Patent Abstract:
A baker&#39;s oven  10  and a method of operating the baking oven  10 . The baking oven  10  including heating means  50  arranged to underlie baking trays  31  to provide a substantial proportion of the heat to the baking trays  31  than to other portions of the oven, a temperature sensor  62  for providing a signal indicative of oven temperature. An interface  60  is adapted to receive information from a baker indicative of a bake program and information corresponding to products being loaded into the oven. The control means  61  is operatively connected to the heating means  50 , the temperature sensor  62  and the interface  60  to receive signals corresponding to oven variables comprising the oven temperature and a fixed baking time indicative of the product. The control means  61  is adapted to deactivate the heating means  50  after a first predetermined portion of the fixed baking time has elapsed in response to the oven temperature reaching a trip temperature.

Full Description:
FIELD OF THE INVENTION 
     The invention relates to a baker&#39;s oven and in particular to the operation of the oven. 
     BACKGROUND OF THE INVENTION 
     A conventional baker&#39;s oven comprises a number of stacked oven compartments with individual oven doors at the front. Each level of the oven includes two side by side compartments, which each have a fixed shelf onto which baking trays or bread pans or a like can be loaded. 
     The oven compartments are heated by electric heating elements mounted bottom and top of each compartment. The heating elements are formed as single heating units comprising a number of parallel arms connected in series by U-shaped elements. The parallel arms extend from the oven door to the rear of the compartment and are spaced across the width of the oven. 
     The top and bottom heating elements can be separately controlled to vary the heat distribution within the oven. For certain types of baked goods, it is advantageous to supply the heat predominantly from the bottom of the oven. The bottom heating elements of conventional baker&#39;s ovens are usually more or less uniformly distributed over the floor of the oven to provide a uniform distribution of heat within the oven. According to conventional baking practice, it is important that a constant temperature is maintained throughout the baking cycle, thus preheating the oven, or allowing the oven to cool prior to loading with product is important. Typically the oven temperature must be kept within 10° C. of an ideal temperature. 
     It is known to use a timer to activate the oven prior to the arrival of the baker at the start of the day, so that the oven is preheated when the baker arrives. While the use of a timer effectively presents an oven at a predetermined temperature at a time set many hours earlier, there are risks (e.g., of fire) associated with activating unattended ovens. Commercially available Multi-deck, Setter ovens, and other such ovens with multiple baking chambers within one chassis, may be capable of baking many different products at the same time. However, it is commercially accepted that these ovens need to be pre-heated to, or above, recipe temperature before loading each product. As there is no fan assistance in most conventional ovens, the heat is typically difficult to control, and the baker must often be familiar with each oven&#39;s characteristics to achieve acceptable results. 
     Different bakery products require different baking temperatures. Therefore the baker&#39;s production schedule is complicated, and the oven utilization is reduced by having to pre-heat/pre-cool an oven prior to baking. The production schedule must be changed so that the oven temperature closely matches the requirements of the next product to be loaded. In busy bakeries, there is often the need to break the usual production cycle (due to rejected product, unexpected orders etc.) and there is also the issue of inexperienced staff needing to run ovens at short notice. Even for the most experienced operator, the issues involved in obtaining the most efficient production schedule are often at odds with what the store&#39;s customer&#39;s demand for fresh full variety of product. 
     A particular problem with controlling oven temperature is “heat over-run”. Heat over-run stems from the thermal inertia of the heating system. Typically the heating elements are much hotter than the air in the oven. Heat is thereby transferred from the elements to the air and is in turn transferred to the bakery product in the oven. Heat over-run occurs after the oven is unloaded and the bakery product is removed. After the bakery products are removed, even if the heating elements are deactivated, heat stored within the elements is transferred to the air within the empty oven. This results in a very hot oven. This heat is not only wasted but results in considerable inefficiency in that the oven may well be too hot for the next batch of products to be loaded, meaning that the oven must then be precooled for the next batch. One approach to the issue is to gradually reduce the power to the heating elements as the oven air temperature approaches a required baking temperature. This means that the elements are not as hot as they might be when the oven is unloaded. 
     Objects of the present invention include to reduce oven preheating/precooling requirements or at least provide alternatives to existing arrangements in the marketplace. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided a baker&#39;s oven including:
         supporting means for supporting one or more baking trays;   heating means arranged to underlie the baking trays to provide a substantial proportion of the heat to the baking trays than to other portions of the oven;   a temperature sensor for providing a signal indicative of oven temperature;   an interface adapted to receive information from a baker indicative of a bake program and information indicative of products being loaded into the oven;   control means operatively connected to the heating means, the temperature sensor and the interface; and   the control means being adapted to deactivate the heating means after a first predetermined portion of a fixed baking time in response to the oven temperature reaching a trip temperature.       

     “Baking time” as used herein refers to the baking time experienced by the product. Typically the baking time commences with product being loaded into the oven and finishes with the issuance of a signal from an indicator means indicative of the end of the cycle (in response to which a baker should remove the product from the oven). The product could be retarded or proofed in a cold oven for a period of time (e.g., overnight). The baking time would then commence with the activation of the heating means. 
     The information indicative of a bake program might simply be the required baking time and a desired temperature (e.g., the trip temperature). Alternatively, the information might simply be an indicator of product type, the control means being configured to calculate the trip temperature and baking time based on the product type. 
     The control means may be adapted to deactivate the heating means after a second predetermined portion of the baking time independently of the oven temperature. 
     Preferably the control means is configured to thermostatically control the heating means. For example, the heating means may be thermostatically controlled to maintain the trip point temperature. 
     The first predetermined portion is preferably between 80% and 90%, and most preferably about 85%, of the baking time. The second predetermined portion is preferably about 95% of the baking time. 
     The trip temperature may be preselected to be about 10 degrees below a high set temperature, the high set temperature being the highest maximum temperature the oven should reach at any time. This temperature is determined by trial and error with the highset temperature being the highest baking temperature of the oven to yield acceptable product. 
     According to another aspect of the invention there is provided a method of operating the baking oven including a heating means arranged to underlie baking trays whereby a substantial proportion of the heat is provided to the baking trays, the method including the steps of heating the heating means according to a bake program indicative of products loaded into the oven, and deactivating the heating means after a first predetermined portion of a fixed baking time in response to the oven reaching a trip temperature. 
     The heating means and the supporting means are preferably relatively moveable to reduce the incidence of localized burning of product on the baking trays proximal the heating means. 
     The supporting means may include a carousel rotatable about a vertical axis. The interior of the oven is preferably substantially free of high thermal inertia objects, such as bulk ceramic material and plate metal fittings, to minimize thermal inertia of the oven interior and thereby improve baking conditions. This ensures that a large proportion and preferably substantially all of the heat supplied by the heating elements arranged according to the invention is supplied directly to productively produce product rather than heating objects, which store and radiate heat. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional side view of a five level rotary baker&#39;s oven in accordance with an embodiment of the present invention; 
         FIG. 2  is a sectional plan view showing one level of a previously disclosed oven; and 
         FIG. 3  is a sectional plan view of one side of one of the levels of the oven of  FIG. 1  showing the heating elements and the baking trays. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It has been discovered that by concentrating the active portions of the heating elements more directly under the baking trays the quality of baked goods and the operation of the baking oven can be improved. This has been found to be associated with supplying the heat more directly to the product. 
     According to an aspect of the invention not expressly claimed herein, there is provided a baking oven having heating elements arranged to underlie baking trays to provide a substantial proportion and preferably substantially all of the heat to an active region under the baking trays than to an inactive region positioned outwardly of the active region. 
     The oven chamber preferably includes heating elements extending from a wall of the oven into the active region, each element having an inactive portion and an active portion, the inactive portion extending from the wall to the active portion, which extends within the active region for more directly heating the underside of the baking trays. 
     In an advantageous arrangement, the oven includes a rotatable turntable for supporting the baking trays. In this instance the active region may be defined by an outer most periphery of the baking tray as it is rotated on the turntable. Alternatively, the active portions of the elements may lie within a region defined by an inner most portion of the outer periphery of the baking trays as they are rotated on the turntable. Preferably the baking trays define a rectangle centered on an axis of rotation of the carousel and the active region boundary is defined as being located between, and most preferably half way between, a circle defined by rotation of an outer most corner of the rectangle and a circle defined by rotation of the nearest approach of an edge of the rectangle about the axis. 
     Preferably the heating elements are arranged to provide more than 2 times, preferably 2.5 to 3.5, and most preferably 2.9 to 3.1, times greater power density to the active region than to the inactive region. 
     Preferably the heating elements are relatively narrow thereby allowing the heating elements to be more densely concentrated within the active region. Each heating element may include two elongate heating element portions, a steam generation chamber positioned intermediate and operably connected to the elongate heating element portions and having at least one steam outlet. 
     Referring to  FIGS. 1 and 2 , the baker&#39;s oven is a rotary oven  10  similar to the type sold under the registered trade mark “ROTEL”. In the embodiment illustrated, the oven has five levels with two oven compartments  11  on each level. A drive motor  12  (not shown) is operably connected to a pair of vertical shafts  13  on which are mounted turntables  14 , which may incorporate optional ceramic “tiles”  15  on which the baking trays (not shown) are cooked. Each oven compartment  11  has an oven door  16  operably openable and closable by a handle  17 . 
     Each oven compartment  11  has top heating elements  18  mounted to the underside of the top wall  19  of the oven compartment  11 . As shown in more detail in  FIG. 3 , each oven compartment  11  has a pair of substantially U-shaped inner heating elements  20  mounted on the bottom wall  19   a . The operation of the heating elements  20  is controlled by a computerized control system (not shown). 
     By selectively energizing the upper heating element  18  and the lower heating element  20  it is possible to control: 
     1. The air temperature within the oven chamber, 
     2. The heat rising directly from the lower heating element  20  to the bottom of the turntable  14  and thus the baking trays  30 , and 
     3. The heat radiating from the upper heating elements  18 . 
     For example by supplying more electrical power to the lower element  20 , it is possible to supply more heat to the bottom of the turntable  14  and thus baking trays  30 . This could be used to produce, for example, a bread having more bottom crust and a darker baked color on top. 
     It has been found that the position of the heating elements has a large bearing on the quality of the baked product. This is thought to be related to the control over the application of heat to the lower surfaces of turntable  14  and baking trays  30 . By concentrating the heating elements under the baking trays, it is possible to provide a more concentrated heat to the underside of the turntable  14  and baking trays  30  and thereby have greater control over the above listed variables. The result is a baking oven, which can be used to produce an improved baked product. 
       FIG. 3  shows a cross sectional plan view of one side of the oven of  FIG. 1 . It shows a potential layout of the heating elements  20  and the relative positioning of the baking trays  30  when in use. The turntable  14  is omitted from this view for clarity. As illustrated the heating elements  20  are relatively narrow elongate members. This allows the heating elements  20  to be more closely spaced and positioned under the baking trays  30 . Only three elements  20  are illustrated here for clarity although of course it is possible to use more. This concentration of heating elements differs from conventional thinking, which would have a number of widely spaced heating element portions evenly distributed across the oven floor to produce a more even distribution of heat throughout the baking chambers. 
     As illustrated in  FIG. 2 , previously disclosed ovens have widely spaced heating elements evenly spread across the baking chamber  11  including providing heating element portions  23  close to peripheral wall  25 . 
     To give an idea of scale, each baking tray  30  is about 18 inches (460 mm) by about 30 inches (720 mm) and the trays are spaced by the shaft  30 , which is about 1 inch (25 mm) thick. Thus the two trays being spaced by the shaft  13  define a rectangle of about 37 inches (940 mm) by about 30 inches (720 mm). This tray size is commonly used in Victoria (a region of Australia). Elsewhere in Australia 405 mm×737 mm is a common tray size. Trays as large as 460 mm×762 mm are sometimes used. 
     Each heating element  20  is provided with an inactive portion  21  and an active portion  22 . The inactive portion  21  does not produce heat. The active portion  22  produces heat. The heating element extends from a wall  120  of the oven with the inactive portion  21  of the heating element providing an inactive region of the oven. The active portion  22  of the heating element extends from the inactive portion  21  into the active region of the oven beneath the baking trays  30 . The active portions have a more or less homogenous construction, but have been found to produce little or no heat along a length of 25 mm or so adjacent the inactive portions  21 . 
     It has been found that an improved distribution of heat within the baking chamber can be achieved by positioning the active portions  22  within the region  40  described by the outer most corner  31  of the baking trays as it is rotated about the shaft  13 . This region is herein referred to as the active region. The shorter heating element  20  is arranged so that the active portion  22  lies predominantly within a smaller active region  41 . The smaller active region  41  is defined by the nearest approach of the farther surfaces  31  of tray  30  to the shaft  13  as it is pivoted about shaft  13 . Innermost active region  42  is defined by the innermost approach of edge  32  of trays  30  as it rotates around shaft  13 . The positioning of the active portions  22  within this innermost active region  42  means that the active regions are always directly underneath the baking tray as it is rotated about shaft  13 . 
     The ideal location of the boundary  140  between the active region and the inactive region is calculated with respect to the nearest and furthest approaches (relative to the central axis  13 ) of the edge  31 , which correspond to the circles  40 ,  41 , such that boundary  140  is halfway between circles  40 ,  41 . Power densities of 0.133 W/cm 2  and 0.4 W/cm 2  in the inactive and active regions respectively have been found to be ideal. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Scenario 1 
                 Scenario 2 
               
               
                   
                 High oven air 
                 Low oven air 
               
               
                 Process 
                 temp bake 
                 temp bake 
               
               
                   
               
             
             
               
                 Oven temp before load (0 min) 
                 230 
                 200 
               
               
                 Oven temp after load (0 min) 
                 210 
                 170 
               
               
                 Oven temp after (10 min) 
                 220 
                 190 
               
               
                   
                 (at trip point) 
               
               
                 Oven temp after (20 min) 
                 220 
                 205 
               
               
                   
                 (at trip point) 
               
               
                 Oven temp at 85% of bake time 
                 220 
                 210 
               
               
                 (25.5 min) 
                 (all heating off) 
               
               
                 Oven temp at 90% of bake time 
                 218 
                 212 
               
               
                 (27 min) 
               
               
                 Oven temp at 95% of bake time 
                 216 
                 216 
               
               
                 (28.5 min) 
                   
                 (all heating off) 
               
               
                 Oven temp at unload (30 min) 
                 214 
                 214 
               
               
                 Oven temp after unloading (30 min) 
                 228 
                 228 
               
               
                   
               
             
          
         
       
     
     Table 1 illustrates the operation of the oven according to a preferred form of the invention. In this example the bakery product is sandwich bread for which a baking time of 30 min and high set temp of 230° C. have been determined through trial and error on this type of oven to be sufficient to produce acceptable product. Two possible scenarios are shown. In scenario 1 the oven is initially relatively hot. Scenario 2 shows an initially cooler oven. 
     In both scenarios a trip point temperature of 220° C., i.e., 10° C. less than the high set temp, is determined. About 30° C. of heat is lost from the oven upon loading. The oven is then thermostatically controlled to maintain, or at least attempt to maintain the trip point temperature. 
     In scenario 1, starting out with a relatively hot oven, the oven cools and reaches trip point temperature 220° C. after 10 min. Thereafter the heating elements are thermostatically controlled to cycle on and off to maintain this temperature. Having reached trip point temperature, the elements are deactivated at 85% of the baking time, i.e., 25.5 minutes. Having cycled on and off between 10 and 25.5 minutes, the heating elements in this scenario are active for a total 23 minutes out of the 30 minute baking time. 
     In scenario 2, starting with a cooler oven, the heating elements operate continuously but the oven does not reach trip point temperature. The heating elements are deactivated at 95% of the baking time, i.e., 28.5 minutes. 
     In both scenarios the bread continues to bake after deactivation of the elements. Residual heat within the oven, including heat stored in the elements is thus absorbed. As a result, upon unloading, the elements are much cooler than they might otherwise be, and heat over-run is substantially reduced. In both scenarios, the heat over-run is only 14° C. (i.e., 214° C. to 228° C.) so that a like batch of bread can be immediately loaded. 
     Both scenarios produce satisfactory bread, indeed the product is essentially indistinguishable. 
     The method of operating and controlling the heating elements is preferably implemented using electronics and software incorporated into the oven. 
     The preferred operation of the oven is as follows: 
     The baker selects the product to be baked, from a menu that is presented as a product name, product category, or as a simple product code or number. These can be presented on the control panel screen as pictures, drawings, or just descriptive names or numbers. In response to the product selection, the controller  61  determines the trip temperature and baking time. 
     Once selected, program lock-outs that will stop the program operating are “MINIMUM LOAD TEMPERATURE” and “MAXIMUM LOAD TEMPERATURE” that may be specific to each product, or sometimes product type. A thermocouple  62  inside the oven chamber is read at regular intervals by the software, and so, for example, an oven chamber that is read as at 120 degrees C. will reject any program for products with a “MINIMUM LOAD TEMPERATURE” above 120 degrees. There may be many products that can bake and produce acceptable product from as low as 20 degrees C., ranging up to 119 degrees C., and any of these can be loaded without lock-out occurring. 
     Once the program product has been accepted the interface  60  will flash a message “LOAD PRODUCT”. Once loaded, the baker presses the “BAKE START” button, and the elements are thermostatically operated by power source  63  to maintain the trip temperature. 
     As heat is supplied directly to the product from elements on the oven floor and oven roof, it is possible to provide more or less top heat or bottom heat to the product, so as to ensure that, for example, product with a thicker bottom material than top material will have the thicker material bake at the same time by simply increasing bottom element power and reducing top element power. 
     The concentration of heating elements in the active region is thought to allow a more directed application of heat to the baking trays, thereby reducing product burning as a result of excessive oven temperature. The relative motion of the carousel has been found to reduce burning of products overlying the elements. 
     It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Technology Classification (CPC): 5