It is not heated because the high sugar content prevents spoilage. Although it is often hard to find, the label has a stamped date code which indicates the date by which it should be consumed. Sweetened, condensed milk may thicken and darken as it ages, but it is still edible. Shelf Life of Canned Milks Unopened cans of evaporated milk can be stored on a cool, dry shelf for up to six months. Check the date on sweetened, condensed milk for maximum storage.
Some areas have difficulty storing metal canned goods for long periods of time.
This is usually caused by very high humidity or exposure to salt in a marine environment. If this is a problem, it is possible to extend the life of metal cans by coating their outsides. I've seen this used on boats here in Florida, especially when loading for a long trip. Using a double boiler, paraffin is melted and brushed on the clean, unrusted cans. Be certain to get a good coat on all seams, particularly the joints.