Exothermic reaction is used as heat source. Such product can be very useful for military operations, during natural calamities, for mountaineers, and whenever conventional cooking is not possible.
During World War II (1939-1945), some food cans had wicks on them, like candles have. The wicks were attached to an inside tube. When soldiers lit the wick, the tube heated the food.
It relied on the burning of cordite (a smokeless propellant consisting of 65% gun cotton, 30% nitroglycerin and 5% mineral jelly) to provide thermal energy, a design that could hardly be considered safe in untrained hand.
Self-heating Food Can is usually a two chambered Can, one for food and one for heating unit. The heat is generated by an exothermic chemical reaction, water. The heating unit is contained in either an outer chamber surrounding the food, or an inner compartment immersed in the food or drink.
Newer self-heating cans are easier to use. Just push a button. The button breaks a seal inside a heating cone. Water and limestone combine in the cone, releasing heat. Three minutes later the content of food or drink is hot.
The recent designs have all relied on an exothermic chemical reaction to generate heat; in most cases; the reaction is between CaO (quicklylime) a water-based solution. In military purpose, meals-ready to eat (MRE) programs using highly reactive exothermic reactions based on magnesium oxidation or the reaction between potassium permanganate and glycerin has created a niche but growing market for self-heating food product for emergency services and the outdoors sector.
Self-heating cans have been commercially available for decades and are particularly popular in Japan for sake, coffee, tea and ready meals.
Kita Sangyo started producing self-heating can in 1986. Pushing the bottom button makes a reaction of lime (CaO) and water (H2O), which generates a very safe heat. The content, such as alcoholic beverage, etc. is wormed up at about plus 40 degrees Celsius in about 5 minutes.
Self-Heating food packaging
