Abstract:
The apparatus comprises a kneading channel slanting downwards from an upstream inlet end, which is open to receive curd to be kneaded, to a downstream outlet end, which is open to unload the curd. A pair of opposed augers are pivotally supported side-by-side in the kneading channel and are operatively connected to motor elements for rotating in opposite directions and moving the curd to the downstream end. First stem blowing elements are open to the kneading channel. A kneading chamber with plunger arms is arranged at the outlet end of the kneading channel for receiving the curd unloaded from the channel.

Description:
[0001]    The present invention relates to a curd kneading apparatus for production of pasta-filata cheese. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the production of pasta-filata cheese, the curd is made plastic or “stringy” by heating it up to a temperature of at least 60° C., typically by mixing the curd with hot water. Thereafter, the stringy curd is kneaded in order to obtain a fibrous paste, which is then broken into globes or cylinders which are successively hardened by cooling. 
         [0003]    The kneading process is generally carried out by a machine in which the curd, after being minced, is loaded into a kneading chamber into which hot water is also fed. Plunging arms operating in the kneading chamber mix and stretch the paste growing up by the mix of curd and hot water. The paste produced in the kneading chamber is progressively fed to subsequent molding operations, while the water in excess is drained from the kneading chamber through a draining hole. 
         [0004]    However, with the above process, the water-soluble nutritive substances, such as fat, albumine or glucose, which are generally contained in small percentages in the curd to be kneaded, inevitably dissolve in the hot water used during the kneading process. Therefore, the water drained from the kneading chamber through the draining hole contains these substances, which are consequently lost, thereby resulting in a reduction of the production yield. Moreover, the water to be disposed must be firstly skimmed, in order to recover the above substances, and then purified so that it can be discharged without incurring environmental pollution problems, which operations introduce considerable complications in the process. 
         [0005]    Another drawback of the above machine provided with plunging arms is that a considerable power is required to heat the water, which water is used in high percentages (two parts of water per each part of paste), with consequent rise in the production costs. 
         [0006]    With other types of known machines, attempts have been made to knead the curd by augers. However, such known machines had a discountinous operation and, consequently, a low production yield. 
       SUMMARY OF THE INVENTION 
       [0007]    Therefore, it is a main object of the invention to provide a curd kneading apparatus which is capable of producing all types of pasta-filata cheese with a desired moisture degree, generally in the range 45% to 65%, without losing the water used in the kneading process, so that all the nutritive substances are retained in the paste and, at the same time, potentially polluting process wastes are eliminated. 
         [0008]    It is another object of the invention to provide a kneading apparatus which is capable of operating continuosly in such a way as to increase the productivity and the production yield. 
         [0009]    The above objects and other aims and advantages, which will better appear from the following description, are achieved by a curd-kneading apparatus for production of pasta-filata cheese having the features recited in claim  1 , while the dependent claims state other advantageous, though secondary, features of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention will be now described in more detail with reference to a preferred, non-exclusive embodiment shown by way of non-limiting example in the attached drawings, wherein: 
           [0011]      FIG. 1  is a broken-away view in side elevation of the kneading apparatus according to the invention; 
           [0012]      FIG. 2  is a view in cross-section of the apparatus of  FIG. 1  along line II-II, shown in a greatly enlarged scale; 
           [0013]      FIG. 3  is a view in cross-section of the apparatus of  FIG. 1  along line III-III, shown in a greatly enlarged scale. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    With reference to  FIGS. 1 to 3 , the kneading apparatus according to the invention comprises a frame provided with columns such as  10  which support a kneading channel  12  closed by a removable cover  13 . A pair of parallel augers  14 ,  16  are arranged side-by-side in the channel and have their screw profiles wound in opposite directions and partially inserted into each other ( FIGS. 2 ,  3 ). As shown in detail in  FIG. 2 , the inner wall  12   a  of channel  12  is shaped such that it surrounds the external profile of augers  14 ,  16 . Augers  14 ,  16  are driven to rotate in opposite directions by a motor  18  provided with a reduction unit  19 , both of which are covered by a carter  20 , via a mechanical transmission  21  provided with conventional sealing means  22 . 
         [0015]    As shown in  FIG. 1 , channel  12  with augers  14 ,  16  housed therein are sligthly slanting downwards from an upstream inlet end  23  of channel  12  to a downstream outlet end  24  thereof, at an angle which is advantageously in the range 2° to 10°, preferably 4°. Each of the opposite side walls of channel  12  has an array of stem injectors  25  ( FIG. 2 ) connectable to a stem source (not shown). Preferably, each array comprises six injectors  25  which are equally spaced along the respective wall of channel  12 . The injectors are connected to a pneumatic needle valve (not shown) which is operable to enable/disable the feeding of stem into the channel. A temperature sensor  26  is also installed in channel  12  ( FIG. 2 ) for measuring the temperature therein. 
         [0016]    The downstream end  24  of channel  12  leads to a kneading chamber  27  having two side walls  28   a,    28   b,  one of which,  28   a,  is provided with an openable inspection window  29 , an U-shaped bottom wall  30 , an upper wall  32 , a rear wall  34  and a front wall  36  having an outlet mouth  38 . 
         [0017]    Two horizontal, parallel spindles  44 ,  46  are housed in the kneading chamber and are driven by a reduction gear  40 , which is anchored to rear wall  34  and is driven a motor  42 , to rotate in opposite directions at a predetermined speed. Two short cranks  48 ,  50  projecting from spindles  44 ,  46  are hinged to respective bent arms  52 ,  54  at intermediate positions thereof. The arms are longitudinally offset from each other, and are hinged to each other at their upper ends in  56 . Accordingly, arms  52 ,  54  cooperate with cranks  48 ,  50  to form a linkage which drives the lower ends of the arms along specular orbital paths. Parallel shoves  58 ,  60  project at rigth angles from the lower ends of the two arms  52 ,  54  into the kneading chamber  26  in the direction facing away from channel  12 , and substantially engage the whole length of chamber  27 . Arms  52 ,  54  differ from each other in their vertical size to prevent shoves  58 ,  60  from interfering with each other during their orbital movement. Shove  60  preferably has a few transversal comb-like tines  62  ( FIG. 2 ). 
         [0018]    Two steam injectors  63   a,    63   b  ( FIGS. 1 ,  3 ), which are identical to injectors  25  in channel  12 , are respectively mounted on rear wall  34  and front wall  36  of chamber  27 . Steam injectors  63   a,    63   b  are connectable to the above-cited steam source and are controlled by a central unit CU on the basis of a second temperature sensor  65 . A hot water feeding duct  67  leading to chamber  27  is connectable to a hot water source (not shown) which, if required, may be occasionally enabled to feed small amounts of hot water into the chamber, depending on the circumstances. 
         [0019]    Channel  12  is loaded with curd (which has been previously minced, e.g., by a conventional blade mincer, not shown), at its upstream end  22  via a substantially vertical loading duct  64 . 
         [0020]    The operation of the augers and of the steam injectors is preferably controlled by control unit CU on the basis of the information received from the temperature sensors (which is only diagrammatically shown in  FIGS. 2 ,  3 ) in a way known to a person skilled in the art. 
         [0021]    The above-described apparatus operates as follows. Minced curd is loaded into channel  12  via duct  64 . Augers  14 ,  16 , by rotating in opposite directions, progressively convey the curd towards outlet end  24  of the channel and, at the same time, apply a preliminary kneading action upon the curd, mainly by compression. At this stage, injectors  25  feed steam into channel  12 , thereby causing the curd to progressively heat and become stringy, i.e., plastic. Since the steam is absorbed more easily by the paste then the water, this steam-based heating system considerably reduces the amount of water released by the paste in the channel, with consequent increase in the production yield. Moreover, due to the inclination of channel  12 , any released water flows downstream by gravity rather than stagnating in the first portion of channel  12  (with consequent accumulation to be drained). This circumstance favours the uniform absorption of water by the paste under processing in channel  12 . Preferably, the injection of steam is automatically controlled by control unit CU on the basis of the signal received by temperature sensor  26 , in a way that will be obvious to the person skilled in the art. 
         [0022]    Any fraction of water which is not absorbed by the paste in channel  12  flows into kneading chamber  27 , wherein the paste, after the partial kneading action received by the augers, is subjected to a further kneading action. Plunging arms  52 ,  54 , unlike the augers which mainly act by compression, lift and stretch the paste while further steam is fed by injectors  63   a,    63   b,  always on the basis of the signal received by temperature sensor  65 . If required, the degree of humidity of the paste can be further increased by supplying small amounts of hot water via duct  67 . 
         [0023]    By adjusting the amount of steam and water (from duct  67 ) supplied during the kneading process, a pasta-filata with a desired degree of humidity, substantially in the range 45% to 65%, can be obtained. In the practice, it has been found that the pasta-filata produced with the apparatus of the invention retains all the kneading water, so that no drainage is required. Moreover, the apparatus of the invention is also advantageous from the point of view of the power consumption because the steam-based heating system does not required to heat great amounts of water, which water, in the known machines, was largely lost. 
         [0024]    It is evident from the description that the apparatus of the invention achieves the declared scope of producing a soft, moist paste-filata without drainage of water, with consequent increase in the production yield and in the quality of the product. Furthermore, the above-described apparatus is capable of operating continuosly becase the paste fed to chamber  27  has been already kneaded by the augers and, therefore, just a finishing kneading is required which can be carried out without interrupting the feeding of paste. 
         [0025]    Of course, the above-described preferred embodiment of a kneading apparatus according to the invention can be largely changed. For instance, the number and the arrangement of plunging arms and steam injectors in channel  12  and in chamber  27  can be varied. Moreover, the steam injectors can have any known structure suited to perform the required function. Furthermore, a plurality of kneading chambers with plunging arms can be arranged in series downstream of the channel.