Robots for automated packing of jars and cans
Introduction
A lid that does not seal properly is one of the most common problems when filling food into jars. The consequences range from vacuum loss and reduced shelf life to customer complaints or even product recalls.
The good news: In most cases, the cause is not the capping machine itself. Often, it is the interaction between the lid, jar, product, and process settings that determines whether a seal is secure.
In this article, you’ll learn what causes capping problems and how to prevent them for good.
Quick answer
A lid often fails to seal properly because several factors are not optimally coordinated. These include incorrect capping torque, unsuitable lids or jars, dirty sealing surfaces, the wrong product temperature, or an incorrectly adjusted capping machine. For a secure seal, all components of the production line must work together perfectly.
How can you spot a capping problem?
Not every capping problem is immediately visible. Typical signs include:
- Loose lid
- Lid opens easily by hand
- Vacuum is missing or too low
- Product leaks after pasteurization
- Lid becomes deformed
- Safety button remains raised
- Leak-related customer complaints
The 7 most common causes
1.
Incorrect capping torque
If the torque is too low, the lid won’t be tight enough. If it’s too high, the seal may be damaged or the lid deformed.
2.
Unsuitable or damaged lids
Even minor damage to the gasket or manufacturing tolerances can prevent a secure seal from forming.
3.
Variations in jars
Variations in jar height, thread or neck diameter can significantly affect the capping process.
4.
Contaminated sealing surfaces
Product residue on the jar rim prevents the gasket from sitting flush. This can cause leaks or vacuum loss.
5.
Incorrect product temperature
Especially during hot filling, product temperature affects the vacuum formed later. If it is too low or too high, the seal may be compromised.
6.
Incorrectly adjusted capping machine
Capping heads that are not adjusted correctly or worn parts often result in inconsistent capping results.
7.
Problems throughout the production process
Not every cause is directly related to the capping machine. Conveyor speed, jar guides, or an uneven product feed can also negatively affect the capping process.
What are the possible consequences?
A faulty seal can have significant financial consequences:
- Customer complaints
- Reduced shelf life
- Loss of vacuum
- Quality issues
- Production downtime
- Increased waste
- In the worst case, product recalls
How can capping problems be prevented?
Reliable sealing starts with production line planning.
Key factors include:
- high-quality lids and jars
- clean jar rims
- correctly set capping torque
- appropriate product temperature
- regular capping machine maintenance
- continuous quality checks
- optimal coordination of every process step
When is the problem not caused by the capping machine?
In practice, the capping machine is often the first suspected cause of problems. In fact, many capping issues start earlier in the process.
Examples:
- product fill level too high
- product residue on the jar rim
- poor lid quality
- incorrect product temperature
- inconsistent jar quality
That’s why at Machines4FoodIndustry we look at the entire production line, not just one machine.
✅ Checklist: 7 things to check right away
If lids don’t close properly, check the following first:
☐ Is the correct torque setting selected?
☐ Are the lids and seals undamaged?
☐ Are the jar rims clean?
☐ Do the jars meet specifications?
☐ Is the product at the correct temperature?
☐ Is the capping machine set up correctly?
☐ Is the vacuum checked regularly?
💡 Expert tip from Machines4FoodIndustry
"Many manufacturers initially invest in a new capping machine, even though the real cause lies elsewhere. Our experience shows that capping problems usually arise from the interaction of several process steps. That’s why we always analyze the entire production line—from product feeding to vacuum testing."
- Paweł Grabiec
Managing Director, Marba Sp. z o.o.
Engineering Partner of Machines4FoodIndustry
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FAQs
Why doesn’t my lid seal properly, even with a new capping machine?
A new capping machine alone does not always solve the problem. The cause often lies with the lids, jars, product temperature, or process control.
What role does product temperature play?
During hot filling, the right temperature is essential for subsequent vacuum formation and a secure seal.
Can a damaged lid prevent a vacuum from forming?
Yes. Even minor damage to the gasket or lid can prevent a sufficient vacuum from forming.
How often should a capping machine be inspected?
Regular maintenance and inspection of the capping heads and torque help ensure consistent capping results.
How can seal quality be reliably checked?
In addition to visual inspections, torque and vacuum tests should be carried out regularly to ensure process reliability over the long term.
Lids not closing properly?
Our experts analyze your entire production line and identify the cause of capping problems—whether it lies with the capping machine, the lids, or the process settings.
Schedule a no-obligation consultation today.