Guide to Inspections of Low Acid Canned Food 47.
Manufacturers - 2
occur. These are swollen containers and seam defects. Seam defects are covered in part 3 of this lacf Guide-Containers/Closures (will issue at a later date).
Swollen Containers - Swells can occur in metal containers, plastic pouches, plastic trays or tubs. Swells in glass containers are less likely to occur because hermetic seal of the lids (caps) depends on a vacuum. Swells result from gas production which would eliminate this vacuum. Side seal lids would come off the jar without a vacuum. Threaded or twist-on lids would remain on the jar, but would lose their hermetic seal. Most threaded or twist-on lids have a panel in the center which loses its concavity with loss of vacuum. Plastic pouches would tend to balloon. Plastic tray covers would swell. Cans exhibit various degrees of swelling. These are known as hard swells, soft swells, springers and flippers. The definitions for these are as follows:
- Flat (normal) - a can with both ends concave; it remains in this condition even when the can is brought down sharply on its end on a solid, flat surface.
- Flipper - a can that normally appears flat; when brought down sharply on its end on a flat surface, one end flips out. When pressure is applied to this end, it flips in again and the can appears flat. Flippers result from a lack of vacuum.
- Springer - a can with one end permanently bulged. When sufficient pressure is applied to this end, it will flip in, but the other end will flip out.
- Soft swell - a can bulged at both ends, but not so tightly that the ends cannot be pushed in somewhat with thumb pressure.
- Hard swell - a can bulged at both ends, and so tightly that no indentation can be made with thumb pressure.
Gas production, and resultant swelling, may be caused by chemical reaction or by bacteria which may or may not produce toxins. Improper cooling can also buckle cans creating the appearance of hard swells. In addition, a severe body dent can cause a lid to 'bulge'. Most can experts can determine the difference between hard swells and buckles. Proper pressure control during can cooling is necessary to prevent buckling from occurring. Can sizes of 303 x 406 or smaller usually do not require pressure cooling.
Swelling due to overfilling will only result in flippers or springers. If these are the only abnormal cans found, check fill control, headspace control, or other attributes which may result in little or no vacuum in the containers.
The presence of microorganisms in processed containers can result from various causes such as post processing entry through flexing seams, out-of- specification seams or seam defects. Under- processed containers would allow survival of microorganisms which could result in spoilage. Swelling due to thermophilic organisms was discussed previously under can cooling.
Swelling due to overfilling will only result in flippers or springers. If these are the only abnormal cans found, check fill control, headspace control or other attributes which may result in little or no vacuum in the containers.
Another cause of swelling is a chemical reaction of the product with the metal in the can. This usually results in the production of hydrogen gas. Overfilling of the can may also cause some degree of swelling.
Because there is no way of determining toxin presence non-destructively, all swollen cans must be considered a potential health hazard and sampled. Typically, any lots with a swell rate in excess of 1% are considered to be adulterated, and subject to seizure or detention regardless of the cause.
The lot should be held and a sample collected in accordance with Attachment 13, Sampling Schedule for Canned and Acidified Foods. Also reference IOM Section 427.1-Field Exam and 450-Sampling: Preparation, Handling, Shipping.
"A Complete Course in Canning", Books I,II,& III, Anthony Lopez, 12 Edition, 1987. The Canning Trade, Baltimore, Md.
"Advances in Batch Retorts for Food Processing (Water Trickle and Air-Steam Retorts for Processing lacf)" Unpublished, Michael D. Ellison, FDA 1989
"An Introduction to Thermal Processing of Foods" The AVI Publishing Company, Westport, Connecticut, S.A. Goldblith, M.A. Joslyn and J.T.R. Nickerson
"Canned Foods, Principles of Thermal Process Control, Acidification and Container Closure Evaluation," 1988, The Food Processors Institute, Washington, D.C.
Code of Federal Regulations, Title 21 Part 108 "Emergency Permit Control", Part 113 "Thermally Processed Low-Acid Foods Packaged in Hermetically Sealed Containers" and Part 114 "Acidified Foods."
"Continuous Rotary Sterilizers Design and Operation" Bulletin 44-L, First Edition, National Food Processors