PROCESS FOR PRODUCING 1,1-GPM- AND/OR 1,6-GPS-ENRICHED ISOMALT COMPOSITIONS

Abstract

The present invention relates to a method for producing 1-O-a-D-glucopyranosyl-D-mannitol- (hereinafter referred to as 1,1-GPM) and/or 6-O-a-D-glucopyranosyl-D-sorbitol- (hereinafter referred to as 1,6-GPS) enriched isomalt compositions from isomalt-containing solutions, i.e. solutions containing hydrogenated isomaltulose, 1,1-GPM- and/or 1,6-GPS-enriched isomalt compositions from isomalt-containing solutions produced by the method according to the invention, as well as the use of these 1,1-GPM- and/or 1,6-GPS-enriched isomalt compositions.

Claims

1. A method for producing 1,1-GPM- and/or 1,6-GPS-enriched isomalt compositions from an isomalt-containing solution, characterised in that a) an isomalt-containing solution is provided, wherein the isomalt-containing solution has 65 to 90 wt. % isomalt (based on the total weight of the isomalt-containing solution); b) the isomalt-containing solution provided in method step a) is subjected to flash evaporation in a reactor for crystal nucleation to obtain a first isomalt-containing suspension comprising a first crystalline phase and a first liquid phase; c) the first isomalt-containing suspension obtained in method step b) is subjected to a crystallisation process whereby a second isomalt-containing suspension comprising a second crystalline phase and a second liquid phase is obtained, wherein the second crystalline phase is 1,1-GPM-enriched and the second liquid phase is 1,6-GPS-enriched; d) the 1,1-GPM-enriched second crystalline phase of the second isomalt-containing suspension of method step c) is separated from the 1,6-GPS-enriched second liquid phase; and e) 1,1-GPM- and/or 1,6-GPS-enriched isomalt compositions are obtained.

2. The method according to claim 1, wherein mechanical agitation is carried out during method step b).

3. The method according to claim 1, wherein the isomalt-containing solution provided in method step a) has 35 to 61 wt. % 1,1-GPM (based on the total weight of the dry matter (DM) of the isomalt-containing solution provided).

4. The method according to claim 1, wherein the isomalt-containing solution provided in method step a) is adjusted to a temperature of 50 to 90? C.

5. The method according to claim 1, wherein the isomalt-containing solution provided in method step a) has 1,1-GPM, 1,6-GPS and at least one compound selected from the group consisting of 1,1-GPS, further deoxy-disaccharide alcohols selected from the group consisting of 1,1-GPS, other deoxy-disaccharide alcohols, polysaccharides, oligosaccharides, trisaccharides, disaccharides, monosaccharides, sorbitol, mannitol and isomelezitose.

6. The method according to claim 1, wherein the isomalt-containing solution provided in method step a) is obtained in method step a1) from an isomalt-containing initial solution or suspension by evaporation or reverse osmosis.

7. The method according to claim 1, wherein the isomalt-containing solution used for method step a1) is obtained by selective hydrogenation, in particular 1,6-GPS-selective hydrogenation.

8. The method according to claim 1, wherein the reactor used for flash evaporation in method step b) is a nucleator.

9. The method according to claim 1, wherein the flash evaporation carried out in method step b) is carried out at an absolute pressure of 10 to 500 mbar, in particular 50 to 200 mbar, and a temperature of 30 to 70? C., in particular 30 to 60? C.

10. The method according to claim 1, wherein the flash evaporation carried out in method step b) is carried out over a period of from 2 minutes to 12 hours.

11. The method according to claim 1, wherein the flash evaporation carried out in method step b) is carried out continuously.

12. The method according to claim 1, wherein method step b) is carried out such that during method step b) 20 to 30% of the dissolved 1,1-GPM present in method step a) passes into the first crystalline phase of the first crystalline isomalt-containing suspension (based on the total weight of the dry matter (DM) of 1,1-GPM in the solution provided in method step a)).

13. The method according to claim 1, wherein method step b) is carried out such that during method step b) the dry matter content of the isomalt-containing solution provided in method step a) is increased by 1 to 6 wt. % (each based on the total weight of the dry matter (DM) of the isomalt-containing solution provided and the first isomalt-containing suspension obtained).

14. The method according to claim 1, wherein the crystallisation process according to method step c) is carried out in a crystalliser.

15. The method according to claim 1, wherein the crystallisation process according to method step c) is carried out continuously.

16. The method according to claim 1, wherein the crystallisation process according to method step c) is an isothermal crystallisation, in particular at a temperature of 50 to 60? C.

17. The method according to claim 1, wherein the crystallisation process according to method step c) is a cooling crystallisation.

18. The method according to claim 1, wherein the crystallisation process according to method step c) is an evaporation crystallisation, in particular a multi-stage evaporation crystallisation.

19. The method according to claim 1, wherein no inoculation with seed crystals is carried out during the method, in particular during the isothermal crystallisation in method step c).

20. The method according to claim 1, wherein after method step d) the 1,1-GPM-enriched second crystalline phase is dried and in method step e) a solid 1,1-GPM-enriched isomalt composition is obtained.

21. The method according to claim 1, wherein after method step d) the 1,6-GPS-enriched second liquid phase is concentrated at least once, in particular concentrated to at least 60 wt. % dry matter content (based on the total weight of the second liquid phase), and in method step e) a liquid 1,6-GPS-enriched isomalt composition is obtained.

22. The method according to claim 1, wherein after method step d) the 1,6-GPS-enriched second liquid phase is dried, and in method step e) a solid 1,6-GPS-enriched isomalt composition is obtained.

23. The method according to claim 1, wherein the second crystalline phase separated in method step d) has at least 60 wt. % 1,1-GPM (based on the total weight of the dry matter (DM) of the crystalline phase).

24. The method according to claim 1, wherein the second liquid phase separated in method step d) has at least 72 wt. % 1,6-GPM (based on the total weight of the dry matter (DM) of the second liquid phase).

25. A 1,1-GPM-enriched isomalt composition, in particular producible by a method according to claim 1, wherein the 1,1-GPM-enriched isomalt composition has a length-to-width ratio of the crystals contained therein of from 7.0 to 10.5, in particular from 7.5 to 10.0, in particular from 7.5 to 9.0, in particular from 7.5 to 8.5, in particular from 8.0 (each mean value).

26. A 1,6-GPS-enriched isomalt composition having 15 to 32 wt. % 1,1-GPM and 68 to 85 wt. % 1,6 GPS (each based on the dry matter of the total amount of 1, 1-GPM and 1,6-GPS), in particular producible by a method according to claim 1, in particular having a 1,6-GPS-content of at least 68 wt. % (based on the total weight of the dry matter (DM) of the composition).

27. Use of a 1,1-GPM- and/or 1,6-GPS-enriched isomalt composition produced by a method and/or composition according to claim 1, in products for human and/or animal consumption.

Description

[0250] The figures show:

[0251] FIG. 1: Solubility diagram according to Schiweck (H. Schiweck, alimenta 19, Palatinit?-Herstellung, technologische Eigenschaften und Analytik palatinithalthaltiger Lebensmittel, 5-16, 1980) for 1,1-GPM (GPM, 3), 1,6-GPS (GPS, 2) and isomalt (Isomalt, 1) in water, in which the solubility limits of the above-mentioned components are shown as a function of temperature,

[0252] FIG. 2A to 2D: Microscopic images of crystallisation products from example 2.1 (magnification ?4),

[0253] FIG. 3A to 3D: Microscopic images of crystallisation products from example 2.1 (magnification ?10),

[0254] FIG. 4A to 4D: Microscopic images of crystallisation products from example 2.2 (magnification ?10 and ?20),

[0255] FIG. 5A to 5F: Microscopic images of crystallisation products from example 2.3 (magnification ?4 and ?10),

[0256] FIG. 6A to 6F: Microscopic images of crystallisation products from example 2.4 (magnification ?4 and ?10),

EXAMPLE 1

[0257] Separation of isomalt (hydrogenated isomaltulose) into 1,1-GPM- and 1,6-GPS-enriched isomalt compositions by flash evaporation in method step b) and subsequent isothermal crystallisation in method step c).

[0258] The two main components of isomalt, i.e., 1,1-GPM and 1,6-GPS, have different solubility products in aqueous solutions (FIG. 1). In suspension, each component forms its own solubility equilibrium. The more easily crystallising or poorly soluble component 1,1-GPM accumulates in the solid part of the suspension (crystalline phase), since the less easily crystallising or more soluble component 1,6-GPS preferentially goes into solution or remains in solution. The equilibria that form are temperature-dependent for the same concentration of isomalt in water in the suspension. At the same temperature, the proportion of 1,6-GPS in the solution increases as the proportion of the dry matter (DM) in the suspension increases. The solubility diagram of 1,1-GPM, 1,6-GPS and isomalt (Figure) shows a steady increase in the solubility of each component with increasing temperature. The present invention makes use of this observation. An isomalt-containing solution obtained by conventional process steps is thermally thickened in a method step a1) to a dry matter content of 70 to 85 wt. %. The isomalt-containing solution thus obtained and provided in method step a) (isomalt content 70 to 85 wt. % based on the total weight of the solution) with a content of 1,1-GPM of 35 to 44 wt. %, namely 40.7 wt. %, and a content of 1,6-GPS of 56 to 65 wt. %, namely 58.4 wt. %, 0.01 to 2 wt. % GPI, 0.01 to 2 wt. % glycosylglycitols, 0.01 to 0.4 wt. % sorbitol, 0.001 to 2 wt. % deoxy-disaccharide alcohols, 0.1 to 10 wt. % 1,1-GPS and/or 0.01 to 0.3 wt. % mannitol (each based on the total weight of the dry matter of the isomalt-containing solution) is then brought to a temperature of 60 to 75? C. and then subjected to flash evaporation according to method step b) of the method according to the invention for crystal nucleation in the so-called nucleator. After adjusting the temperature of the isomalt-containing solution to 60 to 75? C., the flash evaporation is operated at an absolute pressure of 50 to 200 mbar, in particular 90 to 100 mbar, and at a temperature of 50 to 55? C. Due to the reduced absolute pressure, the vapour pressure increases and the induced energy dissipation causes the 1,1-GPM, which is less soluble in water than 1,6-GPS (see solubility according to Schiweck, FIG. 1), to change into a crystalline first phase according to its thermodynamic solubility product (initially about 5% of the 1,1-GPM present in the initial solution). Due to the agitator geometry used in the reactor and the shear forces thus continuously generated, further 1,1-GPM-enriched crystal nuclei are continuously formed.

[0259] After a residence time of up to 5 h, about 25 wt. % of the 1,1-GPM initially present in the initial solution has passed into the first crystalline phase, wherein the first liquid phase obtained after carrying out the nucleation process according to method step b) has 31 wt. % 1,1-GPM and 68 wt. % 1,6-GPS (based on the total weight of the dry matter in solution). The first isomalt-containing suspension obtained from method step b), comprising 1,1-GPM-enriched crystal nuclei obtained by method step b), is continuously subjected to a crystallisation process according to method step c), carried out in a temperature-controlled crystalliser. In this process, the 1,1-GPM-enriched crystal nuclei continue to grow into crystals under isothermal conditions in a temperature range of 50 to 60? C., in particular 56? C., until the residual supersaturation has largely dissipated. The obtaining of isothermal conditions is ensured by the continuous removal of the released crystallisation energy. By slowly lowering the temperature of the ripening container (crystalliser) step by step (at most 0.5 K/h, in particular at most 0.1 K/h) to 55? C., the yield of 1,1-GPM-enriched crystals is additionally increased without negatively affecting the purity of these crystals. The second suspension thus obtained can be worked up by means of suitable separation techniques according to method step d) (for example centrifugation), wherein the second crystalline phase thus obtained contains 69.9 wt. % 1,1-GPM and 29.8 wt. % 1,6-GPS (based on the total weight of the dry matter of the second crystalline phase) and the separated second liquid phase contains 20.2 wt. % 1,1-GPM and 78.6 wt. % 1,6-GPS (based on the total weight of the dry matter of the second liquid phase).

EXAMPLE 2

[0260] In the following example, the method according to the invention (Example 2.1) is compared with known crystallisation methods (Examples 2.2 to 2.4).

[0261] The experiments were carried out in a 2-litre cooling crystalliser. This is equipped with an agitator and a double jacket for heating by means of a thermostat. The separation of crystal magmas took place in a heated pressure Nutche or in a pilot plant centrifuge. A microscope was used for image documentation of the crystals in the crystal suspensions. The Olympus Stream Motion software was used for image analysis.

[0262] The enriched phases obtained from the experiments were analysed as follows: [0263] Analysis of the water content of the filter cake (second crystalline phase) using the Karl Fischer method. [0264] analysis of the water content of the filtrate (second liquid phase) by refractometry [0265] Analysis of the 1,1-GPM-content and 1,6-GPS-content by HPLC [0266] Analysis of the length-to-width ratio:

[0267] Using an Olympus camera (Olympus UC 90) and associated Olympus software and a Zeiss microscope (Carl Zeiss Axiolab re), microscopic crystal images were taken of the glycerol-dispersed second isomalt-containing suspension (Magma) at magnifications of 4? and 10?. At least twenty individual crystals per crystal image, selected by means of a random generator, were measured with regard to crystal length and crystal width using the image analysis software Olympus Stream Motion (maximum characteristic crystal length and, in addition, the maximum characteristic crystal width at a 90? angle) and the ratio of measured length to measured width was determined by calculation and the mean or median value was determined from this. Preferably, a diagonal line laid through the microscopic crystal photo (crystal image) is used as a random generator and all crystals on this diagonal line allowing a clear distinction and determination of the crystal length and width are used for the determination of the length-to-width ratio, wherein at least twenty crystals must be recognisable on the line. Otherwise, another microscopic image was taken and used.

[0268] In the following Table 1, the 1,1-GPM- and 1,6-GPS-contents of the isomalt solutions used in this example are given in relation to DM (dry matter) and total mass of the isomalt solution).

TABLE-US-00001 TABLE 1 Analysis of the initial isomalt solutions 1,1-GPM- 1,6-GPS- 1,1-GPM- 1,6-GPS- content in content in content in content in g/100 gDS g/100 gDS g/100 g g/100 g Example 2-1 40.40 57.39 31.4 44.6 Example 2-2 46.08 51.39 22.6 25.2 Example 2-3 46.63 51.00 36.2 39.6 Example 2-4 46.66 51.30 36.2 39.8

Example 2.1 (According to the Invention)

[0269] A second suspension (magma) obtained according to the teaching of example 1 is partially removed from the crystallizer before centrifugation according to method step d), diluted in glycerol and crystal images are recorded. Further, a separation according to method step d) of the solid from the liquid phase is carried out in a centrifuge at a speed of 1800 revolutions per minute for 30 minutes:

[0270] FIGS. 2A to 2D show crystal images of the obtained magma dispersed in glycerol, magnification ?4, and FIGS. 3A to 3D show crystal images of the obtained magma dispersed in glycerol, magnification ?10.

[0271] The length-to-width ratio of the crystals obtained in the magma and in the second crystalline phase obtained in method step d) were 8.0 (mean) and 7.8 (median).

[0272] Table 2 below shows the composition of the phases obtained after separation (filter cake is the solid crystalline phase, filtrate is the liquid phase).

TABLE-US-00002 TABLE 2 Analysis of the enriched phases, each based on total mass Filter cake filtrate Water content in g/100 g 16.1 25.9 1,1-GPM-content in g/100 g 55.2 15.3 1,6-GPS-content in g/100 g 29.4 56.8 Ratio of 1,1-GPM to 1,6-GPS in g/g 1.88 0.27 1,1-GPM-content in g/100 gDS 65.8 20.6 1,6-GPS-content in g/100 gDS 35.0 76.6

[0273] The obtained crystals in the solid phase are particularly pure and show a high uniformity in shape and size. The crystal suspension after completion of crystallisation shows no fine grain formation in the crystal image. The length-to-width ratio of the crystals contained in the second crystalline phase obtained in method step d) is comparatively small. The separation of the obtained second crystalline phase by centrifugation was took place without problems in a very satisfactory manner, which is particularly shown in the enrichment of 1,1-GPM in the crystalline phase after centrifugation. The 1,6-GPS-enriched filtrate, i.e., the 1,6-GPS-enriched second liquid phase, drains very well from the filter cake. According to the invention, an enrichment of 1,1-GPM and a depletion of 1,6-GPS are found in the obtained second crystalline phase, while similarly, an enrichment of 1,6-GPS and a depletion of 1,1-GPM are found in the obtained second liquid 1,6-GPS-enriched phase, each compared to the starting composition.

Example 2.2 (not According to the Invention)

[0274] WO 1997/008958 A1 discloses methods for producing 1,6-GPS-enriched and 1,1-GPM-enriched mixtures. Example 2 of this document discloses the preparation of 1,1-GPM and 1,6-GPS-enriched 1,1-GPM/1,6-GPS mixtures, wherein IsomaltR is added to 5 kg of water (fully demineralised) and the obtained suspension is stirred at 35? C. for 1-20 hours depending on the particle size. Subsequently, this suspension is separated into a liquid phase and solid phase at 35? C. in a heated pressure Nutsche.

Experimental Procedure:

[0275] 1. switch on the thermostat for heating the 2-litre crystalliser adjust the flow temperature to 35.3? C. Temperature control via the internal temperature sensor of the thermostat. [0276] 2. add 999.79 g of demineralised water to the 2-litre crystalliser [0277] 3. switch on the stirrer and adjust the speed to 60 rpm [0278] 4. preheat the water to 35? C. [0279] 5. add 999.96 g Isomalt ST-M to the 2-litre crystalliser [0280] 6. 19.5 hours after addition of the Isomalt: Preheat the double-jacket pressure Nutsche to 35? C. via thermostat [0281] 7. 20 hours after addition of the isomalt: Removal of the obtained crystal suspension (magma) from the crystalliser [0282] 8. produce a dilution of part of the magma with demineralised water (one to one) for analysis [0283] 9. disperse a part of the magma in glycerine for recording crystal images in the suspension [0284] 10. transfer 200 ml of magma into the preheated pressure Nutsche and separate the crystal from the mother solution. A filter fleece made of polyethylene of the company Porvair Sciences type Vyon D with a mesh size of 15-25 ?m is used as a filter. [0285] 11. dilution of the collected filtrate with demineralised water (one to one) for analysis [0286] 12. removal of crystals from the pressure Nutsche for analysis Experimental results:

[0287] According to example 2 of WO 1997/008958 A1, no isomalt-containing solution but a suspension of isomalt in water is used as starting material for the desired enrichments and subsequent separation of the enriched solid and liquid phases. Therefore, no crystallisation of isomalt components from a solution takes place in this method during the incubation at 35? C. for about 20 hours, but only a partial solving and dissolving of undissolved isomalt components from the solid phase of the suspension into the liquid phase and vice versa.

[0288] FIGS. 4A and 4B show images of the obtained magma dispersed in glycerol, magnification ?10, and FIGS. 4C and 4D show images of the obtained magma dispersed in glycerol, magnification ?20.

[0289] Despite the chosen high-resolution magnification, no single crystals are visible, but only partially dissolved, flake-like particles, which is due to the partially amorphous solidified structure of the isomalt particles used in the initial suspension, which represent conglomerates of small crystallites of 1,1-GPM and 1,6-GPS. These do not originate from a crystallisation process but from a drying process and consequently do not show any crystal forms to be expected in a classical crystallisation. The principle of enrichment realised in this comparative example is based on a release of the more soluble 1,6-GPS component from a solid containing 1,1-GPM and 1,6-GPS 20 and thus does not correspond to an enrichment according to the invention by crystallisation from a solution containing 1,1-GPM and 1,6-GPS.

[0290] Table 3 below shows the 1,1-GPM- and 1,6-GPS-contents of the phases obtained after separation.

TABLE-US-00003 TABLE 3 Analysis of the enriched phases (filter cake is the solid crystalline phase, filtrate is the liquid phase), each based on total mass Filter cake filtrate Water content in g/100 g 21.2 55.4 1,1-GPM-content in g/100 g 69.0 15.1 1,6-GPS-content in g/100 g 9.6 28.0 Ratio of 1,1-GPM to 1,6-GPS in g/g 7.22 0.54 1,1-GPM-content in g/100 gDS 87.6 33.9 1,6-GPS-content in g/100 gDS 12.1 62.8

Example 2.3 (not According to the Invention)

[0291] EP 0859 006 B2 discloses methods for producing 1,6-GPS-enriched and 1,1-GPM-enriched mixtures. Example 1 of this document discloses the production of 1,1-GPM and 1,6-GPS-enriched 1,1-GPM/1,6-GPS mixtures using a seeding step and two different cooling rates during crystallisation.

Experimental Procedure:

[0292] 1. switch on the thermostat to heat the 2-litre crystalliser and adjust the feed temperature to 85? C. [0293] 2. add 649.91 g demineralised water to the 2-litre crystalliser [0294] 3. switch on the stirrer and adjust the speed to 100 rpm [0295] 4. heat the water to 85? C. [0296] 5. add 2453.2 g Isomalt ST-F to the 2-litre crystalliser [0297] 6. start the cooling program [0298] a. Maintain 85? C. for 2 hourstemperature control via external PT100 in the crystalliserstirrer speed 100 rpm [0299] b. cool 85? C. to 65? C. for 2 hourstemperature control via internal PT100 in the thermostatstirrer speed 60 rpm [0300] c. cool 65? C. to 37? C. over 23.3 hourstemperature control via internal PT100 in thermostatstirrer speed 60 rpm [0301] 7. after reaching 62? C.: add 0.5 g Isomalt ST-PF in 4.95 g isopropanol to the solution via a syringe [0302] 8. after reaching 37? C.: removal of the magma from the crystalliser [0303] 9. produce a dilution of part of the magma with demineralised water (one to one) for analysis [0304] 10. disperse a part of the magma in glycerine to record crystal images in the suspension [0305] 11. transfer 604 g of magma into a centrifuge and separate the crystal and mother solution. The sieve used is a filter fleece made of polyethylene from Porvair Sciences type Vyon D with a mesh size of 15-25 ?m. Speed is 1800 revolutions per minute. Centrifugation time 30 minutes. No water cover. [0306] 12. dilution of the collected outlet with demineralised water (one to one) for analysis [0307] 13. removal of the crystals from the centrifuge

[0308] Separation in the centrifuge could not be carried out satisfactorily. The mass of outlet was low. The filter cake had a visually clearly recognisable high residual moisture.

[0309] FIGS. 5A, 5B and 5C show crystal images, magma dispersed in glycerol, magnification ?4, and FIGS. 5D, 5E and 5F crystal images, magma dispersed in glycerol, magnification ?10.

[0310] The length-to-width ratio of the crystals in the magma 11.2 (mean) and 11.1 (median).

[0311] Table 4 below shows the 1,1-GPM- and 1,6-GPS-contents of the phases obtained after separation.

TABLE-US-00004 TABLE 4 Analysis of the enriched phases (filter cake is the solid crystalline phase, filtrate is the liquid phase), each based on total mass Filter cake filtrate Water content in g/100 g 19.0 30.2 1,1-GPM-content in g/100 g 42.9 11.3 1,6-GPS- content in g/100 g 35.6 56.0 Ratio of 1,1-GPM to 1,6-GPS in g/g 1.21 0.20 1,1-GPM- content in g/100 gDS 53.0 16.3 1,6-GPS- content in g/100 gDS 44.0 80.3

[0312] The crystal images clearly show that significant fine grain formation occurs in the crystal suspension after completion of crystallisation. The length-to-width ratio of the crystals is relatively large. Separation of the crystalline phase by centrifugation is not satisfactory. The enrichment of 1,1-GPM in the obtained crystalline phase after centrifugation is minimal and the contents of 1,1-GPM and 1,6-GPS in the filter cake correspond approximately to the composition of the initial solution. The 1,6-GPS-enriched filtrate drains very poorly from the filter cake.

Example 2.4 (not According to the Invention)

[0313] U.S. Pat. No. 6,414,138 B1 also discloses methods for producing 1,6-GPS-enriched and 1,1-GPM-enriched mixtures. Example 1 of this document discloses the production of 1,1-GPM and 1,6-GPS-enriched 1,1-GPM/1,6-GPS mixture so as described in Example 2.3, but using two different cooling rates during crystallisation without seeding.

Experimental Procedure:

[0314] 1. switch on the thermostat to heat the 2-litre crystalliser and adjust the feed temperature to 85? C. [0315] 2. add 627.44 g demineralised water to the 2-litre crystalliser [0316] 3. switch on the stirrer and adjust the speed to 100 rpm [0317] 4. heat the water to 85? C. [0318] 5. add 2372.5 g Isomalt ST-F to the 2-litre crystalliser [0319] 6. start the cooling programme [0320] a. Maintain 85? C. for 2 hourstemperature control via external PT100 in the crystalliserstirrer speed 100 rpm [0321] b. cool 85? C. to 65? for 2 hourstemperature control via internal PT100 in the thermostatstirrer speed 60 rpm [0322] c. cool 65? C. to 37? C. g over 23.3 hourstemperature control via internal PT100 in thermostatstirrer speed 60 rpm [0323] 7. after reaching 37? C.: removal of the magma from the crystalliser [0324] 8. produce a dilution of part of the magma with demineralised water (one to one) for analysis [0325] 9. disperse a part of the magma in glycerine to record crystal images in the suspension

[0326] FIGS. 6A, 6B and 6C show crystal images, magma dispersed in glycerol, magnification ?4 and FIGS. 6D, 6E and 6F show crystal images, magma dispersed in glycerol, magnification ?10.

[0327] The length-to-width ratio of the crystals in the magma was 11.3 (mean) and 10.5 (median).

[0328] These crystal images also clearly show that significant fine grain formation occurs in the crystal suspension after completion of crystallisation. The length-to-width ratio of the crystals is relatively large and comparable to that of Example 2.3.