On a per capita basis, food waste costs the U.S. economy more than $200 billion per year, according to a white paper released by the American Institute for Packaging and the Environment (AMERIPEN), St. Paul, Minn. With the many ways in which food is lost or discarded – from harvest through consumption – it’s no wonder that food spoilage and waste are considered significant sustainability concerns.
Advances in packaging technology play a critical role in minimizing food waste by preventing the ingress of microorganisms, oxidation and moisture, all of which have an adverse effect on shelf life. While many food manufacturers that use flexible packaging aim to thwart these threats by choosing the right film and establishing appropriate sealing parameters, there is another, often overlooked, part of the equation—how airtight the package is.
Package leaks can stem from a variety of issues, including large pores in the film that can develop from overstretching. Fine, difficult-to-detect capillaries can also form if product residue gets caught in the weld seam or if an incompatible adhesive is used. Reliable leak detection technology can help food and packaging machinery manufacturers catch compromised packages before they reach the consumer.
Choosing the right leak detection equipment is a critical part of that process. Here are three primary methodologies:
The water bath method, also known as a bubble test, has been used for several decades due to its simplicity. A test package is submerged in water, and if there are leaks in the package, the gas will find its way toward them and escape, creating visible bubbles in the water. If the water bath works as intended, the tester can make a general assumption about how airtight the package is.
Unfortunately, there are many shortcomings of the water bath method in practice. One challenge is that leaks often found with food packaging cannot be reliably identified in a water bath due to their leak rate. For example, leaks caused by insufficient welding seams are not often large enough to be easily recognizable using this method. Other drawbacks include the risk of simple human error – that the bubbles in the water bath are overlooked – and that tested products cannot be sold and must be discarded.
With these methods, testers create a pressure difference between the inside and outside of a package. Tracer gas, which, in the food industry, is usually either carbon dioxide or helium, will escape through any detected leaks and its concentration can be measured.
However, using carbon dioxide as a test gas also creates challenges. Among them is the fact that manufacturers can only test products that have a certain proportion of carbon dioxide content. Depending on the gas-based device being used, the range is usually between 10-20%. In addition, when using gas-based testing for flexible packages, there is a risk that pouches will burst if the interior and exterior pressure rates are significantly different.
- Pressure increase in a flexible test chamber
With this method, a package is placed between two unique membranes to create a conformal vacuum chamber that is then quickly evacuated. The gas flows through any package leaks into the chamber where it causes an increase in pressure. The test is completely non-destructive and all results are reproducible.
A significant advantage of this method vs. alternative approaches is its ability to safely detect micro and gross leaks. When leveraging other methods and a large leak occurs, the gas completely escapes during the evacuation process and no pressure difference can be measured. As a result, a package with a tear or a non-welded sealed seam might be incorrectly identified as airtight.
Choosing the right method
There are a number of variables that impact which leak detection method is best suited for a particular application. What kind of package will be tested? Is a non-destructive test required? Does the packaging contain protective gas or sufficient head space? What leak rate is acceptable, and can it be quantified? This last question in particular is important as rates can vary widely between perishable products such as cheese and foods with longer shelf lives.
Food manufacturers should seek out suppliers that can help determine which leak detection method is best suited for them. Taking these steps are an efficient and accurate way to determine if hermetically sealed packages are airtight and ensure that consumers receive products that are fresh, safe and will not spoil prematurely.