How canned foods deteriorate during the packaging process

How canned foods deteriorate during the packaging process

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 there is no rust and tin removal on the tinned sheets. The glass jar should be neatly shaped, the jar mouth is smooth and smooth, no gap, 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 avoid 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, exhausting, sealing, sterilization, cooling, and each process has factors that cause canned food to deteriorate. The main influencing factors are analyzed as follows:

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 increases due to the expansion of the food during heat sterilization, which tends to cause the bottom cover of the can to protrude outward, and cracks occur; if the headspace is too large, the pressure inside the can is greatly reduced after sterilization and cooling, often the can The body is sunken itself. In addition, due to the large headspace, there is more air in the tank, which is likely to cause oxidative discoloration of the 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 and affect the seal. ?

The can filling is generally performed by a rotary cup type can or a drum type vibration canning, both of which are volumetric. 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 unsatisfactory, and the feeding tube and the measuring cup are different. Waiting will make the measuring cups unsatisfactory. If the running speed of the machine is too fast, the speed of the material falling from the hopper 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 reflow; if the container is not in contact with the feeding tube, the beat is not allowed. If the container is too small or the material sticks to the material tube, the feed delay will cause the material to overflow. ?

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, a certain degree of vacuum is formed 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 the canned food. The color, fragrance and taste. It is generally required to vent the center temperature in the sealed tank to 70 degrees Celsius to 80 degrees Celsius. ?

The tin can is often vacuumed - the container and contents are placed in a closed volume, the closed volume is evacuated by a vacuum pump, 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 of the steam jet bottle mouth, the steam condensation after sealing forms a certain vacuum. Glass bottle cans are commonly used for thermal exhausting method - heating the container and contents before sealing, so that the air density in the bottle is reduced, heat sealed, and vacuum is obtained after cooling. The retort pouch is vacuumed. In order to effectively remove the air in the tank without affecting the quality of the contents, attention should be paid to the venting: the varieties with slow heat transfer should be reheated before refilling, and hot water can be added, and boiling water is added. Exhaust and extend the exhaust time appropriately. The exhaust process must prevent vapor condensation from dripping into the tank. When using the vacuum pumping method, the degree of vacuuming should be controlled according to the shape of the pot, the variety, and the temperature of the added soup. 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 40-66.7kga. ?

When heating the exhaust gas, if the exhaust gas temperature is too high, it will cause the material in the tank to be soft and rotten, 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 can bone, and cannot Effectively inhibiting the growth of aerobic bacteria remaining in the tank, and affecting the pressure difference inside the tank when the can is sterilized and cooled, and indirectly affecting the leakage when the can is sterilized. The main reason is that the temperature 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 leaked or the pumping pipe is filled; the vacuum device is out of order; the sealing rubber ring inside the glass bottle cap is broken. ?

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 sealing method is a double crimping method in which two pre-flanged can bodies are crimped and hooked to the inner side of the flange-shaped can lid by two wrapping rollers having different groove shapes. The glass jar is mainly screw-sealed - using a jaw, a friction wheel or a friction belt, the metal cap with the claw is rotated relative to the glass bottle with the spiral flange at the mouth and moved axially along the spiral to The top sealant is pressed tightly against the end of the bottle to form a seal. Soft cans are mainly sealed with heat seals. The problems of sealing quality are as follows:

(1) Reasons why the double-side sealing is not strict:

False roll - the curling body hook and the cover hook are not engaged. The problem is the flanging damage caused during the transportation and conveying of the can body. 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 flange 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. ?

Skip--Because the seam is thicker at the weld, the sealing roller is skipped when it passes through the can weld, and the crimp is not pressed. 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. ?

The crimping is not complete - the partial crimping is not fully compressed due to the slipping of the can lid on the indenter or the poor rotation of the sealing roller, etc., which is characterized in that a part of the bead has a normal thickness and a part is super thick. The reason is that the tray pressure is too small, the size or taper of the can lid and the indenter is not suitable, the indenter is worn, the height of the indenter shaft is improperly adjusted, the spacing between the trays is too large, the tray spring is out of order, and the oil is on the indenter or the tray. The indenter is tilted in the axial direction, and the positioning is not allowed. ?

Crimping "teeth" - the hook and the body hook are not overlapped, and the V-shape or protrusion formed at the lower edge of the bead is because the sealing curve of a sealing wheel is not ideal, and the pre-sealing machine or the head sealing roller is adjusted. Too loose, the sealing wheel is worn. If the two sealing rings are adjusted too tightly, the dental defects will be aggravated, the design of the can lid is not ideal, the can lid has wrinkles on the rubberized surface, the inclusions in the curling edge or the sealing rubber in the can lid is too much, and the tray pressure is too high. The actual tank canned capacity is too large, and the sealing wheel bearing is 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 inside of the cap is too tightly sealed, and the inside of the crimping is pinched with debris due to The head sealing wheel was adjusted too tightly, causing the can lid to be too long. The tightness does not meet the requirements. The reason is that the curve of a sealing wheel is unreasonable, the adjustment of the sealing wheel is not suitable, the curve of a sealing wheel is seriously worn, the shape of the rubber surface of the can lid is unreasonable or the surface of the can end is wrinkled, and the sealing wheel bearing does not operate. Flexible and so on. ?

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, which causes the bottle to break. When the speed of the belt is too large, the bottle mouth is broken or the belt speed is too small, so that the bottle cap is not tightly sealed. ?

(3) The reason why the heat-sealed bag mouth is not tightly sealed or the seal is burnt or damaged: the former is mainly because the sealing temperature is too low or the sealing pressure and heat sealing time are not enough; the bag mouth has debris to make the sealing not firm; the heat sealer Bonding the melted plastic; the shaper 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. ?

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. ?

Canned sterilization is often carried out by heat sterilization - heating the product 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 in contact 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 In the case of soup containing food, the high solid content 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, it will prolong the time required for the can to achieve the sterilization effect, making the sterilization formula inappropriate. The high temperature of canned 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 occurs. 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, high salt concentration, and the presence of nitrite and organic acids enhance the thermal effect of sterilization. The high concentration of sugar liquid has a protective effect on bacterial spores. The size of the food block, the high solid content, and the filling method will affect the heat transfer inside the tank. When the sterilization, the degree of microbial contamination in the tank 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 content in the tank is high, and the residual amount is also high, so that the can is not reached. Commercial sterility requirements.

Cooling process?

After the canning is completed, 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 tinplate canned after atmospheric 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 water in the tank, which may cause corrosion of the iron or re-contamination of microorganisms. Due to the poor thermal conductivity of glass bottles, they cannot be directly cooled into cold water after sterilization, otherwise they may cause cracking and should be cooled in stages. ?

After very sterilized cans, the food in the cans expands due to high temperature during sterilization, and the pressure inside the cans increases remarkably. If the normal pressure is quickly restored after sterilization, the internal pressure will be too large and the cans will be deformed or broken, affecting the cans. Sealing performance. Therefore, pressurized cooling is required for such cans, that is, back pressure cooling, so that the pressure in the sterilization pot is slightly larger than the pressure inside the tank, and when the contents of the can are sufficiently cooled, the internal pressure is relaxed, and expansion or cracking does not occur. Pressurization cooling may be performed by steam pressure cooling or by air pressure cooling or by timely cooling the cold water into a sterilization pot. ?

After thermal sterilization, it will still be re-contaminated by microorganisms suspended in canned cooling water or conveyor belts and 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. In the post-cooling stage, when the contents are cooled and the pressure inside the tank drops to form a partial vacuum, there will be a chance of leakage if the water contains enough The amount of microorganisms can also cause re-contamination. ?

The main reason is: structural defects - the deformation and damage of the tank after improperly sealed structure or excessive mechanical handling, destroying the integrity of the can, the cooling water is not clean during the cooling process, and the microorganisms in the capillary of the tank enter the tank Internally caused re-contamination. 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.