms a mixture in which the mother liquor is saturated or somewhat undersaturated, with reference on fructose, is. After filling, a fine adjustment of the Temperature.

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The same measures are then taken as in points (c) and (d) of step 1. After the process has ended, the fructose crystals are separated from the liquid by means of centrifugation. The most suitable centrifugation machines are the machines of the type used to extract sugar. Because of the high viscosity of the mixture, a large centrifugal force is required. An inexpensive device has a drum diameter of 106 to 122 cm and a speed of rotation of 1400 to 1800 rpm. In a typical process, a 106 cm centrifuge machine is filled with 120 to 250 kg of fructose crystal mixture. The crystals are washed with water (1-2 liters for filling). When the fructose crystals leave the centrifuge, their remaining water content is around 1.5 % * The centrifugation time for each batch, including filling, centrifugation and emptying, is 10 to 14 minutes ) is 250 to 500 kg / h.

Horizontal cylindrical vessels with a diameter of 2 to 2.7 m are used as crystallizers I and II. They are well insulated on the outside to prevent heat loss. They are equipped with a continuous axle shaft on which spiral cooling tubes are mounted. The speed of rotation of the shaft is 0.75 to 1.5 rpm. The cooling surface is around 2.5 m ² / m ⁵ . The volume (length) of the crystallizer increases from stage to stage, depending on the final crystal size of the stage, as follows:

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Where V _{1 is} the volume of crystallizer I and V _{11 is} the volume of crystallizer II and d and d ^ are the final crystal sizes of stages 1 and 2, respectively. This arrangement gives indirect temperature control; the temperature of the circulating water in the cooling tubes is controlled, and because of the large Kiihlungsfläche a small difference is the temperature of the mixture and of the cooling water obtained (2 to 7 ⁰ C). A direct method for temperature control can also be used if desired.

Crystallization can also be promoted by the fact that water is evaporated from the mixture, for example by blowing warm dry air on its surface.

The table below gives values for actual crystallization.

Table 1 Stage 1 Level 2 10 nP 30 v? Volume of the crystallizer 13 to 40 to Total amount of pructose 150 h 110 h Crystallization time 290 / um 5OO jam Crystal size 6.3 tons 19 to Amount of crystals 16 - 18 to Centrifugation day

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Instead of two separate crystallizers, I and II, it is possible to use only one crystallizer. The crystallization can can also be carried out as more than two stages, e.g. as three or four stages or as even more stages, with a number of crystallization devices in accordance with the number of stages or only one crystallization device can be used can. It is also possible, as an alternative, to use a combination of the above two alternatives, e.g. a three-stage Process where steps 1 and 2 are in the same crystallizer and step J5 is in a separate crystallizer are executed. If a crystallizer is used for multiple stages, its volume must match the volume of the solution last stage to be executed. In such cases the crystallizer can, for example, point to a vertical shaft mounted on which spiral cooling pipes are installed.

The accompanying drawing gives a graphic representation of a two-stage crystallization in two crystallizers. The graph is from a factory scale crystallization of fructose from a solution of 87.5 % fructose, 4.5 % glucose, and 8 % water. In the drawing:

Fig. 1 shows the total amount of fructose and the amount crystallized Amount of fructose in tons in the system as a function of time if the total consumed Time is l80 hours,

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Pig. 2 shows the temperature of the pructose solution in C as a puncture currently,

Fig. 5 shows the crystallized amount of pructose in the system as a percentage and as a puncture of time,

Fig. 4 shows the crystal size of the fructose in the system in .mu.m as a function of time,

Figures 5A to 5H graphically depict the relationships which were employed during an expediency of the process of the present invention and

Fig. 6 is a continuous crystallizer.

The graph has been divided into five sections: Filling of crystallizer I; Crystallization in Crystallizer I (called pre-crystallization); Filling of the crystallizer II; Crystallization in crystallizer II; and centrifugation. In Fig. 1, curve A shows the total amount of fructose in the system and curve B the amount of crystallized fructose. Time 0 on the drawings is the time at which the supply of the solution to the crystallizer I begins.

The fifth section of the graph in FIGS. 1 to 4 relates to the centrifugation of the solution, the Contains crystals. As stated above, the centrifugation time for a filling of a typical centrifuge is

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Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz 3

yaw machine from 10 to 14 minutes for a complete sequence of filling, centrifuging and emptying. In the process shown in the drawings, two centrifuging machines with an output of 250 to 500 kg / h each were operated continuously until the crystals had been separated from the total amount. The total amount of crystal was 19 tons. For this reason, each drawing has a time span of around 20 hours for the centrifugation process. Regarding Figs. 4 and 4 show
the curves show a slight decrease in the amount of fructose crystals and in the crystal size, which occurs when centrifugation is switched on, and this is a reflection of the losses that
occur during the centrifugation step and especially during the washing of the crystals to remove the adhering solution.

In connection with the transition from Stage 1 (Crystallizer I)
to stage 2 (crystallizer II), where fresh solution of the same nature as the initial solution is added, a small part of the fructose crystals is dissolved (Fig. 1), the temperature rises (Fig. 2), the amount of crystals increases _/ calculated as a percentage of the total Mixture ^ considerably from (Fig. J5) and 3. the average crystal size becomes somewhat smaller (Fig, 4).

The method described above, in which the supply of fresh solution took place at the transition from stage 1 to stage 2,
can be modified so that fresh solution during the
Stage 1 is added continuously until the end of the stage,

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in which case there will be no further feed at the transition to stage 2. This procedure is called two stages but made in a crystallizer as follows:

Level 1 ;

In the crystallizer, a solution of 87.5% fructose, 4.5% of glucose and 8% water is supplied, the temperature of as high (65 ⁰ C) is that it is under saturated with respect to Pruktose. The amount of the solution is such that, together with the pructose crystals to be added as crystal elements, they make up a mixture in which around 15 % of the dry matter content are crystals. The solution is cooled to the saturation level and the necessary amount of crystal elements, the crystal size of which is around 100 µm, is added. For example, when the amount of the solution is 900 kg in which there is 83Ο kg of dry matter, 150 kg of crystal elements of 100 µm are added. The temperature is lowered to such a value (50 to 55 ° C) that optimum proportions, including the optimum degree of supersaturation in the range of 1.1 to 1.2, are obtained for the growth of the crystals, and the temperature becomes held immutable. Because pructose leaves the solution all the time due to crystallization, more solution must now be constantly added to the mixture so that the proportions should remain unchanged. The degree of oversaturation must remain within the optimal range. As the crystals grow, so does the crystal face, and so does the amount of pructose that is crystallized in a unit of time. the end

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for this reason, the speed of solution addition is continuously increased according to a predetermined program. When the crystallizer becomes full, the addition of the solution is stopped.

Level 2 :

This step is a cooling crystallization of the same type as that in point (c) of the first method given above described. The mixture is cooled from 50 - 55 C, until the temperature has been reached at which the amount of crystals is around 50 percent by weight of the total dry matter amount of the mixture.

A reference to Pig. 5 will explain the considerations above in stages 1 and 2 in more detail. The changes in the mixture weight in tons of dry matter, temperature, ratio of crystals to the total mixture, crystal size, the speed of crystallization, the purity of the mother liquor, the degree of supersaturation and the dry matter content of the mother liquor all described with curves throughout the process. It should be noted that at the end of stage 1 the crystallizer is entirely is filled and that the optimal crystallization conditions during stage 2 by lowering the temperature of the mixture are maintained so that the supersaturation with respect to the pructose is kept in the range of 1.1 to 1.2.

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The crystallization device is a vessel of the same type as that described in connection with the first method. To the addition the solution is to use a pump with adjustable power, to which a program mechanism is switched on, to organize an addition of the solution with a speed which is varied in accordance with the desired program.

The table below gives values from a crystallization carried out at.

Table 2

Volume of the crystallizer ^ O nr Mixture 29 v? = 42.9 to = 59.5 to dry matter Size of the crystals obtained 100yum to 500yum, duration 200 hours

Amount of crystals recovered 19 to = 48 % of the weight of the

pructose contained in the original solution

As seed crystals in the crystallization according to the invention, a mixture of crystals taken from a suitable stage can be used prior crystallization. Aks seed crystals can be used, for example, the crystal mixture that is produced after the Centrifugation remains in the process of this invention.

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Where tons, sometimes abbreviated as "to" above, are used in the description and claims of the present request, metric tons are meant.

Where the crystal size of the fructose in the description above or as stated in the appended claims, the crystal size was obtained from dry samples and from the final product determined by means of the sieve tests (Sceen / Grist Tests) carried out by the International Committee on Uniform Procedures of Analyzes of sugar (International Commission for Uniform Methods of Sugar Analysis) have been tentatively adopted as the standard method for determining the size of sugar crystals. This The method is described on pages 94, 95 and 96 in De Wahlley (Ed) ICUMSA Methods of Sugar Analysis, Elsevier, New York, 1964.

During the crystallization processes, the crystal size of the crystals in the syrup was determined by microscopic observation.

As used herein and in the appended claims, the term "supersaturation" is by means of the formula of Glaasen and Holven (Honig.P .: Principles of sugar technology Vol. II, Slaevler, New York, 1959, pp. 2 ^ 2) as "oversaturation factor" (siiper ^ aturation coefficient) by the following Formula is expressed:

(- ^ i—)

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S / V = sugar / water proportion of a solution with the Purity P and temperature T.

S ₁ ZV ₁ = sugar / water proportion of a saturated solution with purity P and temperature T.

(Sugar = pructose)

Continuous crystallization can be done in a crystallizer which is similar to that used in the single set crystallization. However, it is preferable to use im continuous crystallization process divide the crystallizer into compartments by walls and each compartment with one to equip a separate device for temperature control and for adding the pructose solution. In the distributor walls there are holes through which the mixture flows continuously from compartment to compartment. Each compartment can also be a separate one Be device, in which case the mixture flows from one crystallizer to another. The crystallizers can do the same large or of different sizes.

A typical continuous crystallizer is shown in FIG shown and works as follows:

From a feed tank equipped with a stirrer a mixture of seed crystals is continuously suspended in a saturated fructose solution

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fed to the first compartment of the crystallizer. At the same time a fructose solution, whose temperature with respect to the Pructose is so high that it is saturated or somewhat unsaturated, continuously at a controlled rate fed to the first compartment of the crystallizer. In this compartment the mixture is cooled to a certain temperature so that the crystals grow at a maximum rate without significant formation of new crystals.

Similar pructose solution is added to the mixture that has flowed into the second compartment at a controlled rate and the temperature is lowered again in the same way as in the first compartment. Seed crystals are neither in this compartment nor added in the following compartments.

The number of consecutive compartments can vary, and the functional area of each compartment depends on the number ^ and the size of the compartments. The characteristic digits of the operation of a continuous crystallizer, divided into five compartments, The duration is the same for each level, e.g. 40 - 45 Hours are given in panel j5 below. The output of this crystallizer is around 75 kg / h of fructose crystals.

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ro

Plate 3
Continuous crystallizer

ro
ο step I. II III IV V 9838 Volume no 0.3 0.75 1.5 2.8 5.0 / 0748 Seed crystals (100 / im)
kg / h
Pructose solution
(92 % dry matter) l / h 0.9
6th 10 18th 29 50 Crystal growth / um 100-> l80 180- ^ 240 240- »320 320- ^ 380 380-> 440 Temperature change ⁰ C 50 ^ 45 45 ^> 40 4O-> 35 35- »30 30-J-25 Cooling surface m ² 1.3 2.0 3.0 5.5 11

«Λ

O 3

Ό Q

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ST ω

IS) O CD Ni

Claims (1)

Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz 3 - 21 - Expectations : 1. Process for the crystallization of fructose from its water solution, which includes the following levels: (a) Providing a water-containing fructose solution which contains at least around 90 % dry matter, in that the fructose content of the dry matter is at least around 90% by weight, (b) Bringing the water-containing fructose solution to a temperature at which it is saturated with respect to pructose, (c) adding pructose seed crystals to the solution, (d) lowering the temperature of the resulting mixture at a controlled rate so that the mixture is related becomes saturated on pructose and that an enlargement of the crystal size is caused without any substantial formation of new crystals arrives, and (e) Separating the pructose crystals from the mixture if the crystal size is in the range of around 200 to 500yum, 2. The method of claim 1, wherein the mixture of step (d) is in a state of supersaturation in the range of 1.1 to 1.2 is kept with respect to fructose. 209838/0748 Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz - 22 - 5. The method of claim 1, wherein after the formation of a substantial amount of crystals in the crystallization step (d) a further amount of the water-containing pructose solution Step (a) is added by controlling the temperature and the amount of the added solution to obtain a solution that is saturated with pructose, a second crystallization stage is carried out so that the temperature of the mixture again with a controlled The speed is reduced by the size of the pructose crystals in it without any substantial formation of new fructose crystals to enlarge, and in which the pructose crystals are separated from the mixture when the crystal size is im Range is located around 200 to 500 µm. 4. The method according to claim 3 »in which in step (d) and in the subsequent second crystallization the mixture in a state of supersaturation of 1.1 to 1.2 with respect to pructose is held. 5. The method according to claim j5, characterized in that the Crystallization is carried out as at least two stages, with a separate crystallization device being used for each stage and the volume of the mixture increasing from stage to stage. 6. The method of claim 3, in which a crystal amount of k 5 to 55 # by weight of the dry matter amount of the solution in step (d) is achieved before an amount of fresh solution 209838/0748 Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz 3 is added, the temperature of which is such that they together forms a mixture with the mixture in which the mixture is approximately in the state of saturation with respect to fructose is. 7. The method according to claim 1, characterized in that the temperature of the mixture in step (d) in a crystallizer is controlled so that optimal conditions for the growth of the original seed crystals without substantial formation are brought about by new crystals and, by keeping this temperature unchanged, that fresh solution the same temperature or a higher temperature than that of the mixture to mix with a controlled, increasing Speed is added, what speed of crystallization speed corresponds to until the crystallizer is filled, with reference to the supersaturation of the mixture on fructose is kept in the 1.1 to 1.2 range. 8. The method according to claim 7 * in which after the step of adding of fructose solution the temperature of the mixture is lowered with such a controlled rate that the supersaturation with respect to pructose is kept in the range of 1.1 to 1.2. 9. The method according to claims 1 and 3, characterized in that a crystal mixture, which consists of a stage of a preceding Crystallization has been taken as Samerikristal-Ie is used. 209838/0748 Andrejewski, Honke & Gesthuysen, patent attorneys, 4300 Essen, Theaterplatz 3 10. The method according to claims 1 and J5, characterized in that that during crystallization, dry warm air is blown onto the surface of the mixture to evaporate water will. .•1. The method of claim 1 in which the method is in a running continuously. 12. The method according to claims 1 and 3 * in which the water-containing pructose solution contains from around 2 % to around 4 % of the weight of the solid sugars of an organic solvent that has a low molecular weight and has been selected from the group of methanol, ethanol and isopropanol whereby the rate of crystallization of the pructose is increased. 209838/0748