Canned packaging containers mainly use tinplate cans, thin-walled glass bottle cans, cooking bags, empty metal cans and empty glass bottle cans, can be purchased directly from designated manufacturers, cooking bags can be purchased prefabricated bags or directly produced by cannery.

 

The empty tank should be inspected before use. It is required that the tank shape is neat, the weld seam is complete and uniform, the tank mouth and the edge of the tank cover are not notched or deformed, and the tin plate is free of rust spots and tin removal. The glass tank shall be of neat shape, smooth mouth, no notch, uniform thickness, and no bubble or crack in the glass. Some empty tanks should be cleaned before they can be installed. After cleaning, they should not be put in place for a long time, so as to prevent re contamination.

 

Canned food production process changes with the variety of varieties and raw materials, but the basic packaging process is generally: filling exhaust sealing sterilization cooling, each process can lead to deterioration of canned food factors, the following will be the main influencing factors analysis:

 

1. Filling process

 

Filling is to load contents into an empty can container. When filling, there should be a certain top gap in the cans, whose size directly affects the food capacity, the vacuum and the deformation of the cans after sterilization. If the top gap is too small and the pressure increases due to food expansion during heating and sterilization, the bottom cover of the cans will protrude outwards, even cracks will occur. If the top gap is too large, the pressure in the cans will be greatly reduced after sterilization and cooling, and the cans will often self-depression. In addition, because of the large top gap, there is more air in the cans, which is easy to cause food. Oxidative discoloration. The size of the top gap should be slightly different according to the type of raw material, the shape of the tank and the state of the raw material. Generally, the top gap should be 6-8 mm when the tank is loaded. Keep the edge of tank mouth clean and dry when filling and filling salt liquid, do not stick raw materials or salt liquid on the tank mouth and affect the sealing.

 

Generally, the filling of cans is made of rotary cup or drum type vibrating tank, both of which are volumetric quantitative. The reasons of unqualified filling quantity are: the capacity of measuring cup is not adjusted correctly, the feeding rate of hopper is too slow or unstable, the charging level of hopper is too low, the feeding tube is too small, the material flow is not smooth, the feeding tube and the measuring cup are not concentric and so on, which will make the measuring cup unsatisfactory. If the container and the feeding pipe are not aligned, the rhythm is not accurate, the container is too small or the material is stuck in the feeding pipe so that the feeding lag will cause material overflow damage.

 

2. Exhaust process

 

Exhaust is to eliminate the air contained in the canned food tissue as far as possible after food filling, so that the pressure in the canned food cans will not be too high due to the expansion of air during heating and sterilization, so that the cans will deform or crack, and at the same time form a certain degree of vacuum in the cans, which can inhibit the residual aerobic microorganisms in the cans. Activity, reduce oxidation corrosion of canned food wall, reduce oxidation loss of nutrients (especially vitamin c), and better preserve the color, aroma and taste of canned food. It is generally required that the central temperature of the exhaust to the sealed tank can reach 70-80 degrees.

 

Vacuum extraction is often used in tinplate tanks-the container and its contents are placed in the sealed volume, the sealed volume is vacuum-pumped, the density of air in the volume is reduced, the vacuum is obtained after sealing, or steam injection method-steam injection is used at a certain temperature and pressure to form a certain vapor condensation after sealing. Vacuum; glass bottles and tanks commonly used thermal exhaust method - before sealing the heater and contents, so that the air density in the bottle is reduced, while hot sealing, cooling after the vacuum or steam injection method; cooking bags using vacuum method, in order to effectively remove the air in the tank, without affecting the quality of the contents, the exhaust should be noted: The varieties with slow heat conduction should be re-boiled before filling, and then discharged with boiling water, and the discharging time should be lengthened properly; the steam condensate should be prevented from dropping into the tank during the discharging process; and the degree of vacuum should be controlled according to the shape, variety and the temperature of soup added. Varieties with soup juice, the vacuum is too high, soup juice is easy to be extracted, too low and often cause the vacuum in the tank is not enough. The general control vacuum degree is 40 to 6. 7 kg.

When heated and exhausted, if the exhaust temperature is too high, it will easily cause the soft rot and breakage of the materials in the tank, and the net weight is insufficient; if the exhaust is insufficient, the vacuum degree in the tank is too low, it will easily cause the cans'sudden cover, the false expansion tank and the corrosion in the tank, and can not effectively inhibit the growth of the aerobic bacteria remaining in the tank, and will affect the inside and outside of the cans during sterilization and cooling. The pressure difference will also indirectly affect the leakage during canned sterilization. The main reason is that the temperature or time of steam or hot water is not up to the requirement.

 

The main reasons of insufficient vacuum degree are: the rate of vacuum pump exhaust decreases; the air passage is seriously leaking or the exhaust pipe is blocked; the instrument of vacuum device fails; the sealing rubber ring inside the glass bottle cap is damaged.

 

3. Sealing process

 

Sealing is to maintain a vacuum in the packaging container, food and the external environment is no longer isolated by external air and microbial contamination caused by corruption, sealing quality does not meet the requirements of food and air contact and oxidative deterioration. The sealing method of tinplate can is a double edge rolling method, in which two rolling rollers with different groove shapes are used to crimp and hook the pre-flanged tank body and the inner circumference of the flanged tank cover.