WO2005074725A1

WO2005074725A1 - Method and system for producing a food product

Info

Publication number: WO2005074725A1
Application number: PCT/AU2005/000122
Authority: WO
Inventors: Raymond Michael Morgan
Original assignee: Microlock Corporation Limited
Priority date: 2004-02-03
Filing date: 2005-02-01
Publication date: 2005-08-18

Abstract

The present invention concerns a method and system of sterilizing a food product using thermistor probes to accurately monitor the temperature of the food product during sterilisation in a retort and following a predetermined heat curve for the food product type to achieve sterilization in order to maintain maximum product integrity.

Description

METHOD AND SYSTEM FOR PRODUCING A FOOD PRODUCT

FIELD OF INVENTION The present invention relates to a method of producing a substantially sterilized food product. The present invention has particular but not exclusive application to the packaging and sterilizing of cooked food products.

PRIOR ART Processed foods generally spoil over time. Microbes decompose food and produce toxic compounds. When humans eat the spoiled or contaminated food they can become ill and even die. To extend the shelf life of processed foods, two approaches have been developed. Microbial growth has been slowed or inhibited employing methods such as freezing, refrigeration, drying and adding preservatives to the processed foods. Processed foods have also been sterilized with heat pressure treatments, irradiation and pasteurization. Heat pressure sterilization includes retort processing which sterilizes the processed food in the container and aseptic processing which sterilizes the processed food prior to placement in the container. With retort processing, food products are first filled and hermetically sealed in pouches, cans, jars, or other retortable containers, then heated in their containers using hot steam or water under pressure so that heat penetrates the product from the container wall inwardly and both product and can wall become sterilized together. Retorts which are large industrial-sized autoclave-type vessels use thermocouples to measure temperature. Thermocouples have an operating range of -200°C to +400°C +/- 3°C. While thermocouples have a relatively wide operating range, they have a relatively poor accuracy which consequently requires the food products to be treated for an extended period in the retort at high temperature and pressure to take into account the possible temperature variation. As a consequence the food product is over processed and the resultant product has degraded texture and consistency, lacks taste and decreased nutrimental value.

OBJECT OF THE INVENTION It is an object of the present invention to provide an alternative method to the sterilization of food products that overcomes at least in part one or more of the above mentioned problems.

SUMMARY OF THE INVENTION The present invention results from conceiving and developing an alternative approach in using thermistors which have a relatively narrow range of +10°C to +170°C but an accuracy of +/- 0.05°C. Though thermistors have been used to measure temperature during the sterilization of medical products, they have not been used in the food industry. The present invention results from developing the use of thermistors to the sterilization of food products and overcoming problems posed by their use. In one aspect the present invention broadly resides in a method of sterilizing a food product including positioning the food product in a retort; sterilizing the food product in accordance with predetermined temperatures, pressures and time calculated to produce a substantially sterilized food product; wherein the predetermined temperature, pressure and time is calculated for each food product type to achieve maximum product integrity. Maximum product integrity includes considerations of product texture, product consistency, product appearance, product taste and product nutritional value. A heat curve formed from the predetermined temperatures, pressures and time is preferably produced and followed for sterilization of the food product. In another aspect the present invention broadly resides in a method of sterilizing a food product including positioning the food product in a retort; sterilizing the food product in accordance with predetermined temperatures and pressures over a period of time calculated to produce a substantially sterilized food product; said temperatures are determined with one or more thermistor probes associated with the packaged food product, wherein the predetermined temperature, pressure and time is calculated for each food product type to maintain maximum product integrity. The thermistor probe is preferably positioned through the retort container or package of a sample of the food product for accurately measuring temperatures, said sterilization includes subjecting the food product to heat and pressure over a period of time in accordance with a predetermined heat curve for sterilization of the food product type thereby maintaining maximum product integrity. The abovementioned method may also include the initial step of predetermining the preferred heat curve for the particular food product. Preferably there is an initial step of determining a heat curve of the predetermined temperatures, pressures and time for sterilization of the food product type and then using the heat curve for sterilization of packages of the food product. Preferably the thermistor probe is operatively connected to a data control means for collection and analysis of the data; said operative connection includes a pressurized flange in the retort wall enabling electrical connection between the thermistor probe and the remotely located data control means. Preferably the data control means includes a processor for processing temperature, pressure and time data and operating temperature and pressure control means according to the processed data and the predetermined heat curve. The desired heat curve preferably has a comparatively lower temperature.

The desired heat curve preferably reaches the lower sterilization temperature comparatively more quickly than with conventional sterilization. For a particular food product, the desired heat curve may compromise on temperature to achieve a shorter sterilization time. The thermistor probe preferably has a pointed end to allow the probe to penetrate the food product package. The thermistor probe is preferably conical. In a further aspect the invention broadly resides in a method of determining a heat curve for the sterilization of a food product including positioning a thermistor probe through the retort container or package of the food product, sterilizing the food product while measuring the temperature of the food product and pressure within the retort and time elapsed during sterilization; assaying for viable microbial concentration; and determining whether the viable microbial concentration is acceptable for the sale of the food product. Preferably for the method of determining a heat curve for the sterilization of a food product, the thermistor is inserted into one sample of the food product while a different sample is used for the assay for viable microbial concentration. Preferably each prepared batch of a particular food product has a thermistor in a sample and a further sample may be assayed for viable microbial concentration. In another aspect the invention broadly resides in a system for sterilizing a food product using the method as claimed in any one of claims 4 to 6 including a retort; a thermistor probe insertable within a retortable container or packaged food product; electrical connection between the probe and the data control means, wherein the temperature and pressure is monitored and controlled during the sterilization process. Preferably the thermistor probe includes one or more other sensors such as a pressure sensor. In another aspect the invention broadly resides in a method of producing a food product including preparing the food product; packaging the food product; and sterilizing the food product as described above. In a further aspect the invention broadly resides in a food product prepared by the method described above. In another aspect the invention broadly resides in a method of sterilizing a food product as described above wherein water from the retort is placed in one or more containers depending on the temperature of the water and reused in the retort to shorten the time to reach sterilizing temperatures in the retort. In this way heated water is recycled thereby saving time and energy. Preferably water is sterilized before it reenters the retort. Preferably the method involves sterilizing the water being discharged from the retort and sterilizing water from said containers before it enters the retort. Food products includes raw and processed meat, fish, poultry, game and vegetable products. Vegetable products are preferably substantially sterilized by the abovementioned method and system using temperatures below 100 °C thereby substantially preserving the integrity of the product. With this method relatively large volumes of vegetable matter can be substantially sterilized prior to sealing. The method of substantially sterilizing vegetable products avoids sterilizing with acidic solutions which affects the quality and taste of the vegetable product.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the present invention be more readily understood and put into practical effect, reference will now be made to the accompanying drawings wherein: Figure 1 is a diagrammatic view of the retort and sterilization system; Figure 2 is an (a) plan and (b) side view of the retort tray; Figure 3 includes various views of the retort basket; Figure 4 is a diagrammatic view of the thermistor probe and transmission unit; Figure 5 is a diagrammatic view of the thermistor probe; Figure 6 is a schematic view of the water system for the retort; Figure 7A is a diagrammatic view of the filter system for the sterilization of water, while Figure 7B is a schematic view of the recycling water system for the retort; Figure 8 is a diagrammatic view of the sterilization process; Figure 9 is a graph comparing the sterilization process of the present invention with the current sterilization process; Figure 10 is a graph showing the temperature profile of the Korean ox-tail soup product during the sterilization process; Figure 11 is a graph of the Gillespy calculations for the Korean ox-tail soup product; Figure 12 is a table setting out the data collected from the thermistor probes for the Korean ox-tail soup product; Figure 13 is a graph showing the temperature profile of the Korean Beef Cheek soup product during the sterilization process; Figure 14 is a graph of the Gillespy calculations for the Korean Beef Cheek soup product; Figure 15 is a table setting out the data collected from the thermistor probes for the Korean Beef Cheek soup product; Figure 16 is a graph showing the temperature profile of the American Meat Ball product during the sterilization process; Figure 17 is a graph of the Gillespy calculations for the American Meat Ball product; and Figure 18 is a table setting out the data collected from the thermistor probes for the American Meat Ball product.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With respect to Figures 1, 2, 3 and 4 there is shown a retort sterilization system. The retort 10 is a large industrialized-sized autoclave vessel in which pouches of processed food placed on trays 11 which are stacked in baskets 12, are placed inside the retort 10 for sterilization of the food product. The tray 11 is shown in more detail in Figure 2. The base 13 of the tray 11 is perforated to allow steam to reach substantially all areas of the tray 11 so that steam can penetrate pouches irrespective of their position on the tray 11. The thermistor probe 22 is directly connected through the pressurized flange 19 to the data control unit 18. The electrical connection through the retort wall 20 is via a pressurized flange 19 because it allows the sterilization process to occur without loss of pressure and temperature. The data control unit 18 is connected to a

CPU 21 which collects and analyses the data. The thermistor probe 22 has a conical end 24 to allow the probe 22 to pierce the retortable pouch and insert into the food product. By way of example, each pouch containing Korean ox-tail soup product has an ox-tail bone and the thermistor probe 22 is inserted adjacent to the bone to measure, the temperature of the food product at its slowest heating point. The thermistor probe 22 has a thermistor sensor 25 adjacent to the conical end 24. The thermistor sensor 25 is electrically connected to a connection lead 27 via a rear pressure plug 28. The thermistor probe 22 is internally packed with standard packing material 29. The thermistor probe 22 has a stainless steel outer cylindrical casing 26. The water system associated with the operation of the retort 10 is shown in Figure 6. A water system which recycles water through the retort 10 is shown in Figure

7. The sterilization process involves heating water to a predetermined temperature, holding the temperature of the water at the predetermined temperature for a predetermined period, and then cooling the water so that the retort 10 can be opened and the sterilized food product removed. With recycling of water through the retort 10 there are advantages in the reduced consumption of energy for heating and cooling the water, the reduction in volume of water used and a shorter length of time required for the sterilization process. Where the sterilization process takes a relatively shorter length of time compared with non water-recycling processes, additional number of sterilization cycles may be performed thereby increasing the number of food products sterilized during an operational period. The recycling water system stores heated water from the retort 10 according to temperature in respective containers 30. Water is discharged from the retort 10 via a filter 31. Water is then stored in the appropriate container 30 for the temperature of the water or discharged to waste. When heated water is required in the retort 10, pre-heated water from the appropriate container 30 is introduced into the retort 10 via a filter 32. Filters 31 and 32 comprise single or combinations of UV sterilisation, filtering with carbon filters and sterilization with ionization units. The filters are shown in more detail in figure 7B. Water is discharged and re-introduced to the retort 10 via mixing unit controls 34, pumps 33 and staging pressure valve 35. The recycling of water is preferably independent of the introduction of fresh water and the two systems are complementary. The sterilization process includes the placement of the retortable pouch containing the food product within the retort 10 and sterilizing the food product with superheated water at a temperature and pressure that will kill bacteria to a level acceptable to government regulation standards such as the AQIS (Australian Quarantine Inspection Service) standards. The sterilization treatment preferably kills substantially all of the bacteria present in the food product. The degree of lethality is determined by the Fo value where one unit represents one minute at 121°C. For meat products, acceptable Fo values are 2.8 and above. With the accuracy in measuring the temperature with the thermistor probes 22, the food products can be sterilized at relatively lower temperatures and pressures thereby preserving the integrity of the food product. A heat curve is created for each food product type by measuring temperature, pressure and time during the sterilization process and subsequently determining viable bacterial counts from a food product pouch and calculating the F₀ value. Examples of determining the heat curve for particular food product types is provided below with Korean ox-tail soup, Korean beef cheek soup and American meatballs. The heat curve for each product food type is different. After the heat curve has been determined for the particular food product type, samples of the food product type may then be sterilized with parameters set to follow the determined heat curve. Verification that the subsequent food products have been sterilized may be determined by using the Gillespy Method as shown in the below mentioned examples. The sterilization process of a particular food product is diagrammatically shown in Figure 8. Figure 9 shows the comparison between the heat curve using the abovementioned method and the conventional sterilization process.

Example 1 : Korean Ox Tail Soup One hundred and thirteen pouches with Korean ox tail soup were produced.

Thermistor probes were inserted into five pouches. One pouch was used to determine microbial count using standard techniques. Another pouch was used for taste testing in the factory. Another two pouches were incubated at 39°C and 50°C respectively. A control with a thermistor probe in a water pouch was also used.

Initial temperatures measured by the probe when the retort was started were as follows.

Product consisted of boiled beef tail (including bone) meat (150-158g) and balance of total made up with white bone soup. Tail pieces ranged in weight from 5g to 20g, with a maximum size of 60 x 40 x 20 mm. Filling instructions included that only one (one) large tail peace per bag and balance of solid weight made up on smaller pieces. Therefore probes were inserted into the large tail piece, guaranteeing the SHP (slowest heating point) of the product. Probes were placed at the estimated thermal centres of the pouches, with probed pouches positioned in the retort in areas identified as tending to heat more slowly: • Bottom tray, front of one side • Bottom tray, centre of tray • Middle tray centre of tray • Middle tray right side • Second tray from the top, middle of one side Only one basket contained product, whilst other baskets only contained water bags for thermal holding. The probes used were ET-081 type thermistor probes, with the data recorded via a "Smart Reader Plus 8" logger.

Processing details: Processing temperature: 122 °C (as indicated by the water probe)

Retort temperature setting during "cook" period 122 °C (as indicated by mercury) Hold time at "cook" temperature: 12 minutes Come-Up-time (CUT): 10 minutes

Minimum initial product temperature: 42.41 °C

Calculation Of Fo Of The Process: Fo is the accumulated time of microbial lethality where one unit corresponds to one minute at 121°C. An Fo value equal to or greater than 2.5 is acceptable for meat products. Real time temperature data is attached as Figure 12. The final column in the table shows cumulative Fo value for the slowest heating channel. Fo is calculated by the trapezoidal method. A graph of logged temperatures against time is provided in Figure 10. Probe 4 heated most slowly, so the following calculations are based on this probe.

(i) Calculation by the "General Method" Total Fo = Total accumulated L x time interval = 5.9 min Fo in heating phase = (Total accumulated L during heating phase x time interval) = 4.0 min Fo in cooling phase = Total Fo less F₀ in heating phase = 5.9 - 4.0 = 1.9 min

(ii) Calculation by "Gillespy's Method" The Gillespy method is used to confirm conventional methods and complement where all the data for the general method is not available. The Gillespy calculations are presented in the graph in Figure 11. The associated calculations are shown as follows: f_h = the time to transverse one logarithmic cycle in temperature difference B = processing time L1 = lethality at hold temperature J = lag factor T_ret= Retort temperature

T_A= pseudo initial temperature at .4 x CUT To = initial product temperature at the SHP at .4 x CUT f_h = 11.4 min

j = (92)/(66.66) j = 1.38

CALCULATION OF Fo OF THE PROCESS: (Taking zero time as time when retort turned on)

Retort temperature: 122C Initial prod, temp.: 42.4

Process Time: 12 min Log temp. diff. At 0 time: 1.97

Process time +CUT: 22 min Z= 10C f = 11.4 min Slope = 0.08796748 j = 1.38 Intercept = 1.9666 L1 = 1.230 Cooling period correction 0.08 v = 0.971628 u = 0.459514

Fo = 6.4 min Fo = u x f_h x L U = av² +bv +c where a, b & c are polynomial numbers V = B/f_h - logO(Tret - To)/z] - 0.08 V = 22/11.4 - log[1.38*((122-42.4))/10] - 0.08 V = 0.971628 Therefore u = 0.175 * 0.971628² + .4475 * 0.971628 + -0.1405 = 0.459514

L _{= 10} ^(T-^Tr>² _ ^ Q (122- 121.1)710

= 1.230 Therefore F₀= u x f _h x L 0.459514 x 11.4 x 1.230 6.4 min

Example 2: Korean Beef Cheeks Soup Seventy pouches with Korean Beef Cheeks Soup were produced. Thermistor probes were inserted into five pouches. One pouch was used to determine microbial count using standard techniques. Another pouch was used for taste testing in the factory. Another two pouches were incubated at 39°C and 50°C respectively. A control with a thermistor probe in a water pouch was also used. Initial temperatures measured by the probe when the retort was started were as follows.

Product consisted of boiled cheek meat (150-155g) and balance of total made up with white bone soup. Cheek meat pieces ranged in weight from, 4g to 10g, with a maximum size of 25x15x15mm. Probes were placed at the estimated thermal centres of the pouches, with probed pouches positioned in the retort in areas identified as tending to heat more slowly: • Bottom tray, front of one side • Bottom tray, centre of tray

• Middle tray centre of tray

• Middle tray right side • Second tray from the top, middle of one side Only one basket contained product, whilst other baskets only contained water bags for thermal holding. The probes used were ET-081 type thermistor probes, with the data recorded via a "Smart Reader Plus 8" logger.

Processing details:

Processing temperature: 122 °C (as indicated by the water probe)

Retort temperature setting during "cook" period 122 °C (as indicated by mercury)

Hold time at "cook" temperature: 8 minutes Come-Up-time (CUT): 10 minutes

Minimum initial product temperature: 29.2 °C

Calculation Of F₀ Of The Process Fo is the accumulated time of microbial lethality where one unit corresponds to one minute at 121°C. An F₀ value equal to or greater than 2.5 is acceptable for meat products. Real time temperature data is attached as Figure 15. The final column in the table shows cumulative Fo value for the slowest heating channel. Fo is calculated by the trapezoidal method. A graph of logged temperatures against time is provided in Figure 13. Probe 4 heated most slowly, so the following calculations are based on this probe.

(i) Calculation by the "General Method" Total Fo = Total accumulated L x time interval = 5.5 min Fo in heating phase = (Total accumulated L during heating phase x time interval) = 2.6 min Fo in cooling phase = Total Fo less Fo in heating phase = 5.5 - 2.6 = 2.9 min

(ii) Calculation by "Gillespy's Method" The Gillespy method is used to confirm conventional methods and complement where all the data for the general method is not available. The Gillespy calculations are presented in the graph in Figure 14. The associated calculations are shown as follows: f h = the time to transverse one logarithmic cycle in temperature difference B = processing time L1 = lethality at hold temperature J = lag factor Tret = Retort temperature T_A = pseudo initial temperature at .4 x CUT

To = initial product temperature at the SHP at .4 x CUT

The usual correction for the F₀ added during the cooling period (the 0.08 correction factor) is insufficient for this type of retort process due to the longer cooling period. This correction factor has therefore been adjusted (to 0.386) so the calculated F₀ more accurately, but still conservatively, reflects the measured F₀ for the retort operation.

f_h = 1 /slope of the straight line section of the Slope = 0.092627 f_h = 10.8 Tre_t = Retort temperature TA = pseudo initial temperature at .4 x CUT

To = initial product temperature at the SHP at .4 x CUT j = (Trer T_A) / ( Tret " To) j = (140)/(94) j = 1.489

Retort temperature: 122C Initial prod, temp.: 29.2 C Process Time: 8 min Log temp. diff. At 0 time: 1.97 Process time +CUT: 18 min Z = 10C f = 10.8 min Slope 0.092627 j = 1.489 Intercept = 2.18 L1 = 1.230

Cooling period correction 0.386 v = 0.912873 u = 0.413844

Fo = 5.5 min

Fo = u x f_h x L

U = av² +bv +c where a, b & c are polynomial numbers V = B/f_h - logD(Tret - To)/z] - 0.386 V = 18/10.8 - log[1.489*((122-29.2))/10] - 0.386 V = 0.912873 Therefore u = 0.175 * 0.9128732² + .4475 ^* 0.9128732 + -0.1405 = 0.413844 _ _{1 0} (T-Tr)/z _ Q (122 - 121.1)/10 = 1.230 Therefore u x f _h x L 0.413844 x 11 x 1.230 5.5 min

Example 3: American Meat Balls One hundred and eighty four pouches of American Meat Balls were produced. Thermistor probes were inserted into five pouches. One pouch was used to determine microbial count using standard techniques. Another pouch was used for taste testing in the factory. Another two pouches were incubated at 39°C and 50°C respectively. A control with a thermistor probe in a water pouch was also used. Initial temperatures measured by the probe when the retort was started were as follows.

Product consisted of meatballs with a maximum in size of 45x35x20 mm and weight range from 20g - 26g each. Filling instructions included that twelve meatballs per pack and 20g of BBQ sauce, vacuumed sealed (60%) and then double seal, by secondary sealing machine. The total weight ranged of bagged product was between 300g - 312g. Probes were inserted into the larger meatballs and placed in the thermal centre or SHP (slowest heating point) of the product. Probes were placed at the estimated thermal centres of the pouches, with probed pouches positioned in the retort in areas identified as tending to heat more slowly: • Bottom tray, front of one side • Bottom tray, centre of tray • Middle tray centre of tray • Middle tray right side • Second tray from the top, middle of one side Only one basket contained product, whilst other baskets only contained water bags for thermal holding. The probes used were ET-081 type thermistor probes, with the data recorded via a "Smart Reader Plus 8" logger. Processing details:

Processing temperature: 119 °C (as indicated by the water probe)

Retort temperature setting during "cook" period 1 19 °C (as indicated by mercury)

Hold time at "cook" temperature: 24 minutes

Come-Up-time (CUT): 17 minutes

Minimum initial product temperature: 11.22 °C

Calculation Of F₀ Of The Process Fo is the accumulated time of microbial lethality where one unit corresponds to one minute at 121°C. An F₀ value equal to or greater than 2.5 is acceptable for meat products. Real time temperature data is attached as Figure 18. The final column in the table shows cumulative Fo value for the slowest heating channel. Fo is calculated by the trapezoidal method. A graph of logged temperatures against time is provided in Figure 16. Probe 2 heated most slowly, so the following calculations are based on this probe.

(i) Calculation by the "General Method" Total Fo = Total accumulated L x time interval = 4.9 min Fo in heating phase = (Total accumulated L during heating phase x time interval) = 4.1 min Fo in cooling phase = Total Fo less Fo in heating phase = 4.9 -4.1 = 0.8 min (ii) Calculation by "Gillespy's Method" The Gillespy method is used to confirm conventional methods and complement where all the data for the general method is not available. The Gillespy calculations are presented in the graph in Figure 17. The associated calculations are shown as follows: f_h = the time to transverse one logarithmic cycle in temperature difference B = processing time L1 = lethality at hold temperature J = lag factor T_ret= Retort temperature

T_A= pseudo initial temperature at .4 x CUT

To = initial product temperature at the SHP at .4 x CUT f_h = 1/slope of the straight line section of the Slope = 0.041852 f_h = 23.9 min T_ret = Retort temperature T_A = pseudo initial temperature at .4 x CUT

To = initial product temperature at the SHP at .4 x CUT j = (Trer T_A) / ( Tret - To) j = (92.85)/(72.51) j = 1.28

Retort temperature: 119C Initial prod, temp.: 11.2

CUT Time 17 min

Process Time: 34 min Log temp. diff. At 0 time: 2.03 Process time +.4 x CUT: 41 min log temp diff at .4 CUT 1.86 z = 10C f = 23.9 min Slope = 0.04185257 j = 1.28113 Intercept = 1.968022 L1 = 0.617 Cooling period correction 0.24 v = 0.807443 u = 0.334925

Fo = 4.93 min Fo = u x f_h x L U = av² +bv +c where a, b & c are polynomial numbers V = B/f_h - logO(Tret - To)/z] - 0.08 V = 41/24.6 - log[1.18*((119-11.2))/10] - 0.24 V = 0.791682 Therefore u = 0.175 * 0.807443² + 0.4475 * 0.791682 -0.1405 = 0.334925 L = 1₀ ^(T-^Tr>^/Z _ ^ Q (119 - 121.1)/10 = 0.617 Therefore

Fo u x f _h x L 0.334925 x 23.9 x 0.617 4.93 min Fo = 4.9 min

ADVANTAGES The advantages of the present invention include providing a sterilization method and system where food products are sterilized at relatively lower temperatures thereby minimizing integrity damage to the food product. The present invention concerns a method and system of sterilizing a food product using thermistor probes to accurately monitor the temperature of the food product during sterilisation in a retort and following a predetermined heat curve for the food product type to achieve sterilization in order to maintain maximum product integrity.

VARIATIONS It will of course be realised that while the foregoing has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is herein set forth. Throughout the description and claims this specification the word "comprise" and variations of that word such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps.

Claims

1. A method of sterilizing a food product including positioning the food product in a retort; sterilizing the food product in accordance with predetermined temperatures and pressures over a period of time calculated to produce a substantially sterilized food product; said temperatures are determined with one or more thermistor probes associated with the packaged food product, wherein the predetermined temperature, pressure and time is calculated for each food product type to maintain maximum product integrity.

2. A method of sterilizing a food product as claimed in claim 1 wherein a thermistor probe is positioned through the retort container or package of a sample of the food product for accurately measuring temperatures, said sterilization includes subjecting the food product to heat and pressure over a period of time in accordance with a predetermined heat curve for sterilization of the food product type thereby maintaining maximum product integrity.

3. A method of sterilizing a food product as claimed in claim 2 wherein there is an initial step of determining a heat curve of the predetermined temperatures, pressures and time for sterilization of the food product type and then using the heat curve for sterilization of packages of the food product.

4. A method of sterilizing a food product as claimed in claim 2 or 3 wherein the thermistor probe is operatively connected to a data control means for collection and analysis of the data; said operative connection includes a pressurized flange in the retort wall enabling electrical connection between the thermistor probe and the remotely located data control means.

5. A method of sterilizing a food product as claimed in claim 4 wherein the data control means includes a processor for processing temperature, pressure and time data and operating temperature and pressure control means according to the processed data and the predetermined heat curve.

6. A method of sterilizing a food product as claimed in any one of claims 4 and 5, wherein the thermistor probe has a pointed end to allow the probe to penetrate the food product package.

7. A method of determining a heat curve for the sterilization of a food product for the method claimed in any one of claims 2 to 4 including positioning a thermistor probe through the retort container or package of the food product, sterilizing the food product while measuring the temperature of the food product and pressure within the retort and time elapsed during sterilization; assaying for viable microbial concentration; and determining whether the viable microbial concentration is acceptable for the sale of the food product.

8. A method of determining a heat curve for the sterilization of a food product as claimed in claim 6, wherein the thermistor is inserted into one sample of the food product while a different sample is used for the assay for viable microbial concentration.

9. A system for sterilizing a food product using the method as claimed in any one of claims 4 to 6 including a retort; a thermistor probe insertable within a retortable container or packaged food product; electrical connection between the probe and the data control means, wherein the temperature and pressure is monitored and controlled during the sterilization process.

10. A system for sterilizing a food product using the method as claimed in claim 9, wherein the thermistor probe includes one or more other sensors such as a pressure sensor.

11. A method of producing a food product including preparing the food product; packaging the food product; and sterilizing the food product as claimed in any one of claims 1 to 6.

12. A food product produced by the method claimed in claim 11.

13. A method of sterilizing a food product as claimed in any one of claims 1 to 6, wherein water from the retort is placed in one or more containers depending on the temperature of the water and reused in the retort to shorten the time to reach sterilizing temperatures in the retort, thereby saving time and energy.

14. A method of sterilizing a food product as claimed in claim 13, wherein water is sterilized before it reenters the retort.