Canned packaging containers mainly use tinplate cans, thin-walled glass jars, retort pouches, empty metal cans and empty glass jars, which can be purchased directly from designated manufacturers. The retort pouches can be purchased from prefabricated bags or directly from canning production plants.
Empty cans should be inspected before use. It is required that the cans are neat, the welds are completely uniform, the edges of the cans and can ends are not chipped or deformed, and the tin plate is free of rust and tin. The glass jar should be neatly shaped, smooth and smooth, without gaps, uniform thickness, no bubbles and cracks in the glass. Some empty cans should be cleaned before being filled, and it should not be left for a long time after cleaning to prevent re-contamination.
The production process of canned foods varies with the variety of materials and raw materials, but the basic packaging process is generally: filling → exhaust → sealing → sterilization → cooling, each process has factors that cause canned food deterioration, below The main influencing factors are analyzed as follows:
1. Filling process
Filling is the loading of the contents into an empty can container. When filling, there must be a certain head gap in the can, the size of which directly affects the capacity of the food in the tank, the degree of vacuum and the deformation of the can after sterilization. If the headspace is too small, the pressure will increase due to food expansion during heat sterilization, which will cause the bottom cover of the can to protrude outwards and even cracks. If the headspace is too large, the pressure inside the can is greatly reduced after sterilization and cooling, often the can body Self-recession, in addition, due to the large headspace, there is more air in the tank, which is easy to cause oxidative discoloration of food. The size of the headspace is slightly different depending on the type of raw material, the shape of the tank, and the state of the raw material. Generally, the top gap is 6-8 mm when the can is filled. Keep the edge of the tank clean and dry when filling and salting. Do not stick the raw material or salt to the tank to affect the seal.
The can filling is generally performed by a rotary cup type Measuring Cup or a drum type vibration canning, both of which are volumetric quantitative. The reason for the unsatisfactory filling amount is that the capacity of the measuring cup is not adjusted correctly, the feeding of the hopper is too slow or unstable, the loading surface of the hopper is too low, the feeding tube is too small, the material flow is not good, and the feeding tube and the measuring cup are different. If the machine is running too fast, the speed of the hopper falling material will be too fast, which will cause the material to be recirculated and the filling amount will be too much. If the measuring cup expansion mechanism is improperly adjusted, it will cause excessive recirculation; if the container and the feed are If the tube is not in the same heart, the beat is not accurate, the container is too small, or the material sticks in the material tube, the feed delay will cause the material to overflow.
2. Exhaust process
Exhaust is to remove the air contained in the canned food tissue as much as possible after the food is filled, so that the canned body does not cause excessive pressure in the tank due to thermal expansion of the air during heat sterilization, so that the can body is deformed or the can seam is loose. At the same time, it also forms a certain degree of vacuum in the tank, which can inhibit the activity of aerobic microorganisms remaining in the tank, reduce the oxidative corrosion of the tank wall and reduce the oxidation loss of nutrients (especially vitamin C), and better preserve canned food. Color, fragrance, taste. It is generally required to vent to a center temperature of 70-80 degrees in the sealed tank.
Tinplate cans are usually vacuumed - the container and contents are placed in a closed volume, the vacuum volume is used to evacuate the closed volume, the air density in the volume is reduced, the vacuum is obtained after sealing, or the steam injection method - with a certain temperature The pressure steam jet bottle mouth, after the sealing, the steam condenses to form a certain vacuum; the glass bottle tank is commonly used for the thermal exhaust method - the container and the contents are heated before sealing, so that the air density in the bottle is reduced, the heat is sealed, and the cooling is obtained. Vacuum or steam injection method; the retort pouch is vacuumed. In order to effectively remove the air in the tank without affecting the quality of the contents, the exhaust should be noted: the type with slow heat transfer should be taken after re-cooking before canning. Packing, adding boiling water and then venting, and appropriately lengthening the exhaust time; the exhaust process must prevent steam condensation from dripping into the tank; when vacuum pumping is used, it should be controlled according to the shape of the tank, the variety, and the temperature of the soup. The degree of vacuum. The variety with the soup, the degree of vacuum is too high, the soup is easy to be extracted, too low and often cause insufficient vacuum in the tank. Generally, it is preferred to control the degree of vacuum 40-66.7kpa.
When the exhaust gas is heated, if the exhaust gas temperature is too high, it will easily cause the soft and ruptured material in the tank to be broken and the net weight is insufficient; if the exhaust gas is insufficient, the vacuum in the tank is too low, which may cause corrosion of the canned cover, the false expansion tank and the tank. It can not effectively inhibit the growth of aerobic bacteria remaining in the tank, and will affect the pressure difference between the inside and outside of the tank during sterilization and can also indirectly affect the leakage of the can. The main reason is that the temperature or time of the steam or hot water used does not meet the requirements.
When vacuuming and exhausting, the main cause of insufficient vacuum is: the pumping rate of the vacuum pump is reduced; the gas path is seriously leaking or the pumping pipe is blocked; the vacuum device is out of order; the sealing rubber ring inside the glass bottle cap is broken.
3. Sealing process
The sealing is to maintain the vacuum in the packaging container. The food is isolated from the external environment and is no longer caused by the pollution of the outside air and microorganisms. The quality of the sealing does not meet the requirements, and the food will be in contact with the air and oxidized and deteriorated. The tinplate can sealing method is a double crimping method - using two winding rollers with different groove shapes, the pre-flanged can body and the inner periphery of the flange-shaped can lid are curled and hooked together; the glass jar is mainly used Screw-on seal - use the jaws, friction wheel or friction belt to rotate the metal cap with the claws and the glass bottle with the spiral flange at the mouth and move it along the spiral axis to make the top of the cover The sealant is pressed tightly at the end of the bottle to form a seal; the soft can is mainly sealed by heat sealing. The problems of sealing quality are as follows:
(1) Reasons why the double-side sealing is not strict:
False roll - the hook of the curling body and the hook of the cover are not engaged, because the flanging damage caused during the transportation and conveying of the can body is unsatisfactory, the shape of the can body is not qualified, the rounded edge of the can is defective or damaged, and the can is sealed. The cover is not aligned with the can body, etc.
Large sag - when the can is sealed, the edge of the can body or the lid of the can is severely touched, so that the can body and the can lid are not hooked together, and the can body is exposed at the lower part of the hem, because the can body is transported. The flanging damage caused during the conveying process is unsatisfactory in the shape of the flanging of the can body, the rounded edge of the can lid is damaged or the rounded edge is too large, and the can lid is not aligned with the can body when sealing.
Jumping - Because the seam is thicker at the weld, the sealing roller is skipped when it passes through the can weld and cannot be crimped. The reason is that the sealing machine runs too fast and the two sealing wheel buffer springs are too soft. The seam of the can body is too thick.
Incomplete crimping - partial crimping due to slippage of the can lid on the indenter or poor rotation of the sealing roller is characterized by a normal thickness of a portion of the bead and an extra thick portion. The tray pressure is too small, the size and taper of the can lid and the indenter are not suitable, the indenter is worn, the height of the indenter shaft is improperly adjusted, the spacing between the tray and the tray is too large, the tray spring is out of order, and the oil is pressed on the indenter or the tray. The head axis is tilted, the positioning is not allowed, and so on.
Crimping "teeth" - the hook and the body hook are not overlapped, and the v-shape or protrusion on the lower edge of the bead is caused by the unsatisfactory sealing curve of a sealing wheel, the pre-sealing machine or the head sealing roller Too loose, the sealing wheel is worn, and the two sealing wheels are too tight to aggravate the tooth defects. The design of the can lid is not ideal. The can lid has wrinkles on the rubberized surface, and the inside of the crimping is pinched or sealed inside the can lid. Too much glue, too much tray pressure, too much canned cans, and the sealing wheel bearings are not flexible.
Crimping of the curling edge - the outer layer of the iron sheet is broken at the seam of the can body. The reason is that the two sealing rings are adjusted too tightly, the material of the can lid is defective, the sealing glue inside the cover is too much, and the debris is caught in the curling edge. Because the head sealing wheel is adjusted too tightly, causing the can lid to be too long, etc.; the tightness does not meet the requirements, because the sealing curve of the sealing wheel is unreasonable, the sealing wheel is not properly adjusted, and the curve of one sealing wheel is seriously worn. The shape of the rubber surface is unreasonable or the rubber surface of the can lid is wrinkled, and the sealing wheel bearing is not flexible.
Crimping damage - damage to the outer surface of the crimped part or peeling of the coating, because the curve of a sealing wheel is unreasonable, the smoothness of the curved surface of one or two sealing rings is low or the wheel is tightly adjusted.
(2) The reason why the sealing of the glass bottle is not strict: the gap between the bottle turning plate and the bottle holder is not uniform or the movement of the whole machine is uncoordinated, causing the bottle to break; the speed of the belt is too large, so that the bottle mouth is broken or too small. Make the cap tightly sealed.
(3) The sealing of the heat-sealed bag mouth is not strong or there is burnt or broken at the seal : the former is mainly because the sealing temperature is too low or the sealing pressure or heat sealing time is not enough; the bag mouth has debris to make the sealing not firm; heat sealing The glue is bonded to the melted plastic; the former is not centered with the material during bag making, so that the seam edges of the bag are not aligned; the latter is mainly caused by excessive heat sealing time or excessive temperature or excessive pressure.
4, sterilization process
The purpose of sterilization of canned food is to kill microorganisms that cause damage to food and produce poison. When sterilizing, try to preserve the original color, flavor, texture and nutritional value of the food. If the sterilization is not complete, the microorganisms in the cans will multiply when the conditions are suitable for growth, and the food will be spoiled.
The sterilization of canned food is usually carried out by heat sterilization method. The product is heated to a certain temperature for a certain period of time to kill the bacteria. The heat source is mostly steam or hot water, and each can can be directly contacted with the heat source during sterilization. There are many factors affecting the bactericidal effect, mainly the following: improper canning sterilization formula (temperature or time can not meet the requirements); steam sterilization and exhaustion is not sufficient or hot water sterilization convection is not good, etc., causing cold spots in the sterilization pot Including soup food, if the solid content is too high, it will affect the convective heat transfer effect in the tank or the filling in the tank will be too full to affect the stirring function of the headspace gas; if the initial temperature is too low, the time required for the canning to reach the sterilization effect will be prolonged. The sterilization formula is not suitable; the high temperature of the can sterilization will temporarily soften the rubber cap of the bottom cover. When the can is cooled to form a vacuum after the sterilization is completed, it is possible to suck in a small amount of cooling water, especially when the quality of the curling is not good. Micro-leakage; the nature and chemical composition of foods are the environmental conditions in which microorganisms are present during sterilization. The acid, sugar, protein, oil, and salt of foods can affect the heat resistance of microorganisms; other factors such as low pH of food, salt High concentration, the presence of nitrite and organic acid can enhance the thermal effect of sterilization, while the high concentration of sugar liquid has a protective effect on bacterial spores, food block size, The content of the shape and the shape of the can affect the heat transfer in the tank; the degree of microbial contamination in the tank during sterilization is high, and the amount of microbial residues in the tank after sterilization is proportional to the initial number of bacteria. After the same sterilization condition, the bacteria in the tank If the content is high, the residual number is also high, which will make the cans not meet the commercial sterility requirements.
5. Cooling process
After the canning has been sterilized, it must be cooled rapidly. Otherwise, the food in the can still maintains a relatively high temperature and continues to cook, which will change the color and flavor of the product, and sometimes the structure will be affected. The canned tinplate after normal pressure sterilization is directly put into cold water, and is taken out when the tank temperature is cooled to about 40 ° C. The residual heat in the tank is used to evaporate the water attached to the outside of the tank. If the cooling is excessive, the moisture attached to the tank is not easily evaporated. In particular, it is difficult to evaporate the water in the tank, which may cause corrosion of the iron or re-contamination of the microorganisms; the glass bottle can not be directly cooled into the cold water after sterilization due to poor thermal conductivity, otherwise it may cause cracking and should be cooled in stages.
After the very sterilized can, the food in the can is expanded due to the high temperature during sterilization, and the pressure inside the can is significantly increased. If the normal pressure is quickly restored after the sterilization is completed, the internal pressure is too large and the can is deformed or broken, affecting the can. Sealing performance, therefore, such cans should be pressurized cooling, that is, back pressure cooling, so that the pressure in the sterilization pot is slightly larger than the pressure inside the tank, until the contents of the can are sufficiently cooled, and the internal pressure is relaxed, no expansion or cracking occurs. The pressurized cooling may be performed by steam pressure cooling or by air pressure cooling or by blowing cold water into a sterilization pot for cooling.
After heat sterilization, it is re-contaminated by microorganisms suspended in canned cooling water or on conveyor belts or on unclean surfaces of handling equipment. Water is the main carrier for microorganisms to pass through the leakage channel of the packaging container seal or damaged structure. When the content is cooled and the pressure inside the tank drops to form a partial vacuum in the later stage of cooling, there is a chance of leakage if the water contains a sufficient amount. Microorganisms can cause re-contamination.
The main reason is: structural defects - the tank is deformed or damaged by improper sealing structure or excessive mechanical handling, which destroys the integrity of the can. During the cooling process, the microorganisms in the capillary of the tank enter the tank and cause recontamination. The cooling water is not clean. The main cause of can damage is impact or pressure. When the speed of the can on the conveyor belt is slowed down or the direction of conveyance is changed, the impact on the can occurs when it collides with other cans or other parts on the conveyor belt; When transported on the conveyor, its forward movement is blocked and the conveyor belt is still moving, and the can is crushed and damaged.
In order to ensure the quality of food canned food and protect the health of the people, it is necessary to follow the rules in the packaging process and in the process of storage and transportation to avoid the corruption of canned food during storage.
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