How to tell if the food in a vacuum bag has gone bad?

Opening the fridge, you find that the meat bag sealed in a food vacuum bag last week is puffed up like a little inflated balloon. Could it be that the vacuum wasn't properly applied during the sealing process, or has the food quietly "spoiled" in the sealed environment? Holding this "puffed-up" vacuum bag, you feel it's a pity to throw it away, yet you're afraid of getting sick if you eat it. Actually, a swollen vacuum bag isn't definitely a sign of spoilage, but it might indeed be a "health warning" from the food. Today, we'll scientifically analyze the reasons behind the swelling and teach you simple ways to determine if the food is still safe to eat.

1. The "Duality" of Food Vacuum Bag Swelling: Distinguishing "Physical Swelling" from "Bacterial Spoilage"

The core principle of vacuum packaging is to inhibit the reproduction of microorganisms by removing air, thereby extending the shelf life of food. However, when the bag swells, there may be two completely different mechanisms behind it, and we need to first learn to distinguish between them:

 "Physical Swelling": A "Normal Phenomenon" Not Indicating Spoilage
This type of swelling is not caused by food spoilage but is mostly related to environmental changes or packaging details. For example, when refrigerated food is taken out of the fridge, the small amount of residual air inside the bag expands when heated, causing the vacuum bag to swell slightly. Or, sharp-edged or boned foods (such as ribs, fish pieces) may puncture the bag with their sharp parts during storage, creating tiny gaps that allow outside air to slowly seep in, resulting in "pseudo-swelling". This kind of swelling usually occurs slowly, the bag swells evenly, there is no unusual smell when you get close to it, and the color and texture of the food itself are basically the same as when it was sealed, so it generally does not affect consumption.

"Bacterial Swelling": A "Spoilage Signal" That Requires Vigilance
This is the situation that needs the most attention. When food spoils due to improper sealing, excessive storage time, or poor temperature control, spoilage bacteria (such as Escherichia coli, Salmonella, etc.) will multiply in large numbers inside the bag. During their metabolism, they produce gases such as methane, carbon dioxide, and hydrogen sulfide, causing the bag to swell rapidly in a short time, and you can even feel a obvious "bloating sensation" when touching it. This kind of swelling is often accompanied by an unusual smell, which is a clear sign of food spoilage and should be discarded without hesitation.

2. A Two-Step Judgment Method: Decoding Food Freshness with "Smell" and "Sight"

After the vacuum sealing bag swells, if you want to further confirm whether the food is spoiled, you don't need complex tools. You can accurately judge by "smelling" and "looking":

1. Smell the Odor: Capture the "First Signal" of Spoilage

Odor is the most sensitive "early warning device" for food spoilage. The moment you open the vacuum sealing bag, hold your breath and sniff gently:

If you smell a distinct sour smell, rotten smell (such as the fishy smell of meat, the sour smell of rice and flour), or a "rancid smell" from fatty foods, it means that bacteria have multiplied in large numbers, and the food has spoiled. Be sure to discard it directly and do not try to eat it.
If the odor is similar to that when the food was fresh (such as the faint meaty smell of meat, the natural fragrance of dried foods) and there is no abnormal odor, you can proceed to the next step of observation.

2. Observe the State: Identify Signs of Spoilage from "Color" and "Texture"

Spoilage bacteria not only produce gases but also change the physical properties of food. By observing the color and texture, you can further confirm:

Abnormal color: The surface of meat turns grayish, green, or has irregular black spots; vegetables lose their bright color, turn yellow, become soft and mushy, and exude water; dried foods (such as fungus, mushrooms) have mold spots on the surface, clump together, and become sticky. These are all typical signs of spoilage.

Abnormal texture: Meat becomes sticky, loses elasticity, and cannot rebound after being pressed; fruits become soft and mushy, oozing juice, and there is mucus at the broken parts of the peel; grains (such as rice, flour) clump together and have mold spots. Even if there is no obvious odor, they may have been contaminated by mold and are not recommended to be eaten.

If the color and texture of the food are basically the same as when it was fresh (such as frozen meat that does not change color or have mucus after thawing, and dried foods are dry and loose) and there is no abnormal odor, you can comprehensively judge based on the storage time and environment (such as whether it has been refrigerated at low temperature throughout the process). If confirmed to be okay, you can eat it as soon as possible.

3. Exploring the Root Cause: Why Do Vacuum Bags Swell? How to Reduce "Abnormal Swelling"?

The essence of vacuum bag swelling is either "infiltration of external air" or "gas production by internal bacteria", and both situations are closely related to packaging operations and storage details:

If the machine has good sealing performance, the bag mouth is clean and free of oil when sealing, there are no leaks after sealing inspection, and the food is stored within the specified shelf life and in a low-temperature environment, the vacuum bag is usually not easy to swell.
On the contrary, if the sealing is not tight, the food itself contains a lot of moisture or impurities, or the storage temperature is too high (such as a refrigerated environment above 4°C), it may lead to bacterial growth or air infiltration, causing swelling.

Therefore, the key to reducing abnormal swelling of vacuum bags lies in standardizing operations (ensuring tight sealing and dry food) and controlling storage conditions (refrigerating at low temperature and avoiding long-term storage) to reduce the risk of spoilage from the source.

The swelling of a vacuum bag is the result of the "interaction" between food and the environment. It is like a mirror, reflecting both the sealing performance of the packaging and revealing the freshness of the food. Learning to distinguish between "physical swelling" and "bacterial swelling" and using the simple methods of "smelling" and "looking" to judge can not only avoid wasting food due to misjudgment but also keep the bottom line of food safety. After all, when faced with "suspicious" food, "it's better to discard it than to take the risk" is the most responsible choice for your health.