Bam: examination of metal containers for integrity

The quality of a food container is determined by its ability to protect the product it contains from chemical deterioration or microbiological spoilage. Good double and side seams are essential to agood hermetic seal, particularly at the cross-over (juncture); however, the performance of a can is also affected by many other factors. Spoilage within the can may be caused by leakage,underprocessing, or elevated storage temperatures. Leaker spoilage occurs mainly from seam defects and mechanical damage. Improper pressure control during retorting and cooling operations may stress the seam,resulting in poor seam integrity and subsequent leaker spoilage. However, the rate of container defects that might result in food spoilage is usually low.

The suitability of the particular food to bepreserved also affects the performance of the container. Hydrogen swells and sulfide stains caused by chemical corrosion sometimes occur. In addition, prolonged storage of cans at elevated temperaturespromotes corrosion and may result in perforation. Improper retorting operations, such as rapid pressure changes, may cause can deformation and damage seam integrity. Postprocess contamination bynonchlorinated cooling water or excessive buildup of bacteria in can-handling equipment may also cause spoilage, and abusive handling of containers may result in leaker spoilage.

Although the incidenceof spoilage in canned foods is low, it is necessary to know how to proceed with the investigation of the integrity of the can when spoilage does occur. This chapter presents methods for seamexamination and leakage detection.

Container examinations associated with food spoilage are usually accompanied by pH determination of the product, gas analysis of can headspace, and microbiologicaltesting of the product (see Chapter 21). Analytical results that depart from normal patterns may indicate changes within the container and help to pinpoint the cause of spoilage.

The double seam (Fig....