Author: Principal Packing Co., Ltd. Guangzhou Fu Zhien
I. The effect of temperature and pressure in the cooking pot on the quality of the high-temperature cooking bag <br High-temperature cooking sterilization is an effective method to extend the shelf life of food, and has been widely used by many food factories for a long time. Commonly used cooking bags have the following structures: PET // AL // PA // RCPP, PET // PA // RCPP, PET // RCPP, PA // RCPP, etc. At present, in Sichuan, Chongqing, Hunan, Zhejiang, and Northeast China, PA // RCPP structure is used more often in the packaging of some cooked meat products. In the past two years, food factories using PA / RCPP have complained more about flexible packaging material manufacturers, and the main problems reflected are delamination and broken bags.
Through investigation, it was found that some food factories had some irregular problems during the cooking process. Generally speaking, the sterilization time should be 30 ~ 40min at the temperature of 121 ℃, but many food processing companies have arbitrary regulations on sterilization time, and some even reach 90min.
When the steam cooker purchased by some flexible packaging companies is 121 ° C, the pressure indication value of some cookers is 0.12 ~ 0.14MPa, and some cookers are 0.16 ~ 0.18MPa. According to a food factory, when the pressure of the cooking pot is 0.2 MPa, the value displayed on the thermometer is only 108 ° C.
In order to reduce the temperature, time and pressure differences that affect the quality of high-temperature cooking products, the temperature, pressure and time relays of the equipment must be calibrated regularly. We know that the country has an annual inspection system for various types of instruments. Among them, pressure instruments are compulsory annual inspection instruments, and the calibration cycle is once every six months. That is to say, under normal circumstances, the pressure gauge should be more accurate. The temperature measuring instrument does not belong to the category of mandatory annual inspection, so the accuracy of the temperature measuring instrument must be compromised.
The correction of the time relay also requires regular internal calibration, which is done by means of a stopwatch or time comparison.
The calibration method of the high-pressure cooking pot used in the experiment and the autoclave used in the food factory is suggested as follows.
Correction method: Inject a certain amount of water into the pot, limit the temperature sensor to be submerged, heat the water to boiling, and check whether the temperature indicator is 100 ° C (in high altitude areas, the temperature at this time may be Between 98 ~ 100 ℃)? Replace the standard meter thermometer for comparison.
Discharge part of the water to expose the temperature sensor to the water surface; cover the pot tightly, increase the temperature to 121 ° C, and observe whether the indication value of the pressure gauge of the cooking pot at this time is 0.107Mpa May be between (0.110 ~ 0.120MPa).
If the above data can be matched during the calibration process, it means that the pressure gauge and temperature gauge of the cooking pot are in good condition. Otherwise, you should ask a professional to adjust the pressure gauge or temperature gauge.
At present, the cooking temperature required by the so-called high-temperature cooking bags produced by most flexible packaging companies is generally 121 ° C, and some companies require 115 ° C or 125 ° C. Few people require a sterilization temperature of 135 ° C. The following two tables are experimental empirical data, which can be used as a process reference for high temperature cooking products.
1) In the case of plastic / plastic composite, it can withstand cooking at 126 ° C for 30 minutes. It is used to process cooking bags with PA / RCPP structure. After delivery, the food factory reports that the bag breaking rate has reached 20%. It is understood that the cooking temperature used by this customer is 121 ° C, and the time is unknown. After collecting the composite samples from customers, sterilize them in the laboratory of our company with 121 ℃ and 126 ℃ for 40min. No bag breaking was observed; however, as the temperature increased, the outward curling phenomenon became obvious. More serious. Before and after cooking at 126 ° C, the shape and geometry of the cooking bag were measured and checked. It was found that the heat shrinkage of the bag reached 6.37%. When the temperature was raised to 135 ° C, some bags were broken.
Inferring from the above phenomenon, the actual sterilization temperature of the food factory must be higher than its claimed 121 ° C. Therefore, as a compound flexible packaging enterprise that produces cooking bags, it should have a full understanding of the requirements of its downstream customers and their actual operation. In this way, when a quality complaint occurs, the real cause of the problem can be quickly found and unnecessary losses avoided. .
2) The packaged food processed by the food factory under the normal cooking conditions of 121 ° C and 20-30 minutes will have a problem of "bag-up" after leaving the factory.
The cause of the "bag expansion" problem is that under the specified cooking conditions, the moisture and gas in the packaging bag are heated to expand, and the gas is a poor conductor of heat. Therefore, under the specified cooking conditions, the center of the packaging content has not reached a thorough level. The temperature and time required for sterilization. Therefore, the remaining microorganisms continue to multiply under appropriate conditions, resulting in "bagging" of sterilized packaging.
In order to achieve the purpose of thorough sterilization, food factories increase the cooking temperature or prolong the sterilization time. The direct result of increasing the cooking temperature is that the air or moisture in the packaging bag expands more severely when heated, and the pressure in the packaging bag is further increased, which significantly increases the breakage rate of the packaging bag.
It is not difficult to see from the above analysis that the reasons for incomplete sterilization and broken bags during cooking are caused by the pressure in the packaging bag being greater than the pressure in the cooking pot. Therefore, how to control the pressure in the cooking pot so that the packaging bag does not swell during the cooking process is the key to solving the problem.
3. Recommended high temperature back pressure cooking pot and basic information
Judging from the working principle and production process, the hot-water spray-type flexible packaging food sterilization device produced by this company is basically consistent with the products of other companies in the world. The following figure is the production process of the experimental equipment.
Reading Table 3 carefully, we can draw the following conclusions:
1. When the pressure gauge reading of the cooking pot reaches 0.1035MPa, the actual pressure (also called absolute pressure) in the cooking pot is 0.2048MPa.
2. When the cooking pot is not filled with any sterilized packaging, and only air is used, the cooking pot is closed and vented with high-pressure steam. When the pressure gauge of the cooking pot shows 0.1035 MPa, the The temperature is only 92.7 ° C.
3. If the shelf and the sterilized packaging in the cooking pot occupy 50% of the space in the pot, and the other half is air, close the cooking pot and put in high pressure steam. When the pressure gauge of the cooking pot shows 0.1035 At MPa, the temperature in the cooking pot was only 109.2 ° C.
4. If the shelf in the cooking pot and the sterilized packaging occupy 50% of the space in the pot, and the other half is air, close the cooking pot and pass in high-pressure steam. While heating, open the exhaust valve After slowly and 100% exhausting the air in the cooking pot, when the pressure gauge of the cooking pot shows 0.1035 MPa, the temperature in the cooking pot can reach 121 ° C.
Different from other enterprises: this enterprise will also provide the AMMU control system (Advanced Monitoring Management Unit). This system integrates HISAKA WORKS LTD's many years of experience in applying cooking and sterilizing devices, which can effectively solve the problem of broken bags in cooking bags during sterilization.
Customers who use high-temperature cooking pots know that during the high-temperature sterilization process, "back pressure" needs to be applied to the pot to prevent the cooking bag from breaking. It is rarely reported when "back pressure" is applied and how much "back pressure" is appropriate.
HISAKA WORKS LTD controls the temperature and pressure of the cooking pot as two independent parameters. They calculated the vacuum bags, water-containing packaging bags, and gas-containing packaging bags containing different types of contents based on heat transfer theory, and calculated that when the required temperature was reached, the gas in the packaging bag was expanded by heat and the water was evaporated after heating. The pressure value formed inside applies a "back pressure" of the same value to the cooking pot, so that the pressure inside and outside the bag is balanced, thereby completely eliminating the possibility that the cooking bag is deformed, wrinkled and broken.
Fourth, the solution of high-temperature cooking products after cooking, "bubbles" appear locally in the product <br /> If bubbles appear, enterprises should focus on controlling the following aspects during production:
1) Whether the temperature resistance of the ink meets the requirements of high temperature cooking and sterilization conditions; (The choice of white ink and curing agent is very important. The soft pack factory needs multiple experimental verifications before it can be put into normal production and use.)
2) The natural curing time of printing materials needs to reach more than 24h to ensure the sufficient curing of ink and the volatilization of residual solvents;
3) The choice of compound high-temperature glue is very important; (The amount of curing agent is increased by 10% based on the manufacturer's standard ratio. To calculate the consumption of curing agent when the humidity in the workshop is high, the moisture in the air.)
4) To ensure the uniformity of the sizing of the composite roll, and to ensure that the dry-based coating amount is 3.8 ~ 4.2g / m2;
5) The supply and exhaust air volume of the composite oven needs to be guaranteed;
6) The temperature of the compound roller is 65 ~ 70 ℃, the temperature of the three-stage oven is 70 ℃, 80 ℃, 90 ℃, and the machine speed is 90 ~ 100 m / min;
After the above 5) and 6) two indicators are completed, the solvent residue when the compound finished product is lowered to the machine can be less than 5.0 g / m2;
7) The control of the compounding process also needs attention.For example: the high temperature cooking structure is PET12 // AL9 // PA15 // RCPP70, then the compound is first produced AL9 // PA15, and then matured for 48 hours; after the curing is completed, the printing material is compounded and then compounded RCPP layer, the final maturation of 96 hours or more before cooling and slitting. Ripening conditions: 50 ~ 55 ℃, the time is more than 96h, and it can be ripened for 120h under conditions.
8) For printing (SIO2) PET12 materials, pay special attention to the choice of the material supplier; (The quality stability of coating and evaporation is very important.)
9) AL uses high-temperature cooking grade, (pinholes are controlled within 100 / m2, the oil removal level reaches A grade, and the tensile strength and elongation must be strengthened