Ensuring the seal integrity of modified atmosphere packaging using high-speed laser detection technology

As the world moves to a post-COVID new normal, let's not forget about the challenges food producers faced with unexpected worker shortages, new procedures and even new regulations. All these challenges drive the need for digitalization and automation in the food factories. In the highly competitive food and beverage market, gaining an advantage with the customer begins with better control of packaging lines. Not only do improved packaging processes translate into increased production and operational efficiency, but they also mean greater customer satisfaction as food and drink stay fresh longer.

Most consumers who shop at their local supermarket judge foods based on the physical appearance of the food like uniform fill levels, firmly closed caps, dents or firmness of the packaging, instead of checking for micro leaks in the packaging that might indicate spoilage or contamination.

Leakage does not necessarily mean product spilling out; it is often more subtle like reduced shelf life and food spoilage when specialized gas inside the packaging escapes. Once oxygen enters the packaging, it can accelerate the growth of aerobic bacteria, mold and speed of food spoilage. Carbon dioxide (CO₂) added into the packaging, displacing oxygen, drastically decreases reactivity, allowing ingredients to retain freshness and remain stable for a longer period.

This is true especially when modified atmosphere packaging (MAP) is used to improve shelf life and freshness. MAP options such as nitrogen and carbon dioxide are used for fresh or cooked meat packaging and shredded or sliced cheese packaging.

If the package is not fully sealed, either through an incomplete sealing process or a puncture, problems may arise like mold or shorter than labelled shelf-life, which will have a detrimental impact on the food company’s brand and reputation.

In the pursuit of operational excellence

Packaging assembly lines often run up to hundreds of items per minute, so any leak detection method must be able to keep up with the production. It has to be significantly more accurate than labor-intensive traditional methods where a random package is taken from the line and submerged in water to detect escaping bubbles. This is not an accurate method because it will most likely miss most of the leaks in the packages that do make it to the store shelves. If a leak is found, the line must be stopped, and operators have to hunt through the process to determine where the problem is.

Whether they dunk random individual or batches of packages, this time-consuming test method in water has another drawback which is product wastage as soggy packaging cannot be sent to the stores and gets thrown out.

Another method which is less wasteful and messy, puts each package or group of packages in a sealed chamber and exerts a controlled vacuum on the interior. If there is a leak, the chamber will not reach the prescribed negative pressure level. There are several drawbacks to this method:

• The chamber must be sealed completely to avoid a false positive.
• There’s no way to identify a single leaking package in batch checks.
• There must be enough free gas inside the package to affect the overall pressure.
• A start/stop action of the conveyer is required.
• There must be enough time scheduled for the gas to escape through a small leak.

Finding the right method to test for leaky packaging is a key challenge for a food producer. Every producer hopes to find a method that can test each package for seal integrity that is accurate, automated and fast enough and to avoid slowing down the high-speed packaging lines.

Quickly detect leaks reliably

A technology that has gained growing acceptance in the food and beverage industry for detecting CO₂ leaks is quantum cascade laser (QCL) technology (Figure1). It is particularly effective in CO₂ leak detection as the technology uses CO₂’s ability to absorb specific wavelengths in infrared (IR) light. The laser sends a beam covering a narrow range of IR wavelengths across an open space to a detector. A weakening of the critical wavelength that is greater than the overall output indicates the presence of CO₂. The degree of impact to the wavelength indicates the concentration. As CO₂ is the most commonly used MAP gas, a QCL dectector is a very useful tool for leak detection. A QCL detector can also act very quickly, allowing for 100 percent seal integrity, checking at an incredible speed of 200 packages per minute.

Figure 1: QCL analyzers use infrared light to determine the presence of CO₂. Photo courtesy of Emerson.

Steps to achieving speed and accuracy

The sophisticated methodology and mechanisms that go into an effective tool for CO₂ detection include the following:

• Packages pass through a purpose-built arch or hood over the conveyor.
• Air is drawn at a consistent rate through the arch and the QCL analyzer element.
• The laser pulses on for less than one millisecond, allowing more than one laser to be used at nearly the same time. Fast pulses are called “chirps”.
• Sequential firing of lasers allows detection of up to four gases at any one point in time.
• Even the smallest whiff of CO₂ can be detected as a package passes under the arch.
• A rejection mechanism is triggered by the control system, pushing the package off the conveyor belt, aligned with the speed of the conveyor.

Details of the mechanism vary and change according to the type of packaging. A bottle of beer will more likely push CO₂ out, given the nature of the beer (Figure 2), but a package of meat will need a gentle squeeze to release measurable CO₂ (Figure 3). The adjustment can be built into the system while still maintaining a production speed of about 200 packs per minute.

Figure 2: A QCL system, such as Emerson’s Rosemount™ CT4215 Packaging Leak Detection System, detects trace gases from defective packs, including bottles in cartons. Photo courtesy of Emerson.

The QCL system is customizable to accommodate a range of package sizes and types, including cartons, kegs, trays, pouches, bags, cans and bottles. An alarm stack-light can be programmed to flash for each rejection or an issue indicator that requires attention. The system can be programmed to trigger a line shutdown if a high number of rejects have been identified.

Figure 3: Emerson’s Rosemount CT4215 Packaging Leak Detection System makes it very easy to identify an incomplete seal in modified atmosphere packaging. Photo courtesy of Emerson.

As mentioned earlier, CO₂ is not the only gas used for MAP. QCL system can detect as little as 20% of CO₂ in MAP to detect any leakage. Other gases and vapors are detectable using QCL by changing the laser to one capable of transmitting at a different frequency. A winery or distillery, for example, can use QCL to detect ethanol leakage from bottles or barrels.

Case studies from the plants

Keeping draft beer from arriving flat

North America’s largest brewery used the QCL solution to ensure their draft beer kegs were fully sealed before shipment to bars and restaurants. Initially, they used an in-line optical camera test solution, but it cannot provide the required degree of accuracy. It gave too many false positives and false negatives. After installing Rosemount CT4215 Packaging Leak Detection System, the plant saw a significant level of improved accuracy and reduced package leakage and waste with better product quality. After the initial success, the company is on track to outfit all its keg lines worldwide with the QCL system.

Reducing waste for meat packers

Immersion leak testing methods are used in various food packaging plants. The heavily manual process in meat packaging has remained in use because there is no suitable alternative method that can accommodate the different package sizes or volume of product that moved through. Large plants can have 30 or more packaging lines. The immersion method, however, is unreliable as they just have a random test sampling of packaging from the lines, which is thrown out afterward. The consumer will more likely be the one to find the leaking package after they come home with their purchase from the grocery store.

As a trial test, one plant installed a single Rosemount CT4215 Packaging Leak Detection System to perform 100 percent of inspections on a critical packaging line and ran it alongside their regular manual water immersion tank inspections. It allows the company to identify 1.5 percent of its production that otherwise would be wasted. The company found that many of their improperly sealed packages could be recovered because they were discovered quickly without immersion. A quick calculation across the plant output of 20 million pounds per year meant a yield of 300,000 pounds of recovered “free” products.

Consistent, Accurate and Reliable

In the new post-COVID world, a fast, in-line QCL-based leak detection system provides a reliable and repeatable solution to package inspection challenges, enabling food producers to effectively leverage the digitalization and automation technologies to ensure 100 percent inspection of packaged products.

Image caption: iStock.com/jenoche