TROUBLES WITH TIN CANS
To discover pin-holes or any leaks in a tin can, immerse it in boiling water after sealing and if there is any bubbling from the can, you may rest assured it needs resealing.
Swells in tin cans are caused by insufficient sterilization. The action of bacteria causes gas to form in the can and as a result there is a bulging at either end. If left alone long enough the cans will explode. Watch carefully all bulging cans and use them first. Sometimes a slight bulge occurs when a can has been filled too full.
If you have trouble sealing tin cans the chances are that the can is too full. See that no particle of food touches the top or when soldering, if you employ that method of sealing, small pin holes will be blown in the seal by escaping steam which is generated by the hot sealer coming in contact with the cold food. Another cause of sealing trouble lies sometimes in a poorly heated capping steel or because it is not kept brightly tinned. To make a proper seal the steel must be kept bright, hot and clean.
Also, be sure you buy good solder as there are inferior grades that are too poor to flow when properly heated.
FROZEN PRODUCTS
Watch all jars and cans that have been subjected to a freeze. If the cans or jars do not burst the only harm done is a slight softening of the food tissues. In glass jars after freezing there is sometimes a small crack left which will admit air and consequently bacteria.
Sometimes cans and jars tip over in the wash boiler during sterilizing. This is caused by using a false-bottom which is too low or because it is not well perforated. Or it may be due to the fact that the jar was not well packed and so may be too light in weight.