How to Check the Seal Quality of Food Packaging
A packet of chips looks perfectly sealed until someone opens the carton and finds half the packets have lost their crunch. Sometimes, the problem starts with a tiny gap along the sealed edge. Air gets in, the food loses its freshness, and the whole batch may be rejected.
That’s why food factories need to regularly check their packaging seals. A seal may look fine on the outside but still have a leak. It helps workers catch problems just before the packed food goes to the customer.
How to Check the Seal Quality of Food Packaging Before Products Leave the Factory
There isn’t one test that works for every package. A plastic pouch filled with spices needs different checks from a tray of fresh chicken.
The type of packaging film, sealing temperature, pressure, and food inside the pack all matter. Here are seven ways factories can find weak seals.
1. Start by Looking at the Sealed Edges
The first check doesn’t need expensive equipment. Pick up a freshly packed product and examine its edges.
Look for these problems:
- Small wrinkles running through the seal
- Food crumbs or powder caught inside
- Corners that haven’t closed properly
- Burnt or melted plastic
- Uneven sealing marks
For example, a little flour trapped in the seal of a snack pouch can stop the two film layers from joining properly.
Looking at the seal helps, but it won’t catch every leak.
2. Pull the Seal Apart to Check Its Strength
A peel test shows how much force it takes to separate the sealed layers.
The workers take a sample of the package and put it in a testing machine. The machine pulls the two sides apart while measuring the force.
If the seal opens too easily, something may be wrong with the heat, pressure, or packaging materials.
A seal shouldn’t be so strong that customers struggle to open it either. Manufacturers need a strength that suits the food and the package.
3. Test the Seal While It’s Still Hot
On a busy packing line, sealed packets don’t always get much time to cool.
They may move straight from the sealing jaws onto a conveyor belt. If the seal hasn’t formed properly, it could open before the material cools.
A hot tack test checks how well the seal holds together at this stage.
This test matters particularly for factories running high-speed filling and sealing machines.
4. Check How Much Pressure the Package Can Handle
Think about packets stacked inside a shipping carton. The ones at the bottom carry pressure from everything above them.
A burst test helps workers see how a package behaves when pressure builds inside it.
During the test, air pressure increases until the package or seal fails.
“This result enables manufacturers to compare packs and identify potential vulnerabilities.” It doesn’t tell the whole story, though, because the size and shape of the package also affect the reading.
5. Use Water to Find Hidden Leaks
Some leaks are too small to spot by looking at the packet.
In a bubble test, workers place a sealed package in a testing chamber under water. The chamber reduces the surrounding pressure.
If air escapes through a hole or poorly sealed edge, bubbles may appear.
This makes it easier to find where the leak is coming from.
Not all types of packaging are suitable to this method but many sealed pouches and air filled packs can be tested.
6. Try a Coloured Dye Test
A dye penetration test is another way to find small gaps.
The worker introduces a coloured testing liquid along the seal and watches whether it passes through.
If the dye travels across the sealed area, there may be an open channel.
This method can be used by factories in checking flexible film packaging solutions or investigating repeated seal failures.
The tested sample cannot go back into the food supply.
7. Measure Pressure Changes Inside the Package
Some leaks are difficult to find even with water or dye.
Pressure decay testing looks for pressure changes under controlled conditions. A leak may cause the measured pressure to fall.
The test equipment records the change so workers can compare it with the accepted limit.
For certain packaging types, gas flow testing can also help measure leakage.
Why Do Food Packaging Seals Keep Failing?
Finding a weak seal is only half the job. The next step is working out what caused it.
A few things are worth checking:
- Too much heat: The packaging film may become damaged.
- Too little heat: The film layers may not join properly.
- Low sealing pressure: Parts of the seal may remain open.
- Food inside the seal: Oil, powder, or crumbs can get between the layers.
- Worn machine parts: Damaged sealing jaws can leave uneven marks.
Workers should also check whether the film suits the machine and the packed product.
Keep Checking Seals During Production
Don’t rely on one sample taken at the beginning of the shift.
Check packs regularly, especially after changing film rolls, adjusting machine settings or changing products.
In factories with traysealers and thermoforming machines records should be kept of rejected packs and test results.
Staff training also matters. Workers who know what a poor seal looks like can catch problems before hundreds of packs are affected.
Regular technical service and timely replacement of spare parts can avoid the machine to have repeated faults.
Food Packaging Machines and Sealing Support from Ilpra
Ilpra supplies food packaging equipment, including tray sealing and thermoforming machines, for different packing needs. Businesses can explore equipment options based on their food products, packaging materials, and production requirements. Checking film compatibility, arranging machine maintenance, and testing sealed packs remain important parts of daily production.
Frequently Asked Questions
1. How can I check whether food packaging is sealed properly?
Look for gaps, wrinkles, and trapped food particles. Use leak testing to check for hidden problems.
2. What causes food packaging seals to leak?
Wrong sealing temperatures, low pressure, damaged film, and food caught between the layers can cause leaks.
3. Which test finds small leaks in food packaging?
Bubble leak testing, dye penetration testing, and pressure decay testing can help find small leaks.
4. Why does packaging film fail to seal properly?
The film may be unsuitable, the machine settings may be wrong, or the sealing surfaces may be dirty.
5. How often should food packaging seals be checked?
Check them throughout production and whenever workers change packaging materials or machine settings.
