Abstract:
A method for coating edible particles in a rotary chamber which includes the steps of contacting the particles with a coating solution, then contacting the particles with drying air. The drying air includes at least 3.8 grams of water per kilogram of air.

Description:
TECHNICAL FIELD  
       [0001]     The invention relates to apparatus and methods of coating particles, especially for manufacturing confectionery.  
       BACKGROUND OF THE INVENTION  
       [0002]     Confectionery in the form of granules is known, comprising a center (peanut, chocolate, etc.) and coated with successive hard layers of sugar. These layers are put in place by spraying a sugar syrup onto the centers placed in a rotating chamber. Next, a flow of air inside the chamber makes it possible to dry the sugar layer coating each center. The successive layers are put in place by multiplying the number of spraying drying cycles.  
         [0003]     However, in order to obtain proper drying, the known methods require relatively high product temperatures such that some heat-sensitive centers prove to be awkward to coat properly. So that they have an acceptable appearance at the end of manufacture, especially in terms of color and brightness, the drying cycles must be quite long. For other products which withstand heat better, the flow rate of drying air, at an identical temperature, is too high.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     One aim of the invention is to provide a more efficient coating method.  
         [0005]     For the purpose of achieving this aim, provision is made according to the invention for a method of coating edible particles in which, in a moving chamber: the particles are placed in contact with a coating solution, then, the particles are placed in contact with the drying air, in which the drying air comprises less than 3.8 g of water per kilogram of air.  
         [0006]     Thus, the drying operation is optimized by the use of drier air having, for example, a dew point generally below 0° C.  
         [0007]     The dew point and the blown air temperature condition the temperature in the product bed during drying: the lower this dew point, the lower the temperature in the product bed, which makes it possible to maintain the quality of heat-sensitive products, such as for example chocolate beans. For example, by going from a dew point of +5° C. to a dew point of −15° C., it is possible to lower the temperature of the product bed by about 4° C., which makes it possible to preserve the quality of heat-sensitive products.  
         [0008]     With air having a low dew point, it will also be possible to increase the temperature of the blown air even for a heat-sensitive product and therefore to have more efficient drying, or to keep the same drying efficiency but to decrease the volumes of blown air.  
         [0009]     Reducing the volumes of air required for the process therefore makes it possible to very substantially decrease the size of the air treatment stations, therefore to decrease the investment burden, to simplify the workshops and also to save some energy.  
         [0010]     Thus, by keeping the same blown air temperatures, it was possible to halve the volumes of air required for the drying process. By combining the use of dry air and the increase in the temperature of the blown air, it is possible to reduce the volumes of air required even further.  
         [0011]     Finally, the use of air with a low dew point provides much better drying control, better stability of the process and hence improved and more constant product quality.  
         [0012]     Furthermore, the method according to the invention may have at least one of the following characteristics: 
    the drying air comprises less than 3.5 g of water per kilogram of air;     the drying air comprises less than 2.5 g of water per kilogram of air;     the drying air comprises less than 20 g of water per kilogram of air;     the drying air comprises less than 1 g of water per kilogram of air;     the drying air has a dew point less than −15° C.;     the drying air has a temperature between 15 and 85° C.;     the drying air has a temperature between 20 and 40° C.;     the coating solution comprises at least one sugar;     the coating solution comprises sucrose;     the coating solution comprises a sugar substitute compound;     the coating solution comprises a polyol and/or sugar alcohol compound.    
 
         [0024]     According to the invention, provision is also made for an apparatus for coating edible particles, comprising: 
    a chamber capable of being made to move;     means for bringing a coating solution into contact with the particles contained in the chamber; and     drying means for bringing the drying air into contact with the particles in the chamber,     in which the drying means are capable of bringing the air comprising less than 3.8 g of water per kilogram of air into contact with the particles.    
 
         [0029]     Advantageously the drying means are capable of bringing the air comprising less than 3.5 g of water per kilogram of air into contact with the particles.  
         [0030]     Advantageously the drying means are capable of bringing the air comprising less than 2.5 g of water per kilogram of air into contact with the particles.  
         [0031]     Advantageously the drying means are capable of bringing the air comprising less than 2 g of water per kilogram of air into contact with the particles.  
         [0032]     Advantageously the drying means are capable of bringing the air comprising less than 1 g of water per kilogram of air into contact with the particles.  
         [0033]     Advantageously the chamber is mounted so that it can rotate about an axis, the apparatus comprising an air circulation duct having a body and an end part perforated with orifices capable of extending over the low part of the chamber.  
         [0034]     Coating apparatus comprising a tube with such an end part perforated with orifices are known.  
         [0035]     Furthermore, for the purpose of improving the drying efficiency, provision is made according to a first preferred embodiment of the invention for the end part to be a shoe having, in a plane perpendicular to a direction radial to the axis, a cross section which is greater than the cross section of the body.  
         [0036]     Thus, this end part provides considerable dispersion of the drying air within the particles. Furthermore, during this dispersion, it provides considerable agitation of the particles. By virtue of its large area for exchange with the particles, this end part continuously dries a large number of particles, which improves the uniformity of the drying.  
         [0037]     Furthermore, the apparatus may have at least one of the following characteristics: 
    the shoe has a width parallel to the axis, which is greater than the width of the body;     the shoe has a length in a plane perpendicular to the axis and substantially perpendicular to the radial direction, which is greater than the length of the body;     the body is closer to the rear of the shoe than to the front, with reference to a normal direction of rotation of the chamber;     the shoe has a width, parallel to the axis; narrowing toward the front from the body with reference to a normal direction of rotation of the chamber;     the shoe has a width, parallel to the axis, narrowing in the direction of the body, from a region of greater width;     the shoe has a width, parallel to the axis, narrowing in the direction away from the body, from a region of greater width;     the duct has a front flange lying generally in a radial plane from the shoe to the body;     the shoe has the overall shape of a disk, the plane containing the diameter of which is perpendicular to the axis of the body;     the diameter of the disk is greater than the diameter of the body;     the shoe has the overall shape of a crescent;     the virtual axis connecting the two tips of the crescent extend in parallel with reference to the normal axis of rotation of the chamber and is coincident with a radial plane of the tube;     the tips of the crescent are curved in the direction of the body;     the chamber comprises a peripheral wall, two end walls, and at least one deflector extending from the peripheral wall.    
 
         [0051]     Coating chambers fitted with such a deflector are known. This type of deflector is intended to promote agitation of the particles in order to produce uniform coating and drying thereof. However, the known deflectors, often lying in a plane radial to the axis of rotation of the chamber, are difficult to clean.  
         [0052]     Another aim of the invention is to provide a chamber which is easier to clean.  
         [0053]     For the purpose of achieving this aim, provision is further made for the or each deflector to have a shape perpendicular, at least locally, to a direction radial to the axis.  
         [0054]     Furthermore, the invention may have at least one of the following characteristics: 
    the or each deflector is flat;     the or each deflector is contiguous with only one of the end walls;     the or each deflector extends from a point of the peripheral wall away from one of the end walls, to another point of the other end wall away from the peripheral wall;     the apparatus comprises at least two deflectors;     the two deflectors are flat and parallel;     the peripheral wall is cylindrical;     at least one inner face of the chamber is covered with elastomer;     the particles are food particles;     the particles are items of confectionery.    
 
         [0064]     In this case, the particles in question could be intended to form part of ingestible elements. It could involve food granules for humans or animals. It could especially involve confectionery. The invention is also applicable to coating pharmaceutical compositions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0065]     Still other advantages and characteristics of the invention will become apparent from the following description of a preferred embodiment given by way of nonlimiting example. In the appended drawings:  
         [0066]      FIG. 1  is a view in axial section of a coating apparatus according to the invention;  
         [0067]      FIG. 2  is a left-hand view of the apparatus of  FIG. 1  in cross section;  
         [0068]      FIGS. 3, 4  and  5  are face, left and top views of the shoe of the apparatus of  FIG. 1 ;  
         [0069]      FIG. 6  is a view similar to  FIG. 1  showing the deflectors;  
         [0070]      FIG. 7  is a top view of the apparatus of  FIG. 6 ;  
         [0071]      FIG. 8  is a perspective view of a second embodiment of the shoe for the apparatus;  
         [0072]      FIG. 9  is a perspective view of a third embodiment of the shoe of the apparatus;  
         [0073]      FIG. 10  is a representation in perspective of another exemplary embodiment of the chamber of the apparatus; and  
         [0074]      FIG. 11  is a representation in section and in perspective of the embodiment of  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0075]     In the present example, the method according to the invention is applied to the manufacture of confectionery. It involves granules of the M&amp;M&#39;s® type comprising a center coated with hard layers of sugar syrups. In order to provide this coating, the centers are placed in a rotating chamber, the syrup is sprayed onto the centers, then air is made to flow within the particle bed in order to dry the syrup coating the centers. According to the invention, this air is particularly dry. It has less than 3.8 g of water per kilogram of air. Preferably it has between 0.5 and 1 g of water per kilogram of air, which provides it with a relative humidity of less than 5% at a temperature of 20° C. and a dew point of less than −15° C. With such drying air, the temperature of the particle bed can be lowered, especially if the particles are sensitive to heat.  
         [0076]     The amount of moisture in the drying air will advantageously be less than 2.5 g of water per kilogram of air and preferably less than 1.5 g, or even less than 1 g. The flow of drying air will advantageously be between 1 and 10 m 3 /h per kg of dry product.  
         [0077]     Prior to its introduction into the chamber, the air will undergo a treatment to dry it, preferably by chemical means. This will involve, for example, treatment by bubbling though a lithium-chloride-based liquid phase, as proposed by KATHABAR or else treatment by contact with a silica-gel-based solid phase, as proposed by MUNTERS. Such treatments are known per se and will not be described here.  
         [0078]     An apparatus for implementing the method according to the invention will now be described.  
         [0079]     With reference to  FIGS. 1 and 2 , the apparatus  2  comprises a drum or chamber  4  having a cylindrical peripheral wall  6  with an axis  8  and two, left and right, end walls  10 ,  12  in the overall shape of a flat disk. The chamber is mounted so that it can rotate about its axis  8  and is driven in rotation by suitable motorized means. It comprises a duct for introducing centers to be coated into the chamber and an opening for removing the coated particles, which have not been illustrated.  
         [0080]     With reference to  FIGS. 6 and 7 , the chamber comprises deflectors  14 , in this case there are two of them and they are identical. Each deflector  14  is flat. It is limited on one side by an elliptical arc-shaped edge  16  and on the other by a straight edge  18  perpendicular to the major axis of the ellipse. Each deflector is joined by its straight edge  18  to a respective straight edge of the end walls  10 ,  12 . The straight edge is at some distance from the cylindrical wall  6 , except at its two ends, which are located at the junction of the cylindrical wall  6  and the end wall. The elliptical arc-shaped edge is joined to the cylindrical wall  6  and at some distance from the other end wall.  
         [0081]     In profile, as in  FIG. 6 , each deflector  14  is inclined with respect to the axis  8  and to the generatrix of the cylinder. It is inclined in the direction of the end wall to which it is not joined. The two deflectors are parallel to each other. Each deflector isolates and closes off a region  20  of the chamber from the rest of the chamber. The particles cannot access these two regions. The two deflectors  14  provide considerable agitation of the particles from left to right and from right to left during the coating and drying when the chamber is rotating.  
         [0082]     In this case, the chamber will be free of orifices or perforations on the cylindrical wall, the end walls and the deflectors being intended to allow liquids and gases through while retaining the particles. However, the chamber could alternatively comprise such perforations.  
         [0083]     With reference to  FIGS. 1 and 3 , the apparatus comprises an air inlet duct  22  and an air outlet, for example in the form of a grille or a duct  24 . The chamber is constructed with connection means capable of turning while these ducts remain fixed. The duct  22  comprises an inner tube bent at the body  26  having an end part or shoe  28  capable of lying in the lower half of the chamber, within the particle bed  30 . The bent inner duct  26  is able to rotate about an axis  11  parallel to the axis  8  so that it can be raised into the upper part of the chamber by rotating the shoe. Above the shoe, the tube  26  has a cylindrical shape.  
         [0084]     A preferred shape of the shoe  28  will now be described. With reference to  FIGS. 3, 4  and  5 , the shoe has a central region  32  with vertical faces. This central region  32  is the largest cross section of the shoe in a plane perpendicular to a direction substantially radial to the axis and this cross section is greater than the corresponding cross section on the tube  26 . Thus, the length L of the central region  32 , in a plane perpendicular to the axis  8  and substantially perpendicular to the radial direction, is greater than the diameter d of the tube  26 . Similarly, the width l of the central region  32 , parallel to the axis  8  is greater than the diameter d. Furthermore, the length L is in this case equal to about twice the width l. The shoe  28  has an upper region  34  forming the junction between the central region  32  and the tube  26 . This region  34  flares from the tube to the central region. Similarly, it has a lower region  36  which shrinks toward the bottom and forms a ridge  37  parallel to the length L. Furthermore, the tube comprises a front flange  40  extending from the upper region  34  to the tube  26 . This flange lies in an essentially radial plane and has a triangular shape. A rear vertical edge of the flange runs alongside the tube  26 , another lower edge runs alongside the upper region  34 . The shoe has an overall shape which is flattened in the radial direction, that is to say widened perpendicular to this direction.  
         [0085]     Other shapes of shoes  28  can be envisioned.  
         [0086]     In a second embodiment, the shoe  28  will have an overall disk shape. With reference to  FIG. 8 , the shoe has a central region  32 , with the largest cross section of the shoe, in a plane perpendicular to a direction which is substantially radial to the axis  8 . This cross section is greater than the cross section of the tube  26 . Thus, the length L of the central region  32 , in a plane parallel to the axis  8 , is greater than the diameter d of the tube  26 . Furthermore, the length L is in this case equal to about four times the width d. The shoe  28  has an upper region  34  forming the junction between the central region  32  and the tube  26 . This region  34  flares, with for example an ovoid curvature, from the tube to the central region. Similarly, it has a lower region  36 , narrowing down from the region  32  to the lower end of shoe with, for example, the same ovoid curvature. The shoe has an overall shape which is flattened in a direction perpendicular to the radial direction, that is to say, widened parallel to the axis  8 .  
         [0087]     In a third embodiment, the shoe  28  will have the overall shape of a crescent. With reference to  FIG. 9 , the shoe has a central region  32 . The general profile of the region  32  in a radial direction is in the shape of a parabola turned toward the tube  26 . The plane containing the profile of the parabola contains the axis of the tube  26 . The length L of the central region  32 , in a plane perpendicular to the axis  8  and substantially located at right angles to the junction (tube  26 -shoe  28 ), is greater than the diameter d of the tube  26 . Similarly, the width D of the central region  32  at right angles to the tips of the crescent, parallel to the axis  8 , is greater than the diameter d. Furthermore, the length D is in this case equal to about three times the width L.  
         [0088]     The shoe  28  has an upper region  34  forming the junction between the central region  32  and the tube  26 . This region  34  flares and curves back from the tube up to the central region. Similarly, the length of the region  34  in a series of planes perpendicular to the axis  8  shrinks from the junction region (shoe  28 -body  26 ) to the tips of the crescent turned toward the tube  26 . Furthermore, the tube  28  has a lower region  36  narrowing down from the region  32  to the lower end of the shoe. The virtual axis  37  connecting the two tips of the crescent preferably lies parallel to the normal axis of rotation of the chamber and falls within a radial plane of the tube  26 .  
         [0089]     The operation of the three embodiments of the shoe is similar.  
         [0090]     The inside of the shoe  28  communicates with the tube  26 . The shoe is perforated with orifices  39  on its central  32 , upper  34  and lower  36  regions, except at the front parts of these three regions and except at the rear parts of the upper and central regions. The shoe thus forms a large area for exchange with the particle bed  30  in which it is submerged. The shoe is placed such that it lies always at some distance from the deflectors  14  and midway between the end walls  10 ,  12 .  
         [0091]     In this instance, the orifices have a diameter of 7 mm and a difference between axes of 8.5 mm. The exchange surface area of the shoe extends over 0.2357 m 2  with 45% void. The speed of the air through the orifices is 11 m/s.  
         [0092]     The apparatus comprises known means  42 , especially a nozzle means, for introducing a coating syrup, in this case based on sugar, into the chamber and spraying it.  
         [0093]     When the method is implemented, the centers  30  to be coated are introduced into the rotating chamber  4 , then the coating syrup is sprayed onto the moving centers. Next, the spraying is interrupted and dry air is injected into the bed of coated centers by means of the shoe  28 . The moisture-laden air is removed via the duct  24 . During rotation, the two deflectors  14  agitate the particles from left to right and from right to left. The shoe  28  injects drying air into the particle bed. This air passes through the bed to be removed via the duct  24 . When drying is complete a new coating cycle is started and so on until a hard layer of the desired thickness is obtained.  
         [0094]     Advantageously, the external faces of the shoe  28  and of the deflectors  14  and the internal faces of the chamber  4 , that is to say all the faces intended to be in contact with the particles, can be coated with food-grade rubber so as to limit the risk of damage to these faces during coating, by knocks and impacts, to a minimum.  
         [0095]     The invention could be implemented, for example, as follows.  
         [0096]     The centers are peanuts coated with chocolate and sugar. Furthermore, the coating makes it possible to produce a crisp, colored and bright sugar shell. In the finished product, the percentages by mass are:  
                                                       peanut:   24%           chocolate:   48%           sugar coating:   28%                      
 
         [0097]     The syrup has the following compositions by mass:  
                                                       sugar solution (74% sugar, 26% water):   91.5%           water:    1.4%                      
 
         [0098]     To treat 1048 kg of centers, thirty syrup applications, each of 7.2 liters, are performed, with drying lasting from 6 to 15 minutes each time, depending on the appearance that the granules are to be given.  
         [0099]     The drying air is blown at a temperature of 23.5° C. It contains 1 g of water/kg of air and has a dew point of −15° C.  
         [0100]     The flow rate is 3400 m 3 /h for the twelve applications. This flow rate corresponds to a quantity of air of 9.4 m 3 /h/m 2  of surface area of the centers to be coated. In general, provision can be made for the flow rate to be between 1 and 24 m 3 /h/m 2  of surface area of the centers to be coated, advantageously between 4 and 15 m 3 /h/m 2  and preferably between 7 and 12 m 3 /h/m 2  of surface area of the centers to be coated.  
         [0101]     Of course, numerous modifications may be made to the invention without departing from the scope thereof.  
         [0102]     The shoe  28  can be implemented independently of the use of particularly dry drying air or of the deflectors  14  described above.  
         [0103]     Thus, it is possible to envision a particle-coating apparatus  2  comprising a chamber  4  mounted so as to rotate about an axis  8  and an air circulation tube  22  having a body  26  and an end part  28  perforated with orifices  39  capable of extending into the lower part of the chamber, in which, in a plane essentially perpendicular to a direction radial to the axis, the end part has a larger cross section than the cross section of the body.  
         [0104]     Likewise, the deflectors  14  can be implemented independently of the shoe  28  and of the dry air.  
         [0105]     Thus, it is possible to envision a particle-coating chamber  2  mounted so as to rotate about an axis  8 , and comprising: 
    a peripheral wall  6 ;     two end walls  10 ,  12 ; and     at least one deflector  14  extending from the peripheral wall, in which the or each deflector has a shape locally perpendicular to a plane radial to the axis.    
 
         [0109]     Another exemplary embodiment of a coating chamber is shown in  FIGS. 10 and 11 .  
         [0110]      FIG. 10  shows the outside of the chamber  4 . The chamber  4  comprises a substantially cylindrical peripheral wall  6  bent on one side of the wall  6  at the end wall  10 , for example, and bent on another side of the wall  6  at the end wall  12 . Two openings are made in the walls  10  and  12  to allow the passage of the drying means and of the means for bringing a coating solution into contact (means not shown in  FIGS. 10 and 11 ) embodying an axis  8 .  
         [0111]      FIG. 11  shows the chamber  4  in section. In this figure the tube  26  and a shoe  28 , the shape of which is a disk, are shown. However, any shape of shoe  28 , such as one of those described in the previous developments, for example, could be adapted to the chamber  4  shown in  FIGS. 10 and 11 .  
         [0112]     However, the invention could be implemented by means of a container other than a drum. It could, for example, be a fluidized bed apparatus, a Wurster tube apparatus or a vibrating fluidized bed.  
         [0113]     The invention could be implemented by means of sugars such as sucrose, dextrose, fructose, maltose and glucose. It could be implemented by means of low-calorie sugar substitutes (sweeteners). It could be implemented by means of sugar alcohol and/or polyol compounds, such as for example maltitol or sorbitol. It could also be implemented by means of cellulose compounds.