Abstract:
Meat or poultry is cooked automatically in a thermal oven to a desired degree of doneness by a chosen time. The temperature of the meat or poultry is monitored, and linear extrapolations are made therefrom. These extrapolations are compared to the course the cooking should follow, and the oven temperature is automatically varied to correct deviations from the ideal course.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to methods for cooking meat automatically, and more particularly to methods for cooking meat in a thermal oven automatically to a desired degree of doneness and finishing exactly at a selected time, by controlling the temperature of the oven being used to cook the meat. 
     It is conventional to roast meat automatically by cooking for a length of time selected by the cook. If the cook errs in estimating the weight of the roast, however, the meat will be under- or overcooked. Other variations in the meat (fat content, thickness) affect the optimum cooking time but are difficult to allow for accurately in setting the cooking time. 
     According to another well-known method, the cook selects the temperature the interior of the meat will have when the desired degree of doneness is reached. The oven automatically turns off when the meat reaches the selected temperature. Assuming that the cook knows the correct internal meat temperature for a given meat and a given doneness, the meat can be cooked as desired. The problem is that variations in the thickness and fat content of the roast cause variations in the cooking time required, as a result of which the cook can not predict accurately when the meat will be done. 
     A third well-known method, suitable for use only with microwave ovens, is to cook the meat to the desired doneness and then to reduce the rate of energy input to a meat to a level just sufficient to keep the meat at the desired temperature, without cooking it further. In this method, the doneness of the meat is measured by its internal temperature. This method is inherently inapplicable to thermal ovens. 
     SUMMARY OF THE INVENTION 
     The principal object of the present invention is to provide a method for cooking meat automatically to the desired doneness, and finishing exactly at a pre-selected time. 
     Another object is to provide such a method that will satisfactorily compensate for large variations in the consistency of the meat and that is highly tolerant of error in the cook&#39;s estimate of the roast weight. 
     According to the method of the invention, the cooking time of the meat is divided into three parts: a warm-up period; a linear period, during which the internal temperature of the meat increases approximately linearly with time; and an end period. The meat&#39;s internal temperature is monitored, and during the linear and end periods it is compared to a pre-determined standard that is a function of cooking time elapsed, of the type of meat and of the weight of the roast. Whenever it is cooking too fast or too slowly, the oven temperature is lowered or raised. The compensation is of an amount calculated to ensure that by the cessation of the end period, the meat will be within a certain number of degrees of the desired final temperature. During the end period, the meat temperature increases more gradually than in the linear period, &#34;coasting&#34; to the desired value at or slightly before the set finishing time. In addition, it is possible to sear the exterior of the meat during this period. 
     In order to simplify the cooking process, only three oven temperatures are used. The three temperatures chosen depend on the meat. For example, the temperatures used with beef are 200° F., 325° F., and 375° F. 375° F. appears to be the highest temperature that can be used conveniently and safely for cooking meat without running the risk of setting the grease in the oven on fire. For cooking poultry, however, higher temperatures can be used. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     The embodiment described and illustrated in the following is by way of illustration only and does not in any way limit the scope of the invention. 
     FIG. 1 is a graph of meat temperature versus cooking time elapsed, showing the division of the process into three phases. 
     FIG. 2 is a graph similar to that of FIG. 1, showing the E-point and the H-lines (defined below), which are the standards by which the progress of the cooking of a given roast is increased, and showing several possible cooking curves for a roast. 
     FIGS. 3A-3B are flow-charts indicating the steps of the method of the present invention; and 
     FIGS. 4A-4F illustrate a flow-chart showing the steps of the method of the invention as they may be carried out in the preferred manner, i.e. by means of a programmed microprocessor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As stated above in the summary of the invention and as shown in FIG. 1, the cooking process is divided into three phases. During a large portion of the cooking process, the interior temperature of the meat increases approximately linearly with cooking time. This period is denoted as the linear period, and is the second of the three phases of the cooking process. The warm-up period, which is phase one of the process, is the time before the beginning of the linear period. The end phase, phase three, comprises the remainder of the cooking process. It has been found that the linear phase begins when the interior temperature of the meat has risen approximately twenty Fahrenheit degrees above its original temperature. The cooking proceeds during the first phase in a highly variable fashion dependent upon the pecularities of the piece of meat being cooked. For this reason, no action is taken during this phase other than normal cooking. 
     For the purposes of the present invention, the linear phase is defined as starting at whatever time the temperature of the meat reaches twenty Fahrenheit degrees above its original temperature and ending after seventy percent of the total cooking time has elapsed. It has been found that during the linear period the rate of cooking as measured by the interior temperature of the roast remains fairly constant. Because of this fact it is possible to measure the interior temperature at two different times during this phase and to make a linear projection of the interior temperature of the meat at the end of the linear phase. This allows us to determine whether the meat is cooking too fast or too slowly. Depending on the projection, the oven temperature can be raised or lowered. 
     The standards according to which the cooking speed of the meat is judged either too fast or too slow during the linear phase are shown graphically in FIG. 2 as point E and line H1. Point E is a point through which the ideal cooking curve of a roast will pass. If the roast attains the temperature corresponding to point E at the time corresponding to point E and the oven is then turned down relatively low, the roast will reach the desired internal temperature at the desired time. Point E was empirically found to correspond to a temperature some 35-45 Fahrenheit degrees below the desired done temperature and to the lapse of 70 percent of the cooking time. 
     It has been found that the results are improved significantly if the difference between the temperature corresponding to point E and the target temperature is varied depending on the target temperature. For target temperatures below 140° F., it has been found that the optimum temperature at point E is 45 Fahrenheit degrees below the target temperature; for target temperatures 160° Fahrenheit or above, the optimum difference is 35 Fahrenheit degrees; and for other target temperatures the optimum difference is 40 Fahrenheit degrees. 
     Line H1 is the line having a slope of 1 Fahrenheit degree per four minutes and passing through point E. It has been found that if the meat is cooking too fast, as illustrated by the examples of curves B and C in FIG. 2, then if the oven temperature is lowered sufficiently at the time corresponding to the intersection of the cooking curve with the line H1 (points X and Y), the amount by which the temperature of the meat must yet rise to attain the done temperature is such as to ensure that the meat will reach the done temperature at the appointed time. It is accordingly unnecessary to turn down the oven temperature when the linear projection indicates that the meat is cooking too fast, until the cooking curve reaches line H1. It is necessary however, to increase cooking temperature prior to this time if a projection of the meat temperature at the time corresponding to point E (this projection is described infra) is too low. In such a case, the cooking temperature is raised until further projections indicate that the meat temperature at point E will be satisfactory or until the line H1 is reached. 
     The final phase consists of the last thirty percent of the cooking time. In this phase the slope of the cooking curve falls from its maximum value, which is normally reached when the cooking curve crosses the line H1 during the linear phase, to a final approach value, and any final corrections necessary to ensure that the proper interior meat temperature will in fact be attained are performed. During this phase the oven temperature is normally set to the lowest of three settings used in the cooking process for a given type of meat. 
     During the final phase the rate of change of the cooking curve, i.e. the rate of deceleration of the cooking speed, is monitored. If the deceleration is too rapid, the oven will be turned up from its lowest setting to an intermediate setting until the rate of deceleration has decreased acceptably, after which the oven temperature may be turned back down. Similarly, if the final approach slope is below the expected value, the oven temperature is turned up to its intermediate value. If at any time during the end phase the cooking curve falls below line H2 (see FIG. 2), the oven temperature is turned up to the highest of the three settings used for the type of meat being cooked. Line H2 is the line segment connecting point E and the target point T. 
     In order to make the roast more appealing, it is possible to sear it during the last few minutes of the end phase. During the searing, the temperature of the oven is turned to its highest value. The time required for searing has been found to be a number of minutes equal to 7 plus the weight of the roast in pounds. 
     A detailed description of a preferred version of the process of the invention, illustrated in the flow chart of FIG. 3, follows. 
     The type and weight of the meat, the final internal temperature of the meat corresponding to the desired degree of doneness, and the desired finishing time are used to determine the required cooking time and the time at which cooking should start. (Alternatively, the starting time can be selected by the cook and the finishing time computed). From these figures the time and temperature corresponding to point E, and lines H1 and H2, can be computed in accordance with their above definitions. It should be reiterated that the temperature difference between point E and the done temperature will itself depend on the done temperature, varying from 35° F. to 45° F. The data needed to perform these steps, viz. the internal temperatures corresponding to different degrees of doneness and the proper cooking times for roasts of different sizes and meats, can be summarized in tables (see Table 1 of the Appendix). It may be especially convenient, as will be described below, to express cooking times for different meats as percentages of the cooking time of a roast of beef of the same size. 
     Cooking begins with the oven turned to the intermediate (T2) of the three temperatures (T1, T2, T3) at which it will be used with a given type of meat. (Hereinafter beef will be used as an example, the three oven temperatures for which may conveniently, but need not, be 200° F., 325° F. and 375° F.) The initial temperature of the interior of the meat is read, for example by means of a meat probe thermometer. (The internal meat temperature will hereinafter be designated Tm.) This is reread at short intervals and the readings compared to the original internal temperature. When Tm has risen 20° F. above its original value, the meat is considered to have entered the second, or linear, phase of cooking. 
     From the onset of the linear phase, Tm is measured periodically. The interval V between readings is preferably a number of minutes equal to the weight of the meat in pounds plus two, so that Tm is checked reasonably but not unnecessarily frequently. These measurements continue until the time corresponding to point E is reached or until Tm becomes greater than the ordinate of line H1 corresponding to the time of the reading. If the cooking curve does cross H1, the oven temperature can be turned down to its lowest setting T1, and the meat will &#34;coast&#34; to approximately the desired done temperature at approximately the correct time (H1, as noted above, is designed to make this the case). Accordingly, in this case the oven is turned down to T1, where it is held until 70% of the cooking time has elapsed. 
     Until either the E-point time is reached or line H1 is crossed, Tm is periodically measured, and a linear projection of the value Tm will have at the E-point time is made after each new reading of Tm. Each linear projection is made according to the equation 
     
         T.sub.lin proj =Tm2+[(Tm2-Tm1) ×(E-point time-Now)/(W+1)](1) 
    
     where T lin  proj is the projected temperature, Tm2 is the last reading of Tm, Tm1 is the preceding reading of Tm, &#34;Now&#34; is the time of the latest Tm reading, and W is the interval in minutes between consecutive readings of Tm. As explained above, the ideal cooking curve passes through point E. Because of this, and because it is preferable in this phase to cook too fast rather than too slow (the cooking can be slowed down nearly to a halt in the end phase but cannot be accelerated beyond a certain point), if the projected temperature is not greater than the temperature corresponding to point E, the oven temperature is turned to the maximum setting T3, 375° F. in the case of beef, unless it is already at T3. If the projected temperature is greater than the E-point temperature, the meat is cooking too fast. The oven will be turned to T2 in this case if it is at its highest setting T3. Since, as stated above, it is preferable to cook too fast rather than too slow, the oven temperature will be lowered to T2 only if two consecutive linear projections are low. 
     When the E-point time is reached, Tm is measured twice more, at the interval W used in the linear phase between readings. These two new readings are used to make a linear projection of the final meat temperature. This projection follows the equation given above in connection with the linear projection of the linear phase, with E-point time replaced by the finish time. The projected final temperature is compared to the desired done temperature (TD hereinafter). The next portion of the process can be any one of several sequences. 
     First, if the projected temperature is less than than or equal to TD, the oven temperature is set at T2, if it is not already there. Then the actual temperature of the meat Tm is compared to the ordinate of line H2 for the time of the reading of Tm. If the cooking curve is above line H2, then this portion of the process is complete. If on the other hand the cooking curve is not above line H2, the oven setting is turned up to the maximum setting T3, and this portion is complete. 
     If the projected final temperature is greater than TD, this is an indication that the cooking is proceeding too fast, and the oven temperature is turned down to its lowest setting T1, if it is not already there. 
     If the projected final temperature does exceed TD, but does not exceed the preceding projection, a second order projection of the final temperature Fproj is made according to the equation: 
     
         Fproj=Nproj-[((Done time-Now)/W)×(Oproj-Nproj)]      (2) 
    
     Nproj is the most recent linear projection of the final temperature and Oproj is the preceding linear approximation thereof. If this second order approximation is at least as great as TD, then the oven temperature is turned down to its minimum setting T1 and this sequence is complete. If the second order approximation is less than or equal to TD, however, this is an indication that the cooking process is proceeding too slowly, and the oven temperature is accordingly set at its intermediate value T2, 325° F. in the case of beef. The oven temperature is moved to T2, however, only if this is the second time in a row that a second order approximation of the final temperature has been made and found to be less than TD. At this point, this portion of the procedure is complete. 
     At the conclusion of the portion of the procedure beginning with the comparison of the linear projection of the final meat temperature Tm with TD and described in the preceding paragraphs, and after a further interval W the time is checked to determine whether sear time has been reached. (As explained above, sear time is the beginning of a period at the very end of the cooking process intended to permit the exterior of the roast to be seared just prior to completion.) 
     If the sear time has not been reached, as described above, the meat temperature Tm is reread and compared to TD. If Tm has reached TD, the oven is turned off, as the cooking is done; otherwise a new linear projection of the final temperature is prepared, using the most recent value of Tm 
     When the sear time is reached, then the oven is raised to its highest setting T3 if it is not already there, provided that TM is at least 3° F. below TD. This results in the searing of the exterior of the roast for the last few minutes before the done time is reached. 
     Although the procedure described above can be carried out in any way desired, the preferred method of implementation employs a programmed microprocessor to control the thermal oven. The appropriate function code, along with the estimated weight of the roast and either the time at which the roast is to be done or the time the cook desires the cooking process to start, are all inputs provided to the microprocessor by the cook. FIGS. 4A-4F illustrate a flow chart showing the manner of implementation of the present invention by means of such a microprocessor controlled oven. 
     The oven is provided with a number of function word inputs, such as on, off, auto-roast, normal, etc. In step A1 (FIG. 4A), the microprocessor reads the function word to determine whether it is auto-roast or not (A2). If not, it waits ten seconds (A3) and then reads the function word again. When it reads the function word auto-roast, it reads the stop time which is input by the cook. At this point, two sequences of steps can occur, depending on whether the start time or the stop time has been input. The microprocessor checks to see whether a stop time has been input (A5). If it has been input, the microprocessor reads the estimated meat weight and reads the 3-digit code (described below) indicating the desired final temperature (B1). The microprocessor then computes the cook time and sets the cook time (CD1). The start time, which is equal to the done time minus the cooking time, is then calculated along with the E-point time and temperature (CD3,E). If, however, the microprocessor does not determine that a stop time has been input (A5), it reads the start time (A6) and sets it (B2). It then reads the meat weight and the 3-digit code (B1), and computes and sets the cook time (CD1) and calculates the down time, which is equal to the start time plus the cooked time (CD2). It then calculates the time and temperature corresponding to point E (step E). 
     After calculating the E point time and temperature, the microprocessor sets the stop time or the start time (FIG. 4B), as the case may be, and displays the start time, the done time and the meat temperature for the cook to see (EF). At ten second intervals, the microprocessor checks to determine whether it is yet the start time (G1). When start time is reached, the oven is set to an intermediate temperature (MID TEMP), e.g. 325° F. in the case of beef, and the meat temperature is read (H1). The most recent reading of the meat temperature is then stored, and the temperature is read again (H2). If the new temperature is not 20° F. more than the old temperature (I1), then after a one minute waiting period (I2), a new rending is taken (H2). When the new temperature finally rises 20° F. above the original temperature, the microprocessor computes W, which is a number of minutes equal to the weight of the meat in pounds plus the two (J). The variable N Temp, which is equal to the current temperature of the meat, is set (K1). The variable O Temp is set equal to N Temp (K2), and after waiting one time period W (L1), the time is read (L2). The microprocessor checks to determine whether we are past the time corresponding to point E (L3) (See FIG. 4C). If so, the microprocessor goes immediately to step P (described below). If not, it checks to determine whether the cooking curve is above the line H1 (M1). If so, the oven temperature is set to its lowest setting (LO TEMP., e.g. 200° F. (M2), and nothing more is done until the time corresponding-to point E has been reached (M3), at which time the microprocessor goes directly to step P. 
     If the microprocessor determines that the cooking curve has not crossed line H1, it makes the linear projection from the current time to the E-point time in accordance with equation (1), supra, (N1), and compares the projection with the E-point temperature. If the projection is less than or equal to the E-point temperature, the oven is turned up to its highest setting (e.g. 375° F.) (N3), and the microprocessor returns to step K1. If the linear projection is greater than the E-point temperature, the microprocessor checks to determine whether the oven is set at the highest temperature (HI TEMP) of 375° F. (01). If not, it returns to step K1. If the oven is at its highest setting, the microprocessor determines whether the most recent linear projection is the second consecutive linear projection greater than the E-point temperature (02). If so, it sets the oven temperature to its intermediate (MID TEMP) value of e.g. 325° F. (04), and proceeds to step K1. If not, this linear projection is counted (03), so that when the next linear projection is made the microprocessor will be able to determine whether it is the second consecutive high projection. Then the microprocessor goes back to step K1 (FIG. 4B). 
     When step P (FIG. 4D) is reached as described above, we are beginning the final phase. At this point, it is necessary to reinitialize the count register which is used to count the number of consecutive linear approximations made using equation (2), and to place the current temperature into the 0 temp register (P). After one timed period W (Q1), the temperature of the meat is reread and stored in the N Temp register and the time is read (Q2). A linear projection is then made of the final temperature, in accordance with equation (2), supra, (R1). The projected final temperature is then compared to the desired done temperature TD (R2). If the current linear projection is greater than TD, then the current linear projection is compared to its predecessor (T1). If the earlier projection is greater than the current linear projection, then the microprocessor proceeds to step U1 (described below). If the current linear projection is at least as great as its predecessor, then the microprocessor checks to see whether the oven is at its lowest (LO TEMP.) setting (e.g. 200° F.) (V1). If it is, the 0 Temp register is set to the value previously contained in the N Temp resister, and similarly, the register Oproj is given the value of the Nproj register, which contains the value of the most recent linear projection of the final temperature (W). If the microprocessor has discovered in step V1 that the oven is not set at its lowest setting, the oven is then set to that temperature (T2), after which registered 0 Temp and Oproj are reset as described above (W). If in step R2, the linear projection is found not to be greater than TD, then the oven temperature is set to its middle (MID TEMP.) setting (e.g. 325° F.) (R3), and the microprocessor checks to determine whether the cooking curve is above line H2 (V2). If it has, we go directly to step W; if not, then the oven temperature is set to its highest setting (e.g 375° F.) (V3), and then we go to step W. 
     As described above, if Oproj is found to be greater than the most recent linear projection in step T1, the microprocessor goes to step U1 (FIG. 4F), in which the second order approximation of the done temperature is made in accordance with equation (3), supra, and is compared to TD. If the second order projection Fproj is greater than or equal to TD, the oven temperature is set to its lowest setting and the count is set to zero (U3), and we go to step W (FIG. 4D). If the second order projection is less than TD, then the microprocessor checks to determine whether this is the second consecutive second order projection less than TD (U2). If it is, the oven temperature is set to its intermediate setting (U4), and we go to step W. If this is not the second consecutive low second order projection, this projection is counted (U5), so that the microprocessor will be able to determine whether the next second order approximation is the second consecutive low one or not. From step U5 we go, again, to step W. 
     From step W, in which the O Temp and Oproj registers are reset, after waiting one timed period W (X), the microprocessor checks to determine whether we are past sear time or not (Y1) (see FIG. 4E). If so, the oven is checked to determine whether it is set to its highest level (Y2). If it is, the microprocessor proceeds to step Z1 (described below). If the oven is not at its highest setting, the microprocessor checks to determine whether the meat temperature is at least as high as TD-3° F. (Y3). If it is, we proceed directly to step Z1. If not, the oven temperature is set up to its highest setting (Y4), after which the microprocessor checks to determine whether done time has been reached (Z1). If it is, the cooking process is ended (Z3). If not, the microprocessor waits ten seconds (Z2) and checks the time again (Z1). If the microprocessor determines in step Y1 that sear time has not been reached, then it reads meat temperature (Y5) and compares it to the done temperature TD (Y6). If the meat temperature is above the done temperature, the oven is turned off (Y7) and the microprocessor goes to step Z1 (described above). If the done temperature has not been reached, the microprocessor returns to step Q2 to begin the process of making another linear approximation. 
     When carrying out the foregoing procedure, the user positions a meat probe thermometer approximately in the center of the roast, and inputs the necessary data, namely the type and weight of the meat, the desired final temperature of the meat, and the desired done time. When doing so, it is preferable to input the cooking time percentage and the desired final temperature using a 3-digit code. The user inputs a 3-digit number: the first digit indicates the cooking time for the type of meat presently being cooked, expressed as a percentage of the cooking time that would be required for a rolled rib beef roast of the same weight, while the last two digits indicate the desired final temperature. The cooking time percentage is indicated as follows: Zero indicates that the cooking time should be the same as that for beef, 1 indicates ninety percent as long as for a beef roast of the same weight, 2 indicates eighty percent, etc. For various types of meat, the digits 0-5 will suffice, while digits 6-9 will be suitable for use with poultry. The last two digits of the code are the last two digits of the desired final temperature in Fahrenheit degrees, the first digit of which is assumed to be 1. It has been found that this simple and convenient 3-digit code significantly simplifies and reduces the expense of the electronic circuitry required to implement the invention. 
     Although one preferred embodiment of the method of the present invention has been described in detail above, this is given by way of example only, and accordingly, the scope of the present invention is to be limited not by the details of the foregoing description but only by the terms of the appended claims. 
     APPENDIX 
     
                       TABLE 1______________________________________Type of Meat  % Cook Time Code   Temp. Range______________________________________BEEFRolled Rib    100         0      125-165(Boneless)Standing Rib  80          2      125-165(Bone-In)VEALRolled Rib    100         0      125-165(Boneless)Standing Rib  80          2      125-165(Bone-In)PORKBoston Butt,  80          2      165-185Shoulder, FreshHam (Boneless),Center LoinCenter Loin, Fresh         70          3      165-185Ham, Shoulder (Bone-In)LAMBAll types (Boneless)         70          3      135-165All types (Bone-In)         60          4      135-165______________________________________ 
    
     Column 2 gives the cooking time for the meat of column 1 as a percentage of the cooking time for a boneless rolled rib roast. 
     Column 3 gives the code digit containing the cooking time, as explained supra. 
     Column 4 gives the range of internal temperatures appropriate for use as target temperatures for the meats of column 1.