METHOD AND DEVICE FOR THE DIGESTION OF STARCH

Abstract

With a method for digesting starch, an aqueous slurry of the starch is treated with steam in a cooking vessel and in this case exposed to shear forces, wherein the starch-containing slurry is heated to a temperature of between 85□C and 110□C in the cooking vessel by introducing steam, and the digestion step is implemented until the desired degree of digestion has been reached. Also described is a cooking vessel that can be used when the method for digesting starch is being carried out.

Claims

1. Method for digesting starch, comprising: a) Creating an aqueous slurry of powdery starch, b) Introducing the slurry into a cooking vessel (4), c) Treating the slurry in the cooking vessel (4) with steam, wherein the slurry is exposed by mechanical action to shear forces that are created by a rotor with a finned dispersing disk, and wherein steam is fed from a hollow ring (70), arranged below the rotor, in which openings directed toward the rotor (42) are provided for the discharge of steam, in order to implement thermomechanical digestion, and d) Drawing off the starch, converted at least partially into paste, from the cooking vessel(4.

2. The method according to claim 1, wherein steam exits from a hollow displacement element (60), which is arranged in the cooking vessel (4), through at least one outlet opening (63) for steam in the area of the rotor (42).

3. The method according to claim 1, wherein the starch-containing slurry is heated to a temperature of between 85° C. and 135° C. in the cooking vessel (4) in step c) by introducing steam.

4. The method according to claim 1, wherein step c) is implemented during a time span of 1 to 5 hours.

5. The method according to claim 1, wherein in step a), a slurry with at most 35-45% starch powder is created as a solid.

6. The method according to claim 1, wherein the slurry is heated before step b) to a temperature of between 85° C. and 95° C.

7-10. (canceled)

11. The method according to claim 1, wherein when implementing step c), the degree of digestion of starch is set by selecting the speed at which the slurry is stirred in the cooking vessel.

12. The method according to claim 1, wherein when implementing step c), the degree of digestion of starch is set by selecting the throughput of the slurry.

13. The method according to claim 1, wherein when implementing step c), the degree of digestion of starch is set by selecting the temperature of the slurry.

14-16. (canceled)

17. The method according to claim 1, wherein the throughput of slurry through the cooking vessel (4) is regulated in step c) by obstructing the flow of slurry through the cooking vessel (4) and/or by static mixing of the slurry in or behind the cooking vessel (4).

18. The method according to claim 1, wherein in step a), cationic starch powder is used in order to create the slurry.

19. The method according to claim 1, wherein in step a), native starch powder is used in order to create the slurry.

20. Device in the form of a cooking vessel (4) for implementing step c) of the method according to claim 1, with a container (40), a cover (41), a line (50), emptying into the cover, for the slurry; a line, provided in the cover (41), for draining at least partially converted starch (paste); stator sheets (61) provided in the interior of the container (40) and designed as baffles; a rotor (42), and an annular displacement element (60), whose outside surface is some distance from the inside surface of the container (40) and whose inner opening is arranged coaxially to the rotor (42), the device comprising a steam feed line (62), which empties into the interior of the container (40).

21. The device according to claim 20, wherein the steam feed line (62) empties into the hollow displacement element (60) and wherein the displacement element (60) has at least one outlet opening (63) for steam on a side that is opposite to the emptying point of the line (62) and adjacent to the rotor (42).

22. The device according to claim 21, wherein the outlet openings (63) are provided in a distributed manner over the annular end surface, facing the rotor (42), of the displacement element (60).

23. The device according to claim 20, wherein the steam feed line (62) empties into a hollow ring (70) with at least one outlet opening for steam.

24. The device according to claim 23, wherein the ring (70) is arranged on the side of the rotor (42) that turns away from the displacement element (60).

25. The device according to claim 23, wherein the outlet opening is provided in the wall of the ring (70) that faces the rotor (42).

26. The device according to claim 23, wherein the ring (70) has multiple outlet openings that are arranged in a distributed manner over the ring's extension.

27. The device according to claim 20, wherein the stator sheets (61) protrude from the displacement element (60) and project to the inside surface of the container (40).

28. The device according to claim 20, wherein the rotor (42) has fins (45) at least on one side.

29. The device according to claim 20, wherein the opening of the displacement element (60) that is coaxial to the shaft of the rotor (42) is funnel-shaped, wherein the broadened area of the opening faces toward the cover (41) of the container (40).

30. The device according to claim 20, wherein the axis of the line (50) is oriented coaxial with the annular displacement element (60) and with the rotor (42).

31. The device according to claim 20, wherein the fins (45) on the dispersing disk (44) increase in height from the inside to the outside.

32. The device according to claim 20, wherein the fins (45) are set obliquely to the radial planes, which pass through the shaft of the rotor (42).

33. The device according to claim 20, wherein the rotor (42) projects through the bottom of the container into the interior of the container (40).

34. The device according to claim 20, wherein in the area of the emptying point of the line (50), a constriction (52) that acts as a diffuser is provided.

35. The device according to claim 20, wherein the constriction (52) is formed by an annular fin.

36. Method according to claim 1, wherein enzyme is added to the paste that is obtained according to step d) and wherein starch that is contained in the paste is broken down under the action of enzyme.

37. Method according to claim 36, wherein the enzyme is deactivated.

38. Method according to claim 37, wherein the deactivation of the enzyme is carried out by heating the paste to a temperature of between 120° C. and 135° C.

39. Method according to claim 38, wherein the temperature is increased by introducing steam.

Description

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] Additional details and features of the invention are given in the description below with reference to the drawings, in which known units and procedures, procedures according to the invention and units according to the invention as well as a cooking vessel that can be used according to the invention are depicted by way of example. Here:

[0070] FIG. 1 shows diagrammatically a (known) unit for enzymatic breakdown of native starch,

[0071] FIG. 2 shows diagrammatically a (known) unit for digesting cationic starch,

[0072] FIG. 3 shows a unit for carrying out a (continuous) method for enzymatic breakdown of native starch,

[0073] FIG. 4 shows a unit for implementing the method according to the invention for digesting cationic starch,

[0074] FIG. 5 shows, in a block diagram, a known method for the enzymatic breakdown of starch,

[0075] FIG. 6 shows, in a block diagram, a known method for digesting cationic starch,

[0076] FIG. 7 shows, in a block diagram, a method according to the invention for digesting cationic starch,

[0077] FIG. 8 shows, partially and in section, two embodiments of a cooking vessel, which can be used when implementing the method according to the invention, and

[0078] FIG. 9 shows a unit that is also suitable for implementing the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0079] The known method for starch that is to be broken down enzymatically, which method can be implemented continuously in a unit according to FIG. 1 and according to the block diagram of FIG. 5, can be described as follows:

[0080] Used as raw components are:

[0081] Native starch powder,

[0082] Water,

[0083] Steam, and

[0084] Enzyme (amylase).

[0085] Starch powder is stored in BigBags 1 or silos 2. From this supply, the starch powder is fed into the slurry station 1. In this station 3, the starch powder is introduced into water, and a slurry (suspension) with up to 35% solid content is created. From there, the slurry (starch suspension) is pumped using a pump 5 into a cooking vessel 4. The enzymes can be added in measured quantities from a supply container 6 in the slurry station 3, in front of or behind the pump 5. In most units, before it enters the cooking vessel 4, the slurry is brought to the agglutination temperature (85° C. to 95° C.) by means of steam injection 9.

[0086] In addition, static mixers or other components can be installed in the feed of the cooking vessel 4 in order to prevent the slurry from shooting through and to configure the feed to be homogeneous. In the actual cooking vessel 4, the necessary dwell time (8 to 20 minutes) for the desired degree of breakdown is set by means of volume buffering. In the cooking vessel 4, stirring mechanisms and/or mixer-disks are installed in order to accelerate the breakdown process, by shear forces being brought into the slurry in the cooking vessel 4.

[0087] By means of a pump 7, paste is continuously drawn off from the cooking vessel 4 and pumped through a deactivation zone 8. The deactivation zone 8 is a plug flow reactor, in which the paste is heated to 120° C. to 135° C. at the beginning by means of steam injection 9, wherein the deactivation time can be controlled by the pipe volume and/or the pumping power. After the breakdown process is stopped, the paste that is obtained is optionally diluted with water from a line 15 and then stored.

[0088] It is known to provide a labyrinth pipe instead of the cooking vessel 4 after the steam injection, in which pipe firstly the necessary dwell time can be achieved and secondly, via shear edges, an additional shearing of the slurry is achieved.

[0089] The cooking vessel can—when it is made accordingly large enough—also be used in batch operation. Then, all method steps are run starting from the production of suspension in the cooking vessel 4. The drawback is that relatively large units are necessary or accordingly small throughput amounts can be run.

[0090] With the known method of a cooking process for cationic starch, which can be carried out in a unit according to FIG. 2 and which can flow as indicated in the block diagram of FIG. 7, it is possible to proceed as follows:

[0091] Used as raw components are:

[0092] Cationic starch powder,

[0093] Water, and

[0094] Steam.

[0095] Starch powder is stored in BigBags 1 or silos 2. The slurry station 3 is fed from this supply. In this station 3, the powder is introduced into water, and a slurry (suspension) with up to 15% solid content is created. From there, the starch suspension is pumped into the cooking tube 10.

[0096] The cooking tube 10 is a plug flow reactor, in which the starch suspension is heated to 115° C. to 135° C. at the beginning by means of steam injection 9, wherein the dwell time can be controlled by the pipe volume and/or the pumping power. After the cooking process, the paste that is obtained (digested starch) is optionally diluted again (water from line 15) and then stored.

[0097] It is known to provide a labyrinth pipe instead of the cooking tube 10 after the steam injection 9, in which pipe firstly the necessary dwell time can be achieved and secondly, via shear edges, an additional shearing of the slurry is achieved.

[0098] The cooking tube can be replaced by a cooking vessel 10. When it is made accordingly large enough, the cooking vessel 10 can also be used in batch operation. Then, all method steps are run starting from the production of suspension in the cooking vessel 10. The drawback is that relatively large units are necessary, or accordingly small throughput amounts can be run.

[0099] A method for digesting cationic starch according to the invention can be carried out in a unit, which is shown in FIG. 4 and uses a cooking vessel according to FIG. 8, wherein the method can flow as indicated in the block diagram according to FIG. 7. In detail, in this case, it is possible to proceed as follows:

[0100] Used as raw components are:

[0101] Cationic starch powder,

[0102] Water, and

[0103] Steam.

[0104] Starch powder is stored in BigBags 1 or silos 2. The slurry station 3 is fed from this supply. In this station 3, the powder is introduced into water from the line 11, and a slurry (suspension) with up to 35% solid content is created. From there, the starch suspension is pumped with the pump 5 into the cooker 4.

[0105] The steam injection is carried out via a line 13 directly into the cooker 4, where the slurry is brought to the agglutination temperature (85° C. to 135° C.).

[0106] In addition, static mixers or other components can be installed after the fact, in order to prevent the slurry from shooting through the cooker 4 and/or to configure the cooking process to be more homogeneous. In the cooker 4, the desired starch properties can be set by means of a change in speed, a change in throughput, and/or the cooking temperature.

[0107] The paste that is obtained is optionally diluted with water from the line 15 and then stored.

[0108] A device (cooker 4), which can be used for digesting cationic starch when implementing the method according to the invention, can have the design that is shown in FIG. 8.

[0109] A device according to the invention that is used as the cooking vessel 4 comprises a container 40, which is closed on its top by a cover 41. In the container 40, a rotor 42, which is mounted in a bearing body (not shown) that is arranged below the container 40, projects from below.

[0110] The feedthrough of the rotor 42 into the container 40 is sealed by sliding-ring seals 43.

[0111] The rotor 42 is mounted in the bearing body by roller bearings (not shown).

[0112] In its part that is arranged in the lower area of the container 40, the rotor 42 has a dispersing disk 44, which on its top has fins 45 that are tilted relative to the radial direction. In this case, the orientation of the fins 45 relative to the direction of rotation of the rotor 42 in an embodiment is selected so that the radial inner ends of the fins 45, relative to the direction of rotation, lie further forward than the radial outer ends of the fins.

[0113] In a modified embodiment, the fins 45 are oriented so that their radial outer ends, relative to the direction of rotation, lie further back than their radial inner ends.

[0114] Moreover, the fins 45 can increase in height from the inside to the outside.

[0115] The fins 45 are, for example, curved on the top of the dispersing disk 44. Curved fins 45 are oriented either so that the convex side of the fins 45 points toward the front relative to the direction of rotation of the dispersing disk 44 or so that the convex side points toward the rear relative to the direction of rotation of the dispersing disk 44.

[0116] The fins 45 on the top of the dispersing disk 44 can thus also be curved, so that the concave side of the fins 45 points toward the front or toward the rear relative to the direction of rotation of the dispersing disk 44.

[0117] The fins 45 on the top of the dispersing disk 44 can also be straight fins.

[0118] Because of the rotating rotor 42, which is provided in the cooking vessel 40 (cooker), with the dispersing disk 44, shear forces are brought into the slurry of starch introduced into the container 40, thereby advantageously supporting the digestion of starch.

[0119] The rotor 42 has, for example, a diameter of 100 to 150 mm, preferably 130 mm, and—including the fins 45 on the dispersing disk 44—a height of, for example, 3 to 10 mm, in particular 5 to 7 mm. The rotor 42 is rotated at, for example, a speed of between 3,000 and 5,000 rpm. The speed of the rotor 42 is selected based on its diameter in order to reach the necessary circumferential speed.

[0120] On the rotor 42, a propeller 46 with blades 47 is provided above the dispersing disk 44; in the suspension that is to be prepared, the propeller creates a flow that is directed downward onto the dispersing disk 44. The propeller 46 is not necessarily provided.

[0121] In the cover 41, a line 50, through which the suspension flows into the container 40, empties coaxially to the rotor 42.

[0122] On the inside of the cover 41, a cone-shaped projection 51 that points inward is provided, a projection into whose center the suspension feed line 50 empties.

[0123] This arrangement of the line 50 ensures an optimal mixing of the suspension, which is located in the circuit in the container 40 with suspension that is newly fed into the container 40.

[0124] Because at the end of the line 50 (emptying point in the container 40), there is a constriction 52 acting as a diffuser (formed by an annular fin that is triangular in cross-section), the above-mentioned mixing of the fed suspension with suspension that is already in the container 40 and is being prepared is advantageously supported.

[0125] Drain lines (or at least one) encircling the feed line 50 are provided for draining prepared suspension (digested starch).

[0126] The cover 41 is screwed to the container 40.

[0127] In the inside space of the container 40, an annular displacement element 60 is provided, whose inner opening can be designed approximately funnel-shaped. Between the outside surface of the displacement element 60 and the inside of the wall of the container 40, an annular channel is located, in which suspension flows upward after leaving the dispersing disk 44. Suspension, optionally supported by the propeller 45 on the rotor 42, flows through the inner opening of the displacement element 60 downward in the direction toward the dispersing disk 44.

[0128] In the embodiment that is shown, the upper end of the rotor 42 is covered by an aerodynamically-efficient covering that is fixed in the rotor 42 using a socket screw.

[0129] On the outside of the displacement element 60, stator sheets 61, which span the annular channel (gap) between the outside of the displacement element 60 and the inside of the wall of the container 40 (in particular in its lower part), i.e., with its free edges adjoin the inside of the wall of the container 40, are provided as baffles.

[0130] In order to hold the displacement element 60 in the interior of the container, fastening screws can be provided.

[0131] With the embodiment of the cooking vessel 4 that is shown on the left in FIG. 8, the displacement element 60 is hollow and is fed with steam via a line 62, which is guided through the cover 41 of the housing 40 of the cooking vessel 4. The line 62 empties into the upper end surface of the hollow displacement element 60. On its bottom, the displacement element 60—distributed around the inner opening of the displacement element 60—has multiple outlet openings 63, so that steam that is introduced via the line 62 into the inside space of the displacement element 60 can exit into the inside space of the container 40 in the area of the rotor 42, in particular in the area of its dispersing disk 44.

[0132] In the embodiment that is shown on the right in FIG. 8, a hollow ring 70 (diffuser ring) is provided, in which ring openings are provided for the discharge of steam. As shown on the right in FIG. 9, the ring 70 is arranged on the side of the dispersing disk 44 of the rotor 40 that turns away from the displacement element 60, wherein the outlet openings in the ring 70 are directed upward, i.e., in the direction toward the displacement element 40. For the sake of clarity, the line via which steam is fed to the ring 70 is not depicted in FIG. 9.

[0133] For certain applications, it can be advantageous for the feeding of steam into the inside space of the container 40 of the cooking vessel 4 to be carried out both via the hollow displacement element 60 and via the ring 70.

[0134] In the case of the unit for starch preparation (digestion of starch) shown in FIG. 9, starch is agglutinated without enzyme being added in the starch-dispersing cooker (e.g., cooking vessel 4). After agglutination, enzyme is added in measured quantities to the paste according to the output of the starch cooker and is worked homogeneously using a static mixer. After a variable dwell time, by means of corresponding pipework, the enzyme is deactivated by increasing the temperature. In this case, the advantage is that [0135] a) The starch is agglutinated with almost no molecular weight reduction in the starch-dispersing cooker (e.g., cooking vessel 4), and [0136] b) With the subsequent enzyme treatment, the starch properties, such as viscosity and degree of digestion, can be set individually to customer needs.

[0137] Moreover, subsequent use can also be influenced by the shear energy input in the starch-dispersing cooker (e.g., cooking vessel 4).

[0138] FIG. 9 shows a unit in which the previously-described embodiment of the method according to the invention can be implemented.

[0139] The unit that is shown in FIG. 9 comprises a cooking vessel 4 (“starch-dispersing cooker”), which can be designed like the cooking vessel 4 that is shown in FIG. 8. A line 20, through which enzyme is fed from an enzyme supply container 21 using a pump 22, empties into the cooking vessel 4 (not in accordance with the invention).

[0140] Using a pump 24, starch is conveyed into the cooking vessel 4 via another line 23.

[0141] Steam is introduced into the cooking vessel 4 through a line 25.

[0142] Starch that is digested to form paste is drawn off from the cooking vessel 4 via a line 26. Enzyme is admixed from a supply container 28 (using a pump 29) in front of a static mixer 27.

[0143] Water as sealing water for the sliding-ring seal 43 can be fed into the lower area of the cooking vessel 4 via a line 30 that is supported by a pump 31.

[0144] Below, examples of the method according to the invention are reproduced:

EXAMPLE 1

[0145] Wheat starch (Collamyl 7411) with 13% moisture is mixed with water in order to create a slurry with 30% by weight of content of wheat starch. The slurry thus obtained was agglutinated with a throughput of 750 l/h at a cooking temperature of 115° C. in a device according to FIG. 9. Immediately behind the device according to FIG. 9, the enzyme V Warozym A152 was added in measured quantities in front of a static mixer in a constant amount of 4.28 l/h. The rotor 42 used in the device according to FIG. 9 had a height of 7 mm.

[0146] At a rotor speed of 4,200 rpm with a rotor 42, whose diameter was 130 mm, a paste with a viscosity of 12,500 mPas was created, with the motor driving the rotor 42 having a power consumption of 35 amperes.

EXAMPLE 2

[0147] The procedure was carried out as indicated in Example 1, wherein the rotor speed was increased to 4,400 rpm, and the power consumption of the motor was 41 amperes. A paste with a viscosity of 9,700 mPas was created.

EXAMPLE 3

[0148] The procedure was carried out as in Example 1, wherein the rotor speed was increased to 4,400 rpm, and the enzyme was added in the amount of 2.14 l/h. A paste with a viscosity of 9,500 mPas was created.

EXAMPLE 4

[0149] The procedure was carried out as indicated in Example 3, wherein the amount of enzyme added was increased to 4.28 l/h. A paste with a viscosity of 7,800 mPas was created.

EXAMPLE 5

[0150] The procedure was carried out as indicated in Example 3, wherein the amount of enzyme added was increased to 8.56 l/h. A paste with a viscosity of 7,400 mPas was created.

EXAMPLE 6

[0151] The procedure was carried out as indicated in Example 1, wherein the procedure was carried out at a rotor speed of 4,400 rpm and a rotor 42 with a diameter of 130 mm. The reaction temperature was set at 100° C., with the motor driving the rotor 42 having a power consumption of 38 amperes. The paste that was obtained had a viscosity of 13,950 mPas.

EXAMPLE 7

[0152] The procedure was carried out as indicated in Example 6, wherein a reaction temperature was set at 115° C. The power consumption of the motor was 35 amperes. The paste had a viscosity of 9,700 mPas.

EXAMPLE 8

[0153] The procedure was carried out as indicated in Example 1, wherein the reaction temperature was 115° C., and the rotor 42 operated at a speed of 4,400 rpm. The rotor 42 had a diameter of 130 mm and a height of 5 mm. The power consumption of the motor was 37 amperes. A viscosity of the paste of 10,700 mPas was achieved.

EXAMPLE 9

[0154] The procedure was carried out as indicated in Example 8, wherein a rotor 42 with a height of 7 mm was used, and the power consumption of the motor was 41 amperes. As a result, a paste with a viscosity of 9,700 mPas was created.

EXAMPLE 10

[0155] Potato starch (Collamyl 9100) with 13% moisture was brought into water in order to obtain a slurry with 20% by weight of potato starch. The slurry thus obtained was agglutinated with a throughput of 750 l/h at 115° C. in a device according to FIG. 9. The enzyme from Example 1 was added behind the device according to FIG. 9 but also in front of the static mixer.

[0156] The slurry that exits from the device according to FIG. 9 was routed through a plug flow reactor with a reaction length of 7,500 mm. As a result, a paste with a viscosity of 1,660 mPas was created, and the starch paste created was clear and optimally dissolved.

EXAMPLE 11

[0157] The procedure was carried out as in Example 10, with the proviso that the reaction length of the plug flow reactor was 10,000 mm. The viscosity of the starch paste created was 1,540 mPas. The starch paste was clear, and the starch was optimally dissolved.

EXAMPLE 12

[0158] The procedure was carried out as in Example 10, wherein a slurry of 25% by weight of potato starch was used. The starch paste created was clear, and the starch was optimally dissolved.

EXAMPLE 13

[0159] Wheat starch with a moisture of 13% was mixed with water to form a 30% slurry and cooked at 98° C. in a device according to FIG. 9. The height of the rotor in the device according to FIG. 9 was 7 mm. The enzyme (Warozym A152) was added in measured quantities directly behind the device according to FIG. 9, and after the slurry exited from the device according to FIG. 9, a temperature of 95° C. was maintained. Then, post-dilution was done with 60° C. water and a throughput of 240 l/h. At a constant rotor speed of 4,200 rpm and an addition of enzyme of 1,400 ml/h, a viscosity of the paste of 440 mPas could be achieved.

EXAMPLE 14

[0160] The procedure was carried out as in Example 13, wherein an addition of enzyme was applied in the amount of 1,800 ml/h. The viscosity of the starch paste that was obtained was 240 mPas.

EXAMPLE 15

[0161] The procedure was carried out as in Example 13, wherein the amount of enzyme added was increased to 2,200 ml/h. The viscosity of the starch paste obtained was 140 mPas.

EXAMPLE 16

[0162] The procedure was carried out as in Example 13, wherein a rotor speed of 3,800 rpm and a rotor with a diameter of 130 mm were used. A viscosity of the paste of 580 mPas was achieved.

EXAMPLE 17

[0163] The procedure was carried out as in Example 17, wherein a rotor speed of 4,200 rpm has been applied. A starch paste with a viscosity of 270 mPas was created.

EXAMPLE 18

[0164] The procedure was carried out as in Example 16, wherein the rotor speed was increased to 4,800 rpm. A viscosity of the starch paste of 250 mPas was achieved.

EXAMPLE 19

[0165] The procedure was carried out as in Example 16, wherein a rotor speed of 5,000 rpm has been applied. The starch paste created had a viscosity of 180 mPas.

EXAMPLE 20

[0166] Cationized potato starch (Cationamyl 9853K) was mixed with water to form a slurry with 7.5% potato starch. The slurry thus obtained was cooked at 98° C. with a throughput of 500 l/h in a device according to FIG. 9 and then post-diluted to a 4% content. In this example, better digestion was achieved with higher consistency because of the inner friction. This could be ascertained visually by examination by microscope.

EXAMPLE 21

[0167] A slurry with 15% content of potato starch was processed as in Example 20, wherein it was cooked at 110° C. in the device according to FIG. 9. With higher paper strengths, the starch paste achieved a lower porosity, which was ascertained by means of a lab sheet.

[0168] In summary, an embodiment of the invention can be described as follows:

[0169] With a method for digesting starch (native starch or processed starch, such as cationic starch), an aqueous slurry of the starch is treated with steam in a cooking vessel 4 and in this case exposed to shear forces, wherein the starch-containing slurry is heated to a temperature of between 85° C. and 110° C. in the cooking vessel 4 by introducing steam, and the digestion step is implemented until the desired degree of digestion has been reached.