Heat Seal Integrity - Implications for Manufacturers and Retailers

In a project funded by WRAP, a team from the University of Lincoln investigated the contribution that inadequate heat sealing of food packaging might make to the generation of food and packaging waste in the supply chain and the household; the generation of increased costs and potential for consumer complaint.

Using accepted testing methods heat seal integrity was measured in 11 factories containing 105 heat sealing units, packing a variety of ambient, fresh, chilled and frozen foods, and the team found that poor seal integrity could be a major cause of food and packaging waste. Whilst about 24% of packs measured exhibited seal problems judged liable to cause leakage problems in the factory, distribution chain, retail outlet and/or home, only 1% of packs were judged sufficiently damaged by factory tests to be rejected by the factory quality testing systems.

During the seal testing process, it was found that the most common quality check used in the factories was the simple but inadequate 'manual squeeze test'. It was estimated that up to 480,000 tonnes of food waste per year could be generated through the production and lack of detection of unsound heat seals, and findings showed that the most frequent reason for seal failure was product contamination in the seal area and that sealing problems were more common where products had liquid and crumb components.

Looking ahead, it was anticipated that achieving adequate heat sealing would become a greater problem as new packaging materials such as PLA (polylactic acid) and packaging lightweighting are introduced more widely. The team identified some 'best management practice' procedures which could reduce waste generation but concluded that to achieve major improvements, technological changes were required in packaging design, machinery design, packing systems and seal integrity measurement.

These technological improvements should include better filling and heat sealing methods to reduce product contamination of the seal area and the development of robust in-line seal monitoring systems and associated control systems.