For years, the market has been developing new methods for extending the shelf life of ­pastries, snacks and sweets as long as possible – from innovative preservatives to protective gases and antimicrobial packaging materials. Yet, many companies underestimate an ­essential factor: the impermeability of their packaging.

Packaging protects pastries and sweets from numerous negative influences: this ranges from microbial growth and oxidation through to moisture and vermin. But, what happens if the packaging is not sealed well enough and leaks occur?
If moisture penetrates into chip packets or other snack foods, they lose their crispness and the product quality falls. Moisture is also damaging for pastries, as well as semi-dry products, such as pizza, because it promotes mould formation and means that food spoils more quickly. Leaks allow oxygen to penetrate, leading to oxidation, which causes fats and oils to become rancid.

Product residues in the weld seam or in an incompatible adhesive quickly lead to fine capillaries in the packaging. The consequences are goods with less flavour, which spoil long before their actual expiry date, or which even present health risks for the consumer. This leads to complaints and a poor image for the producers. As a result, they have a great interest in reliably testing the impermeability of their packaging.

These days, there are numerous methods for testing the impermeability of air-tight packaging for peanut snacks, chocolate bars, etc. The following provides an overview of the most common methods.

The water bath method is suitable for packaging with protective gas or with air under atmospheric pressure and, in some cases, also for vacuum packaging. The acquisition costs are rather low, and the principle is very simple: the packaging filled with a gas is immersed under water. The pressure involved means that part of the gas escapes from any leaks, which is shown as visible bubbles. This also enables the rudimentary localisation of leaks.

However, the method has its limits when detecting microleaks. In addition, certain type of leaks, such as fine, long capillaries, can prevent the gas from being discharged within the test period, and therefore lead to a better test result than is actually the case. Of course, the quality of the test also depends on the attention of the human tester.

Gas-based methods are used to test for leaks in packaging with protective atmospheres or air under atmospheric pressure. To perform the test, the packaging is filled with test gas. The tester creates a pressure difference between the inner and outer packaging so that the gas escapes from any leaks. The gas concentration can then be measured. Gas-based test methods are suitable for detecting microleaks. Other benefits are the short measurement duration and the non-destructive methodology.

The same advantages are also displayed by the rising pressure method, which is also used for packaging with protective gas or air under atmospheric pressure. The tester places the packaging in a foil chamber which then is evacuated rapidly. The gas flows through any leaks into the chamber, at which point the increased pressure can be measured and the leak rate calculated.

An important advantage, compared to the other test methods, is the reliable large leak detection: in case of a large leak, in many methods, the gas already completely escapes during the pressure build-up. A pressure difference is therefore no longer measured during the subsequent testing – this means, for example, that packaging with a large tear is erroneously declared to be impermeable.

The leak detector Contura S400 of the testing technology specialist Inficon is based on the rising pressure method and can therefore detect large as well as fine leaks. It operates without test gas and is completely non-destructive. This means that the system can easily be integrated into any quality assurance process.

Every company, every product and every packaging are different. Pastry and sweets producers therefore need to define their requirements in detail in order to decide on the specific leak test method that is right for them. A number of different aspects must be taken into account. The most important one is the leak rate. The acceptable leak rate for the testing can vary significantly – for example, between the rate for products that spoil quickly and the rate for food with a long shelf life. The impermeability requirements naturally need to be stricter for the former.

The objective requirements of the testing can also differ: does an absolute statement need to be made on the impermeability, does a specific leak rate need to be demonstrated, or does a leak need to be localized? Companies must consider whether a non-destructive method is more appropriate, since, in some circumstances, a product that has been tested in a water bath can then no longer be sold. This loss is negligible in the case of occasional random
sampling, yet, if entire lots are to be tested, a non-destructive test is essential.

The opportunity to detect very small as well as large leaks is also rele-vant for producers. Ultimately, many packaging materials and processes can cause both types of leaks. Modern quality management also requires tests to deliver reproducible results at any time – which is certainly not the case with a water bath.

Finally, attention also needs to be paid to aspects such as ease of use, flexible applications (inline or offline) as well as the investment and the ongoing costs. Choosing the appropriate test method is not that easy, but the effort pays off. Pastry and confectionery producers can always take advantage of the experience that has been gained in this sector by Inficon. Besides individual advice, the company also provides the right equipment for the leak testing of packaging for sweets and savoury treats.