What causes vacuum packaging bags to inflate during storage?

Several clients recently reported that, during their packaging upgrades, the number of air pockets in their vacuum-packed bags increased significantly after two weeks, resulting in a noticeable decrease in vacuum pressure and severely impacting product quality. What can be done? Today, Shunxingyuan Packaging, a professional flexible packaging manufacturer, will analyze the causes and solutions for bag swelling during storage based on its own experience.

1. Causes

If bag swelling is a widespread phenomenon, the possible causes are as follows:

1. Insufficient barrier properties of the packaging bag;

2. Gas-producing bacteria are at work after vacuum packaging.

3. Incomplete sterilization.

We can determine whether the poor barrier properties of the packaging bag itself is the main cause through a simple comparative experiment! For example, if rice is packaged, and the vacuum remains good after a period of time (two weeks), it indicates that the barrier properties of the packaging material are not the main factor causing bag swelling.

Experiments have shown that when the oxygen concentration in the packaging bag is ≤1%, the growth and reproduction rate of microorganisms decreases sharply; when the oxygen concentration is ≤0.5%, most microorganisms will be inhibited and stop reproducing. (Note: Vacuum packaging cannot inhibit the reproduction of anaerobic bacteria and the spoilage and discoloration of food caused by enzymatic reactions. Therefore, it must be combined with other auxiliary methods, such as refrigeration, freezing, dehydration, high-temperature sterilization, irradiation sterilization, microwave sterilization, and salt pickling, to achieve a sterile effect).

Incomplete sterilization often leads to microbial exceeding standards. The reasons mainly lie in two aspects: firstly, unreasonable sterilization processes, with deviations in sterilization temperature and time; secondly, improper or erroneous operations leading to unstable quality.

Reasons for sterilization deviations in food:

1. Deviations caused by equipment and instruments: The sterilizer is not installed according to technical requirements, resulting in uneven heat distribution; water, steam, or air leaks in the pipeline system; leaks in the pot door or body; incomplete insulation layer of the pot body, leading to uneven temperature; steam, compressed air, and tap water below the standard; damaged or inaccurate mercury thermometers; malfunctioning automatic temperature recorders or misalignment of the pointer arc with the recording paper, or temperature fluctuation range exceeding that of the mercury thermometer;

2. Deviations caused by product formation: Sterilization initial temperature below process requirements; maximum filling volume exceeding regulations; product PH value exceeding the specified range; changes in production lines or formulas; changes in loading methods, causing overlapping arrangement of cans or improper use of pads exceeding the maximum water activity;

3. Operational errors: The time from can sealing to sterilization exceeds the process regulations, increasing the initial bacterial count; exhaust operation fails to meet the temperature and time requirements of the process simultaneously; sterilization temperature and time are below the allowable range of the process.

2. Case Study

For example, the case of "5.5 Vacuum-packed Boiled Vegetables Molding" on page 114 of "Food Quality and Safety Case Analysis":

Soft-packaged boiled vegetables (contents include: bracken, mountain celery, bamboo shoots, carrots, mushrooms, etc.), PH value 4.2-4.4. Phenomenon: The solid matter of the product is moldy, the contents soften when gently touched by hand, and shaking turns it into a pulp of fruit and vegetable juice, but there is no bag swelling phenomenon. Sampling analysis revealed the presence of a large number of molds, which are killed when heated above 70 degrees Celsius.

Reasons for microbial exceeding standards, leading to incomplete sterilization:

1. On-site management, such as raw materials being stored for too long after selection, and the randomness of water flow rinsing is very large. The interval time between upstream and downstream processes exposed to air is too long;

2. Some products have long processing times, and exposure to air may cause bacterial growth;

3. Arbitrary operation of sterilization, with the phenomenon of untimely sterilization (some products have a long time interval from vacuum packaging to sterilization, and products that have not been sterilized are exposed at room temperature, such as 30 degrees, for too long, which may cause incomplete sterilization; there is a phenomenon of shortening the sterilization time.