​retort process calculation

retort  process calculation

one. What is the sterilization process?

Each retort machine must be subjected to the following process of sterilization, heat-incubation and sterilization – counter-pressure cooling and cooling. The sterilization process is to control the control parameters used in the retort machine, also called the sterilization procedure and the sterilization curve. The sterilization process includes three factors, temperature, time and back pressure. It is usually expressed in the form of “sterilization formula” in the food factory, that is, the sterilization temperature, time and the counter pressure used are arranged in the form of a formula. The general sterilization formula is: t1-t2-t3 or (t1-t2), P goes through three stages: first, after the temperature rise phase, the time is τ1, the predetermined sterilization temperature t is reached; after the thermostatic sterilization phase, the time is τ2; During the cooling and cooling phase, the time is τ3; for high-temperature sterilization cans, some need to pass compressed air back pressure to cool P. The above parameters time, temperature and back pressure are the process conditions for sterilization.

two. Three calculation methods common to sterilization process

Improved Basic Law:

 In 1920, Bigelow first established the theory of food sterilization, and proposed the general mathod, which is also called the basic algorithm. The method proposes the concept of partial sterilization rate, which calculates the lethal effect of the whole heat sterilization process by calculating the lethal rate at different temperature-time combinations in the whole heat sterilization process including the heating and cooling stages. In 1923, Ball developed an improved general method based on the method of calculating the bactericidal effect by the integral of the heating effect of the food center during the heat sterilization process. This method improves the accuracy of calculations and becomes a widely used method. During the sterilization process, the temperature of the food will change continuously with the change of the sterilization time. When the temperature exceeds the lethal temperature of the microorganism, the microorganism will die. The rate of microbial death varies with temperature. There is a certain bactericidal effect when staying at the lethal temperature for a while. The whole sterilization process can be regarded as the sum of the sterilization effects obtained by staying at different sterilization temperatures for a certain period of time.

 Formula calculation method:

 This method was proposed by Bauer and later simplified by the Thermal Engineering Research Group of the American Can Company to calculate the sterilization time and F value on the simple and transitional heat transfer curves. Simplification introduces some errors but has little effect. This method has been included in the relevant regulations of the US FDA and is widely used in the United States. The formula method is based on the heating curve drawn on the semi-logarithmic paper by the change of the temperature of the contents of the can in the sterilization process, and the curve of the cooling water immediately entering the retort machine after sterilization to calculate and find out the answer. The advantage is that the sterilization time can be calculated when the sterilization temperature is changed. The disadvantage is that the calculation is cumbersome, time-consuming, and it is easy to make errors in the calculation, and the heating curve must have a regular simple heating curve or a turning heating curve. Get a more accurate result.

In recent decades, many scholars have studied this method in order to achieve the purpose of being correct, simple, and convenient to apply. With the application of computer technology, the formula method is as accurate as the improved method, but it is faster and more concise. Line chart method:

The nomogram method is to calculate the relevant parameters into a column line calculation map, and use the map to calculate the sterilization value and the sterilization time. The method is applicable to any simple heating curve of Z=10°C and m+g=76.66°C, which is quick and convenient, but cannot be used for the calculation of the turning type heating curve. When the data is out of line, it cannot be calculated by this method.

three. Representation method of sterilization curve

Usually arranged in the form of a formula, it is also called a sterilization formula, also called a sterilization procedure. Τ1—τ2—τ3 P t is not the relationship of addition, subtraction, multiplication and division. Τ1 heating time min, τ2 constant temperature sterilization time min, τ3 cooling time min, t sterilization (pot) temperature °C, attention does not refer to the center temperature of the can. The back pressure at P cooling is 0.12 – 0.13 MPa. Τ1 is generally about 10 minutes, and τ3 is generally 10 minutes to 20 minutes. Faster is better, that is, rapid temperature rise and rapid temperature drop are beneficial to the color and flavor of the food and the nutritional value. However, it is sometimes limited by conditions, such as insufficient steam pressure in the boiler and prolonged heating time; when the can is easy to be fat, damaged, etc. during cooling, it is not allowed to be too fast. The main task at present is to determine τ2, t, the most trouble is to determine τ2, requiring the sterilization formula to minimize the sterilization time under the premise of preventing corruption. It can prevent corruption and protect quality as much as possible.


Sterilization formula – Table 1

  The following is the existing mature sterilization formula: 

Luncheon meat: 10 min – 60 min – 10 min / 121 ° C, back pressure 0.12 MPa. 

Canned mushrooms: 10 min – 30 min – 10 min / 121 ° C 

Orange canned: 5 min – 15 min – 5 min / 100 ° C

four. Determination of sterilization conditions

First understand a few concepts.

 1. Actual sterilization F value: refers to the total sterilization effect under a certain sterilization condition. Actual sterilization F value: The sterilization time at different temperatures is converted into a sterilization time of 121 ° C, which is equivalent to the sterilization time of 121 ° C, expressed by F real. Special Note: It does not refer to the time spent by the actual operation of the worker. It is a theoretically converted time. To help you understand and remember, please see the examples I designed for you. Example: a canned food is sterilized at 110 ° C for 10 min, sterilized at 115 ° C for 20 min, and sterilized at 121 ° C for 30 min. The actual sterilization operation time of the worker is equal to 50 min, and the actual sterilization F value is not equal to 50 min. F real = 10 × L1 + 15 × L2 + 30 × L3, L I call it the conversion factor. L1 is definitely less than L2, both of which are less than one. Excuse me, L3=? F is definitely less than 50 min, so it can be seen that the actual sterilization F value is not the sum of the total time of the sterilization process of the factory. Example: sterilization at 100 ° C for 90 minutes, sterilization at 120 ° C for 10 minutes, which sterilization strength is large? Converted to the sterilization time equivalent to 121 ° C, and then compare! 90×L100 and 10×L120 comparison! Just find the conversion factor and compare it.


2. Safe sterilization F value The heating time required to kill a certain amount of microorganisms or spores at a constant temperature (121 ° C). It is used as a standard value for judging the rationality of a certain sterilization condition, also called the standard F value, expressed by F An. "Killing" has the meaning of commercial sterilization, allowing the presence of live bacteria. F An indicates the sterilization time (121 ° C) required to meet the canning rate requirements, and the standard sterilization time required for each can (usually 121 ° C is the standard temperature), just like other food standards, used as a reference to determine whether it is qualified. Whether it meets the requirements. It is also the main basis for determining the constant temperature time τ2 in the sterilization formula. For example: a can F A = 30 min, indicating that the can is required to sterilize at 121 ° C for 30 min. F application examples of F and F An application examples: F is equal to or slightly larger than F safety, and the sterilization is reasonable. F is less than F safety, insufficient sterilization, does not meet the standard, and must be corrupt. The sterilization time must be extended. F is far greater than F An, excessive sterilization, super standard sterilization, affecting color and flavor, nutritional value. It is required to shorten the sterilization time. Due to this comparison and repeated adjustments, a suitable τ2 can be found.

 3. Calculation of safe sterilization F value

 A determines the sterilization temperature t:

Cans PH is greater than 4.6, generally 121 ° C sterilization, very few less than 115 ° C sterilization. Cans PH is less than 4.6, generally 100 ° C sterilization, very few less than 85 ° C sterilization. In practice, PH meter detection can be used, and it can be roughly estimated based on life experience. For example: B first select the target bacteria: the spoiled microbiology leader, the key target of sterilization. It has strong heat resistance and is not easy to kill. It can often occur in cans and is the most harmful. As long as it is killed, other spoilage bacteria, pathogens and enzymes will definitely kill. According to the basic experiments of microorganisms: F An = D (lga-lgb) The following is explained at a standard temperature of 121 ° C, because the sterilization of high temperature is more complicated and people pay more attention to it. F Ang generally refers to the standard sterilization time at t temperature (121 ° C) and the required sterilization time. D generally refers to the sterilization time required to kill 90% of microorganisms at t temperature (121 ° C). It is a characteristic parameter of microbial heat resistance, and the larger the D value, the stronger the heat resistance. D values are obtained from microbiological experiments. Common D values can be found in the relevant manual.


To help you understand and remember,

Example: It is known that the mushroom canned bacteria D121 = 4 min, want to kill 99.9% of the target bacteria at 121 ° C, ask how long sterilization time? If the number of viable bacteria is reduced to 0.01%, how long does it take to sterilize?

  The first D value, killing 90%,

The second D value kills 9%,

  The third D value, killing 0.9%,

The fourth D value kills 0.09%.

  Answer: 12 min,

16 min a number of original viable cells per unit volume / number of bacteria per can. b Residual viable bacteria / canned spoilage rate.

   Example: Canned Mushrooms –

  F An = D (lga-lgb) = 4 (lg850-lg5 × 10-4) = 24.92 min, thus obtaining a standard time for mushroom cans to be sterilized at 121 ° C – 24.92 min.

  Solved the problem of the sterilization standard of mushroom canned F.


4, the actual sterilization F value calculation F real =?

 (1) Summation method F is calculated according to the center temperature of the can, and the sterilization time at different temperatures is converted into a sterilization time of 121 ° C, and then added up.

 F real = t1 × L1 + t2 × L2 + t3 × L3 + t4 × L4 + …… L lethal rate value, the actual sterilization time at a certain temperature is converted to a conversion factor of 121 ° C sterilization time, below we solve the L lethality, The problem of the conversion factor.

 Calculated by the formula L=10t-121/Z. t is the central temperature of a certain period of time in the can sterilization process, and Z is another heat resistance characteristic parameter of the target bacteria. What is another? The temperature change required to change the thermal lethal time by a factor of 10 is the Z value. F indicates the death time of heat, and if it is not F, F, it means the time of death. Please see the example: target bacteria Z = 10 ° C, F121 = 10 min, find F131 = ? Min, F141 = ? Min, F111 =? Min, F101= ? Min. The temperature change required to change the thermal lethal time by a factor of 10 is the Z value.

 In turn, it is understood that the temperature change of 1 Z value thermal lethal time change will change 10 times. Please see the example: Subject Z = 10 ° C, F121 = 10 min, F131 = 1 min, F141 = 0.1 min, F111 = 100 min, F101 = 1000 min. Solve the problem of L fatality rate and conversion coefficient. Just example: A can of 10 ° sterilized at 110 ° C, sterilized at 115 ° C for 20 min, and sterilized at 121 ° C for 30 min. The actual sterilization operation time of the worker is equal to 60 min, and the actual sterilization F value is not equal to 50 min. F real = 10 × L1 + 20 × L2 + 30 × L3 = 10 × 0.079 + 20 × 0.251 + 30 × 1 = 38.32min

It can be seen that the actual sterilization F value is not the sum of the total time of the sterilization process of the factory. Example: sterilization at 100 ° C for 90 minutes, sterilization at 120 ° C for 10 minutes, which sterilization strength is large? Converted to the sterilization time equivalent to 121 ° C, and then compare! 90×L100 and 10×L120 comparison, 90×L100=90×0.008=0.72 min 10×L120=10×0.794=7.94 min It can be seen that the high temperature sterilization canned food has no effect at 100°C sterilization, and must be produced. note. Explain the example of canned sterilized quail eggs in jooyan sterilizing pot.


Sterilization formula


Sterilization formula – Table 3

Sterilization formula 1:

F is equal to or slightly larger than F, and sterilization is reasonable. The temperature sterilization time is only 23 min, but the whole sterilization process is equivalent to the actual sterilization time of 25.5 min at 121 °C, and the other 2.5 min is obtained by heating and cooling. The actual sterilization process time of the factory is nearly 50 minutes, and the time for the cans to enter the pan is at least one hour. Sterilization formula 2: F is more than F-an, over-sterilization, super-standard sterilization, affecting color and flavor. It is required to shorten the sterilization time. In this way, the thermostat sterilization time is adjusted, thereby finding τ2.

 At present, some factories use computer-controlled sterilization. The central temperature record and the F-real calculation are all done by computer. When F is equal to or slightly larger than F-an, the sterilization process is automatically stopped, and we do not need to calculate it. Determination of the process conditions for canned sterilization: τ1—τ2—τ3 P t Back pressure of the sterilization kettle: Generally, A glass bottles, B large tanks, and C soft cans require back pressure sterilization or back pressure cooling, and compressed air is used to maintain the pressure gauge during cooling. The reading is 0.12—0.13Mpa. The above contents are all methods for theoretically determining the process conditions for can sterilization.

Fives. How to design and calculate new product sterilization process

After installing the retort machine in the enterprise, jooyan mechanical engineers will help you test and input the sterilization process. However, as the enterprise develops, when it is necessary to develop new products, how to quickly design the sterilization process? If you want to develop canned stewed snake meat, please formulate the sterilization process conditions? According to the above content: through the microbiological detection, find the target bacteria, find F An, and then compare with F and constantly adjust, and finally get a reasonable sterilization formula.

A lot of canned sterilizing conditions have been available, and the canned sterilizing conditions are used as reference for information. For new varieties, you can make a bold estimate.

The estimated empirical principles are as follows:

 A acid-containing food: 85-100 ° C, 10-30 min, acidic beverages used 85 ° C, 15 min,

 B plant / vegetable canned: 115-121 ° C, 15-30 min, protein beverages used 121 ° C, 15 min,

C animal canned food: 115-121 ° C, 50-90 min,

Description: 1 upper limit of the upper tank, the upper limit of the hard cook, the upper limit of the solid, the upper limit of the acidity. 2121 ° C, 100 ° C is two standard sterilization temperatures, commonly used. According to the above experience principle, the sterilization conditions of canned stewed snake meat can be formulated as follows: Most of the canned stewed snake meat can be packed in small cans, which can be used for back pressure sterilization.

 Τ1—τ2—τ3 P t ↓

Sterilization formula 1 10 min – 50 min – 10 min 118 ° C

Sterilization formula 2 10 min—55 min—10 min 116°C

In practice, do some sterilization and heat preservation experiments to fine-tune the constant temperature time. After the sterilization process is completed, fine adjustment is also carried out in practice, mainly according to the shelf life and the taste. If the shelf life is short, the sterilization temperature or sterilization time can be increased. If the hardness of the product is very poor, it will be soft and rot, which can reduce the sterilization temperature or time. For example, after sterilization, the product has a phenomenon of rising the bag and increasing the back pressure. With the development of automatic retort machines, Zhucheng Zhongyuan Machinery Co., Ltd. has developed more intelligent sterilization equipment, which can better guarantee the sterilization process requirements, make the products taste better, taste better and consume less energy.