springs outward. This defect is due to microbial or chemical action. It is a critical
d. Sweller. This is a can that has both ends distended at the same time.
Depending on the amount of internal pressure, the swelling may be subdivided into soft
swells, hard swells, and buckled cans. The can ends on a soft swell can be depressed
with the thumbs, whereas the ends of a hard swell and buckled cannot be depressed.
When this swelling is due to microbial or chemical action, it is a critical defect. Swellers
are not critical defects when found in coffee, baking soda, baking powder, or other items
that are known to swell and still be fit for human consumption.
e. Buckled. A buckled can is a variety of sweller, with so much gas formation
(developed during processing) that the countersink is permanently distorted. See
Figure 2-7. The buckling in cans may rupture a hermetic seal and relieve the pressure,
but the distortion of the countersink remains. A buckled can is also known as a "peaked
can." It is a minor defect if the end seam is not involved. It is a major defect if the
distortion extends into the end seam. Laboratory testing is required to determine if the
reason for the defect is chemical or biological action or a processing defect.
f. Collapsed Can. This self-descriptive defect is caused by extreme external
pressure during the come-up (pressure increase) period of retorting or by excessive
Figure 2-7. Buckling, a buckled can.