The proper way to do it would be to pour the contents of the can into a glass bowl, covering the top in aluminum foil, and suspending that bowl in boiling water - either on a stove or in an oven. I think it even takes less time that way. I was just amazed at how easy it was to do it the lazy way.
On the other hand, the temperature of the can shouldn't get much higher than boiling point (the water won't pass 212℉, but some heat will be transferred through the metal can making contact with the bottom of the pot) and there's a chance the can lining won't deteriorate at that temperature. I personally have no idea what they line these cans with in the first place so I couldn't say.
If you want to be absolutely safe, remove the milk from the can, heat it in glass, and accept the responsibility of having to clean dishes.
The proper way to do it would be to pour the contents of the can into a glass bowl, covering the top in aluminum foil, and suspending that bowl in boiling water - either on a stove or in an oven. I think it even takes less time that way. I was just amazed at how easy it was to do it the lazy way.
On the other hand, the temperature of the can shouldn't get much higher than boiling point (the water won't pass 212℉, but some heat will be transferred through the metal can making contact with the bottom of the pot) and there's a chance the can lining won't deteriorate at that temperature. I personally have no idea what they line these cans with in the first place so I couldn't say.
If you want to be absolutely safe, remove the milk from the can, heat it in glass, and accept the responsibility of having to clean dishes.