Thanks to some unknown inventor, self-heating cans first appeared around 1900 for use by mountaineers and explorers. The most common versions involve a can with two chambers—one for the food and one for the heating unit. The heat is generated by an exothermic (heat-producing) chemical reaction between calcium oxide (quicklime) and water.
The heating unit is contained in either an outer chamber surrounding the food, or an inner compartment immersed in the food or drink. It is activated by pressing a button or poking holes to break the seal between the water and quicklime. The reaction heats up within a few seconds, and heats the food inside the can in minutes.
During World War II, Heinz manufactured self- heating beverages with a cordite stick down the center that heated the contents when lit, but they were not always reliable. Legend has it that the first recorded casualty of the D-day invasion of Normandy was a British soldier whose self-heating meal exploded, covering him in tomato soup when he tried to light the cordite stick.
More recently, some companies have revived the concept. In 2002, Nescafe tested a self-heating coffee can in the United Kingdom, but found that the can did not heat the liquid to a consistent temperature. In the United States, celebrity chef Wolfgang Puck began selling self-heating coffees and lattes in 2005, but had to recall them the next year after they failed to heat evenly, or in some disturbing cases, exploded or melted. It seems that the world may have to wait a few more years for this food of the future.
