Gaseous swelling or 'bloats' in evaporated milk cans is caused by gas-forming, spore-forming anaerobic bacteria that survive the sterilization process. Clostridium foetidum (and Clostridium sporogenes / Clostridium thermosaccharolyticum) produces large volumes of carbon dioxide and hydrogen gas along with foul putrefactive odors, causing the can ends to bulge or bloat.

Option analysis:

• Proteus ichthyosmius: Incorrect. A non-sporing organism associated with fishy taint in milk.
• Staphylococcus epidermidis: Incorrect. Non-sporeforming skin flora that cannot survive thermal sterilization.
• Bacillus subtilis: Incorrect. An aerobic sporeformer that typically causes sweet curdling or flat sour spoilage without significant gas bloating.
• Clostridium foetidum: Correct. A putrefactive, gas-producing obligate anaerobe causing bloated cans in evaporated milk.