COMBINATION PRESS AND OVEN

Abstract: A press and oven combination for pressing and baking food products, such as tortillas, has a continuous and very thin press belt (40) moving through a press (60) and an oven (30). Heater platens (62, 64) under the press belt (40) heat the pressed tortillas primarily by conduction. By avoiding transfer of the tortillas between belts as they move from the press (60) to the oven (30) sticky or crumbly food materials may be pressed and baked. The continuous belt surface provides a griddle-like heating more similar to traditional hand made tortillas.

Description: DESCRIPTION Combination Press and Oven This application is a continuation-in-part of our Application No. 08/348,575, filed December 2, 1994 and now pending. Serial No. 08/348,575 is incorporated herein by reference. Background of Invention The field of the invention is presses and toasters (or ovens) . Various presses and ovens have been used in the past for pressing and baking food products. Forming or pressing is accomplished by loading dough balls (scoops, drops, etc., of food product) onto a press conveyor belt which moves the dough balls in batches into a press. The belt stops and the press moves to flatten the dough balls. The forming of the dough balls into disks is primarily influenced by three factors: pressing platen heat, pressing pressure and pressing dwell time. Heat is applied to overcome the "memory" of the dough (specifically flour dough) and assist in release from the transport belt. Pressure is applied to further overcome the resistance of the dough. Pressing time must be sufficient to allow the heat and pressure to accomplish their functions. There is a limit to the amount of heat that can be applied without degrading the quality of the processed food products. If excessive heat is used in the forming process the flattened dough pieces tend to be misshaped. Excessive heat also contributes to the loss of cell structure formed during mixing and leavening processes resulting in the formation of translucent spots. These spots result in an undesirable "raw" appearance in the finished product. For this reason, press platen temperatures rarely exceed 425 F. After the forming operation, the product must be quickly subjected to significantly higher temperatures,typically more than 500 F, to achieve desirable toast marks. This is historically accomplished by transferring product to a second transport belt that is preheated. Conventional press transport belts generally cannot be heated quickly enough (bake dwell of approximately 10-15 seconds) to achieve desired toast marks on the product, due to the large mass of the belt. Transferring the product to a second transport belt avoids this difficulty, but also introduces other disadvantages, relating e.g., to release, transfer, space requirements, etc. Generally, the second transport belts or oven belts are made of slats attached together or of a woven metal fabric. Due to the discontinuous belt surface with slat belts, "slat lines" are formed on the food product. The slat lines reflect uneven baking of the food product, and create an appearance which may be less desirable. Similarly, woven belts result in a mesh pattern on the food product, as the contact between the links of the woven belt and food product is not continuous. Traditional tortillas are made by hand and are typically cooked on a flat continuous pan or griddle and have pan cooked characteristics. Machine produced tortillas, having been baked on a slat or mesh belt, are noticeably different from the traditional product. Thus, with tortillas, and perhaps other products, there remains a need for automatically making more traditional-like product. Accordingly, it is an object of the invention to provide an improved combination press and toaster or oven. It is a further object of the invention to provide a combination press and oven for efficiently producing more traditional tortillas or other food products. Summary of the Invention To these ends, an apparatus for pressing and toasting a food product includes a continuous press belt of low mass that is capable of rapidly assimilating to the temperature of a heating platen. Preferably, the apparatus includes a press comprised of two thermostatically controlled platens, and a toasting zone comprised of an additional heated platen spaced apart from the press and positioned between the belt. The use of a low mass belt that quickly assimilates to the temperature of heated platens allows the forming and toasting operations to be done at distinctly different temperatures with the temperature transition occurring very quickly and efficiently. Brief Description of the Drawings In the drawing, wherein similar reference characters denote similar elements throughout the several views: Fig. 1 is a front elevation view of the present press and oven; Fig. 2 is a left side elevation view thereof; Fig. 3 is a rear elevation view thereof; Fig. 4 is a right side elevation view thereof; and Fig. 5 is a plan view thereof. Detailed Description of the Drawings Turning now in detail to the drawings, as shown in Figs. 1-5, the present combination press and oven 10 has a frame or housing 12 with legs 14. Referring specifically to Fig. 1, the housing 12 has a proofing cabinet or space 16, for receiving and storing a proofing cart 76. As shown in Figs. 1 and 2, a shelf 18 within the housing 12 has a projecting loading station 20. The upper section of the housing 12 is enclosed by a front panel 24, side panels 26 and ear panel 28, which are advantageously transparent, windows or doors. At the sides of the housing 12 are lower panels 32, preferably having louvers or ventilation openings, and enclosing a utility section 34. A control panel 36 is provided on the right side lower panel, for controlling and monitoring power supplies, motors, hydraulic systems, etc., as are well known in the art. Referring to Fig. 2, a press belt 40 extends substantially the entire length of the housing 12, and is supported by front and rear rollers 48 and by idlers 50. The press belt 40 is preferably of a low mass and able to rapidly change temperature. The belt 40 passes over heated platens 52, in different temperature zones. Preferably, the press belt 40 comprises thermoplastic, e.g., Teflon, coated fiberglass weave of a thickness not more than 0.012 inch and most desirably from about 0.003 to 0.005 inches thick or a sheet metal belt (preferably steel) not more than 0.040 (most desirably about 0.010) inch thick. The belt 40 advantageously has a continuous surface (without mesh or slat openings) provided by the thermoplastic, or by the sheet metal surface. Various other materials may also be used for the belt 40, for example other high temperature fabrics. The belt material should have a high elastic modulus, to resist stretching. While high thermal conductivity is advantageous low thermal conductivity materials, (like Teflon coated fiber glass) can perform well, due to the very thin belt cross section. A low specific heat material is also desirable, but not essential due to the thin cross section, and so long as the belt can change temperature quickly. As the belt is thin, small diameter end rollers can be used, reducing space requirements and energy consumption. Preferably, the end rollers have a diameter of 3-6 inches. This small diameter also can improve transfer characteristics (when used in a stand alone press or oven) as the drop distance to a second conveyor belt is reduced, correspondingly reducing the potential for the food product to fold or overlap during transfer or to land out of position. As the belt 40 is very thin, it has low mass and can heat up and cool down quickly, as it moves around between the pressing and baking/toasting sections. The membrane- like belt 40 need not be independently or externally cooled, i.e., no air blowers, water cooling, etc. is needed. The low weight of the belt reduces cost, energy use and space requirements. Heated platens 52 are positioned in the oven section 30 of the housing 12, below the advancing or top size press belt 40. The bottom of the advancing side of the press belt 40 slides over the heated platens 52. On the return side, the bottom (inside) of the press belt passes below the heated platens. As the platens are stationary, measuring and controlling temperature is simplified, in contrast to apparatus having moving heated surfaces. The platens are preferably heated by electrical strip heaters, which can be accurately controlled for proper toasting, and to avoid overheating the press belt 40. In addition, use of electrical heaters allows the combination press and oven 10 to be a substantially self-contained unit which can be installed in a compact space, e.g., in a restaurant, and requiring only electric power, with no natural gas piping or exhaust ducts required. An upper belt 42 is supported on rollers 48 and idlers 50, below the press belt 40 in the oven section 30. Similarly, a lower belt 44 is supported and positioned below the upper belt 42. A loading belt 46 supported on rollers 48 extends from the back of the housing to a drop position 45 beyond the front panel 24 and over the loading station 20. Curved end guides 54 are positioned to guide the food product as it moves downwardly through the oven section 30, from one belt to the next. Referring still to Fig. 2, a press 60 is located in a press section 58 of the housing 12. The press has an upper press platen 62 which periodically presses against a lower press platen 64. The upper and lower press platens are heated. The lower platen is positioned between the advancing and returning sides of the press belt. The advancing side slides over the lower platen 64 as the press belt advances. In use, the press and oven combination 10, being a relatively compact and self-contained unit, may be installed in a restaurant or other location where the working components and tortilla making operation can be seen by the public or customers. The proofing tray cart 76, carrying trays 72 of doughballs 66 is wheeled into the cart storage space 16. The operator removes a tray 72 and places it on a tray shelf 74, at the front of the housing 12 below the press 60. The doughballs 66 are removed from the tray 74 and placed onto the press belt 40 through a loading slot or opening 70 in the front panel 24. Controls in the utility section 34 automatically stepwise advance the press belt 40 and operate the press 60. A single doughball 66 is moved under the platen 62 and is flattened when the press 60 is actuated. In a preferred embodiment, the platen 62 is approximately a 10 inch square, and the doughballs 66 sized to flatten to a nine inch diameter tortilla. Referring to Fig. 5, as the press belt 40 advances, a series of tortillas are made, typically at a rate of about one every three seconds. Tortillas 68 on the press belt 40 move into the oven section 30 while remaining on the press belt 40. Heat from the heaters 52 passes primarily via conduction through the press belt 40 to heat the tortillas 68. While the air in the oven section 30 is also heated and provides some convection heating, the tortillas are primarily heated via conduction through the press belt 40. When the tortillas reach the back end 38 of the press belt 40, they are already partially baked. As a result of the release characteristics of the pres belt 40, and of being partially baked, the tortillas 68 fall freely off of the press belt 40 onto the upper belt 42 moving in the opposite direction (as indicated by the arrow in Fig. 2) . The end guide 54 helps to direct the falling tortilla 68 from the press belt 40 onto the upper belt 42. As the tortillas 68 move on the upper belt 42 they continue to be heated and baked, primarily by conduction from the heaters 52 underneath the upper belt 42. When the tortilla 68 reach the end of the upper belt 42, they fall onto the lower belt 44, guided by the end guide 54, and continue to be heated as they move again towards the back of the oven section 30 on the lower belt 44. At the back 56 of the lower belt 46, the tortillas 68 fall onto the loading belt 46 and move towards the front of the housing 12, while cooling. At the front of the loading belt 46, the tortillas 68 fall into a basket 22 placed on the loading station 20. The basket 22 containing the freshly cooked tortillas can then be carried directly to tables. Additional baskets 22 are stored on the shelf 18. The doughballs and baskets may be placed by hand. A significant advantage of the press and oven combination 10, using a low mass belt, is that certain food products tend to stick to a press or oven belt, especially after being pressed and flattened onto the belt. However, as shown in Fig. 2, because the press belt 40 carries the tortillas (or other food product) into the oven section, and is quickly heated, (the transition from the press temperature to toasting temperature is accomplished in a few seconds) , the tendency to stick to the belt is largely overcome without sacrifice of throughput or quality. By the time the tortillas 68 reach the back 38 of the press belt 40 they are sufficiently baked so that they readily release from the belt 40. The continuity of the press belt 40 through the press 60 and the oven section 30 also allows the combination press and oven 10 to make pressed corn tortillas. Pressing instead of sheeting corn tortillas is advantageous as it reduces waste. Moreover, pressed corn tortillas have a different quality from corn tortillas made by sheeting. In conventional presses and ovens, corn tortillas are not readily pressed and baked, due to difficulties in transferring the pressed corn tortilla from a press belt to an oven belt. During such transfer, the corn tortilla (having been pressed, but not baked) tends to stick too much to the press belt which defeats transfer. Thus, presently corn tortillas are only made automatically by "sheeting" or die cutting from a rolled flat sheet of corn product. The present press and oven combination 10 avoids transfer between pressing and baking. Thus, pressed corn tortillas can be automatically made. The pressed corn tortillas are partially baked in the oven section 30, while still supported on the press belt 40. While baking on the press belt could in principle be carried out, this would require a very long press cycle and would not be useful. When pressing corn tortillas, the platen 62 is provided with a thickness gauge switch which when engaged, stops the press 60 at a certain gap between the upper platen 62 and lower platen 64, to accommodate the clay¬ like texture of corn, whereas with other products, such as flour tortillas, the press 60 continues to press until a certain pressure (rather than a certain gap distance) is reached. Pressed corn tortillas, which the invention now makes commercially available, have qualities different from the sheeted corn tortillas. The press belt 40 has a flat and continuous or smooth surface. Thus tortillas or other products are produced without slat lines, weave patterns, or other marks or characteristics. Accordingly, a more flat griddle hand made-lie product is obtained. Advantages of the press belt 40, e.g., quick heating and cooling, reduced energy use, griddle like heating surface, can, of course, be realized also by using the belt 40 in a stand-above oven or toaster, operating apart or without a press. Thus, a novel combination press and oven, and press belt have been shown and described. Many changes and modifications may of course be made without departing from the spirit and scope of the invention. The invention, therefore, should not be restricted, except as described in the following claims.

Claims: Claims 1. An apparatus for pressing and heating a food product, comprising: a press; a press belt passing through the press, the press belt having a continuous surface; and a heater platen spaced apart from the press and positioned between the belt. 2. The apparatus of claim 1 wherein the belt comprises a woven material having a thickness less than 0.012 inches. 3. The apparatus of claim 1 wherein the belt comprises sheet metal having a thickness less than 0.040 inches. 4. The apparatus of claim 1 wherein the belt has a mass per unit length and a specific heat to allow the belt to cool by at least 75°F, in one rotation of the belt, without external cooling. 5. The apparatus of claim 1 wherein the belt comprises Teflon coated fiberglass and has a thickness of about 0.003-0.005 inches. 6. The apparatus of claim 1 further comprising end rollers supporting the press belt, with the end rollers having a diameter of approximately 3-6 inches. 7. The apparatus of claim 3 wherein the belt thickness is about 0.010 inch. 8. An oven/press combination comprising: a housing; a press supported within the housing: a continuous membrane-like press belt supported on spaced apart rollers substantially within the housing; and a press belt heater within the housing positioned so that the press belt passes around the heater. 9. The oven/press combination of claim 8 wherein the press belt has an advancing side and a return side, and wherein a section of the advancing side make sliding contact with the press belt heater. 10. The oven/press combination of claim 8 further comprising a loading belt below the press belt, with the loading belt having a first end for receiving food product, adjacent to a rear panel of the oven/press combination, and having a second end, for delivering food product out of the oven/press combination, adjacent to front panel. 11. The oven/press combination of claim 10 wherein the second end of the loading belt extends out of the housing. 12. The oven/press combination of claim 11 further comprising: an upper belt between the press belt and the loading belt; a lower belt between the upper belt and the loading belt; an upper belt heater associated with the upper belt; and a lower belt heater associated with the lower belt.

Inventors: LAWRENCE ERIC C, MERRIL JAMES, LAWRENCE, ERIC, C., MERRIL, JAMES
Applicants: LAWRENCE EQUIP INC, LAWRENCE EQUIPMENT, INC.
Application year: 1995
Main classification: A47J37
IPC codes: A21B1, A47J37