Hydrogen swells

Cans may sometimes swell as a result of chemical action. In high-acid foods, hard swells are often hydrogen swells, which result from the release of hydrogen gas by the action of food acids on the iron of the can.

These hydrogen swells can often be distinguished from microbiological spoilage since the appearance of swelling occurs after long periods of storage and the rate at which the can swells is usually very low.

If hydrogen is produced into the can headspace, the process is called rapid electrolyte detinning. Electrolyte action is accelerated by oxygen and by the coloring matter (anthocyanins) of red fruit. Cans affected with hydrogen swell may show varying degrees of bulging form flipping to blowing. If the tin punctured, there is emission of hydrogen gas, which is colorless and burns on the application of a flame.

Products traditionally involved have been fruits (e.g. pineapples and pineapple juice, tomatoes, peaches), but canned vegetables such as mushrooms, green beans, spinach and carrots have also demonstrated this problem.
Hydrogen swells