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Self-heating food packaging is
active packaging
The terms active packaging, intelligent packaging, smart packaging and connected packaging refer to packaging systems used with foods, pharmaceuticals, and several other types of products. They help extend shelf life, monitor freshness, display inf ...
with the ability to heat food contents without external heat sources or power. Packets typically use an
exothermic chemical reaction. Packets can also be
self-cooling. These packages are useful for military operations, during natural disasters, or whenever conventional cooking is not available. These packages are often used to prepare main courses such as meat dishes, which are more palatable when hot.
Chemistry
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The source of the heat for the self-heated can is an
exothermic reaction
In thermochemistry, an exothermic reaction is a "reaction for which the overall standard enthalpy change Δ''H''⚬ is negative." Exothermic reactions usually release heat. The term is often confused with exergonic reaction, which IUPAC defines ...
that the user initiates by pressing on the bottom of the can. The can is manufactured as a triple-walled container. A container for the beverage is surrounded by a container of the heating agent separated from a container of water by a thin breakable membrane. When the user pushes on the bottom of the can, a rod pierces the membrane, allowing the water and heating agent to mix. The resulting reaction releases heat and thus warms the beverage which it is surrounding.
The heating agent and responsible reaction vary from product to product.
Calcium oxide
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, Caustic (substance), caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime (material), lime''" co ...
is used in the following reaction:
: CaO(s)+ H
2O(l) → Ca(OH)
2(s)
Copper sulphate Copper sulfate may refer to:
* Copper(II) sulfate, CuSO4, a common compound used as a fungicide and herbicide
* Copper(I) sulfate
Copper(I) sulfate, also known as cuprous sulfate, is an inorganic compound with the chemical formula Cu2 SO4. I ...
and powdered
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
can also be used, but this process is less efficient:
: CuSO
4(s) + Zn(s) → ZnSO
4(s) + Cu(s)
Anhydrous
calcium chloride
Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide.
Ca ...
is often used as well. In this case, no chemical reaction occurs, instead the
heat of solution
In thermochemistry, the enthalpy of solution ( heat of solution or enthalpy of solvation) is the enthalpy change associated with the dissolution of a substance in a solvent at constant pressure resulting in infinite dilution.
The enthalpy of sol ...
is generated.
Commercial heat sources for self-heating food packaging use an exothermic (heat releasing) reaction, for which there are several common formulations. These include:
*
Quicklime
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime''" connotes calcium-containing inorganic ma ...
aka calcium oxide, and water. Quicklime, inexpensive and readily available, is generally recognized by the FDA as safe. The product of the reaction is calcium hydroxide.
* Finely powdered magnesium metal alloyed with a small amount of iron, and table salt, actuated by adding water, as in an
MRE
A Meal, Ready-to-Eat (MRE) is a self-contained, individual field ration in lightweight packaging purchased by the United States Department of Defense for its service members for use in combat or field conditions where other food is not avail ...
flameless ration heater
A flameless ration heater (FRH) is a form of self-heating food packaging included in U.S. military
Meal, Ready-to-Eat (MRE) rations (since the early 1990s) or similar rations, capable of raising the temperature of an entrée (main course) by ...
.
Some newer formulations use a
Thermite
Thermite () is a pyrotechnic composition of metal powder and metal oxide. When ignited by heat or chemical reaction, thermite undergoes an exothermic reduction-oxidation (redox) reaction. Most varieties are not explosive, but can create brie ...
-like reaction between a more
reactive metal powder such as aluminum or magnesium, with a less reactive metal oxide such as iron oxide or silicon dioxide
Design
Self-heating
cans have dual chambers, one surrounding the other. In one version, the inner chamber holds the food or drink, and the outer chamber houses chemicals which undergo an
exothermic reaction
In thermochemistry, an exothermic reaction is a "reaction for which the overall standard enthalpy change Δ''H''⚬ is negative." Exothermic reactions usually release heat. The term is often confused with exergonic reaction, which IUPAC defines ...
when combined. When the user wants to heat the contents of the can, a ring on the can—when pulled—breaks the barrier which keeps the chemicals in the outer chamber apart from the water. In another type, the chemicals are in the inner chamber and the beverage surrounds it in the outer chamber. To heat the contents of the can, the user pushes on the bottom of the can to break the barrier separating the chemical from the water. This design has the advantages of being more efficient (less heat is lost to the surrounding air) as well as reducing excessive heating of the product's exterior, causing possible discomfort to the user. In either case, after the heat from the reaction has been absorbed by the food, the user can enjoy a hot meal or drink.
See also
*
Beverage can
A drink can (or beverage can) is a metal container designed to hold a fixed portion of liquid such as carbonated soft drinks, alcoholic drinks, fruit juices, teas, herbal teas, energy drinks, etc. Drink cans are made of aluminum (75% of w ...
*
Flameless ration heater
A flameless ration heater (FRH) is a form of self-heating food packaging included in U.S. military
Meal, Ready-to-Eat (MRE) rations (since the early 1990s) or similar rations, capable of raising the temperature of an entrée (main course) by ...
References
Further reading
* Yam, K.L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009,
External links
Single-serving coffee can heats itself*
BBC News Online
BBC News Online is the website of BBC News, the division of the BBC responsible for newsgathering and production. It is one of the most popular news websites, with 1.2 billion website visits in April 2021, as well as being used by 60% of the U ...
Hot drink can tested in MidlandsAn article with photos on disassembly
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Food packaging
Canned food
Containers
Food storage containers
Serving and dining