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Testing, testing, testing

16 June 2023

John Miller discusses the use of nitrogen in packaging crisps and looks at some solutions that can be used to test for product freshness.

The air in crisp packets is actually nitrogen, and the slack-fill – the difference between the capacity of the packaging and the volume of contents therein – performs a key function.

Nitrogen is used to modify the atmosphere inside the packaging environment and is vital for keeping crisps fresh and crispy. 

Nitrogen has a highly stable triple bond that minimises reactions with the ingredients inside the packet, keeping the crisps from going stale by reducing their exposure to oxygen. Filling the packets with nitrogen helps prolong the shelf life of crisps without using chemical preservatives.

The same applies to the level of fat within the packet. Crisps are baked or fried using oil. The type of oil used varies depending upon the brand or flavour, but all oils deteriorate with exposure to air. Stale oil will taint the flavour of the crisp.

But freshness isn’t the only reason for all that space. Crisps are delicate and endure a lot of movement before their reach the consumer. Nitrogen-filled packaging can provide a cushioning effect to protect crisps during transportation and handling, helps keep them intact and distributes pressure evenly, reducing the likelihood of damage caused by compression or vibration.

So nitrogen keeps crisps fresh until consumers are ready for a snack, but how can producers ensure they are crunchy when they go into the bag? Excess moisture reduces their crunch, while too little makes crisps hard. Near Infrared (NIR) moisture gauges can be used to maintain the desired freshness and taste of crisps. These non-contact gauges emit specific wavelengths of light that interact with moisture molecules in the crisps.

The intensity of the reflected light absorbed by the water molecules depends on the moisture concentration. Crisps lacking moisture will absorb less light. By using the moisture gauge to accurately and continuously measure moisture content, it is possible to adjust cooking times and temperatures accordingly to achieve a consistently high-quality product, all without physically touching or damaging the crisps.

The fat content in crisps also helps determine quality and shelf-life. Fat content can be measured using equipment such as the InfraLab Food Analyzer, based on the principle that the oil on a crisp will absorb and reflect NIR light. By calculating the intensity of the reflected light, the oil can be quickly, accurately and continuously determined. This process also enables brands to display the fat amount on their packaging and substantiate ‘low-fat’ claims with evidence.

Packaging integrity
Packaging plays a crucial role in maintaining the freshness and taste of crisps. Even with the correct oil and moisture content, crisps will quickly stale and lose their taste if the packet is compromised, and oxygen is able to enter. Through pressure decay or vacuum testing methods, it is possible to identify even the smallest of leaks to ensure crisps remain fresh.

With vacuum testing, a sample of packets is selected from the production line and placed inside a sealed vacuum chamber, which isolates the contents from the surrounding atmosphere. A vacuum pump then removes air, causing the packets to slightly expand. From here, manufacturers can scrutinise the sample for leaks or flaws, including shape irregularities, alterations in pressure or packet collapse.

John Miller is Managing Director at LIMAB UK.


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