All cans intended for food use are lacquer coated to prevent any acid to metal reaction. Reaction product maybe beneficial in small amounts. Some metal elements are needed by the body but too much is cannot be handled and deemed harmful.
How to detect cans with defective lacquer? Such will allow unwanted reaction. In worse case scenario, just opening the container will tell. The food has disagreeable odor and flavor. Or, open the can, transfer contents to another container and inspect the inner walling. Any discoloration is a sign of defective coat.
What if the coat has minute pinholes? Very small holes that are almost not visible to human eye? I did another simple test to see.
Again, I got two metal cans, one aluminum can and one tin can. Open both cans and cleaned it gently using mild soap and soft brush to minimize lacquer coating damage. Dried. Got a scalpel with a tip as thin as needle point. Then created several pinholes on bottom end of cans by gently pointing the tip against lacquer and twisting it around. Filled both cans with vinegar and covered with cellophane.
No scratches made on can walls. Reaction was expected only on bottom of the cans where the pinholes are created. Pinholes were barely visible. Another observation was made after four days.
After four days, the man-made pinholes became clear. It became wider and discolored. If the packed good is of high acid type, pinholes can be seen by opening the can, transferring the content to another container and inspecting the inner walling. Any visible dot should be suspected as pinhole. For easy open canned juices and sodas, anyone may not bother opening it completely with a knife.