The metal exposure test on beverage cans is a quality control measure that tests the interaction between the inner lining of the can and its contents. This test is important because the inner lining of a can is designed to protect the metal from the product it contains, which may be corrosive or reactive. If the coating is insufficient or defective, the product could react with the metal, causing contamination and possible health risks to consumers, as well as compromising the integrity of the can.

The metal exposure test consists of filling the cans with a saline liquid to control the reaction of the cans with this liquid. The current (measured in milliamps) through the can is proportional to the exposed metal surface, indicating the degree of porosity of the coating. If the values are too high, it suggests that the internal protective lacquer may not be adequately coating the metal surface, which could result in exposure of the metal when the can is filled with the actual beverage.

If a can fails this test, indicating that the metal is excessively exposed to the test liquid, production can be stopped and monitored to identify and correct the problem. This could result in extensive losses in terms of downtime and spoilage, but is considered necessary to avoid even greater losses that could occur if the problem is not detected and resolved.

Metal exposure testing is part of a broader set of quality control measures to ensure that beverage cans meet the necessary safety and performance standards before they are shipped to customers and filled with beverages.