Packages that Heat and Cool Themselves

During the 1950s and ’60s, when I was busily inventing and developing all sorts of innovations that were to eventually influence all food technologists and food industry professionals, I chanced upon a concept of thermoelectricity that could sequentially heat and cool its proximity. Using a principle of thermocouple and reverse thermocouple, a device could heat when direct current was flowing in one direction and cool when it was flowing in the opposite direction. I instantly applied for a patent (but never pursued it), engineered a small refrigerator-oven for installation aboard airliners and space vehicles (yes, in those days, space ships were carrying astronauts who wanted to eat real food), and published a paper in Food Engineering about it.

As seems too often to be the case with pioneering innovators, my ideas were premature. Not until much later were nonmechanical, silent, thermoelectric heating/cooling devices engineered for hotel rooms. Using very little energy, thermoelectrics could sequentially heat and cool practically on battery power—if reliable batteries had existed. And thermoelectric principles might have been applied to self-heating and -cooling packages, but they were not—then.

Rather, resistance wires were imbedded into package structures and plugged into nearby electrical sources to produce the earliest self-heating packages. Obviously, self-heating in those times meant connection with a power source, a bit awkward for those who wanted to wander off the beaten track.

Traditionally, military field rations were eaten cold—I don’t long for the days of using my bayonet to open a can of ham and lima beans to consume in a snow-covered copse. And then came the revolutionary notion of igniting cans of Sterno jellied alcohol over which the open food cans could be placed to overheat the base and permit the top layers to remain cold. Yummy. Food packaging technologists working for the government then were charged with developing packages that would heat without benefit of electricity, which is usually not available in the field.

Self-Heating Packages
And simultaneously, food packaging technologists in civilian life began their search for self-heating packages that could be employed anywhere, especially away from homes and restaurants. Optimistic marketers believed that self-heating packages would have universal appeal, while pragmatists identified substantial niche markets, including the military, campers, hikers, sail boaters, and drivers and their passengers.

The first—and apparently still the best—of these self-heating packages took advantage of the exothermic properties of calcium oxide exposed to water. Sufficient heat is generated by the reaction to elevate the temperature of anything in proximity to acceptable eating level. Sometimes, without careful package engineering, the temperature was too high for immediate consumption.

• Japanese Developments. Japanese packaging suppliers developed a host of self-heating packages that employed the calcium oxide exothermic principle to heat water for coffee—which the beverage packager thoughtfully supplied—along with sugar and powdered cream. The entire kit was within a thermally insulated cup about twice the size of a conventional coffee cup. The consumer, trapped in his automobile in early morning Tokyo traffic, would dispense water from a contained pouch into the cup and spill some more water into the interior liner of the cup to react with the calcium oxide. Within minutes, the water would be hot enough to dissolve the instant coffee, which could be blended with the sugar and cream to help overcome the stressful situation. Passengers, meanwhile, could heat their saki in cans making use of the same lime–water reaction prior to sipping. One supposes that today, Japanese motorists percolate their coffee, brew their tea, or heat their bottled saki in electrically powered mini-devices plugged into the battery of their Toyotas and Hondas—after removing their cell phone charging cable, of course.

• Military Rations. Military developers determined that calcium oxide reactions were not rapid enough for fast-moving soldiers, so magnesium oxide was substituted in flexible pouches—with the usual addition of water to actuate. The speed of heating was sufficient to warn users that they could burn their fingers and tongues on the package or its contents.

• HeaterMeals. As interesting as self-heating packages were, they hardly dented the American scene until some enterprising entrepreneurs at HeaterMeals Inc., Cincinnati, Ohio (phone 513-772-3066), developed an add-on for retort-trayed meals. A second tray containing the exothermically responsive inorganic iron plus magnesium salt was placed externally to and beneath the sealed retort tray. “Salt water” would be added to a pad on the base tray from a conveniently enclosed pouch, and within 15 min the contents of the retort tray would be heated to acceptable serving temperature. Another commercial niche product for campers and truck drivers had been born.

In addition, more than 200 million units of the company’s Zesto Therm water-activated “flameless ration heater” have been used by the U.S. Army for heating MRE (meal, ready-to-eat) field rations since 1990. The system raises the temperature of an 8-oz food pouch by 100°F upon activated by addition of 2 oz of plain water.

• Ontro Cans. Receiving much more publicity has been the can patented by Ontro Inc., Poway, Calif. (phone 619-486-7200), which also employs exothermic reactions to heat contents such as soup, pasta, coffee, tea, and hot chocolate. The calcium oxide and water are in two separate adjacent cylindrical chambers within the can. After inverting the can, the consumer punctures the heating device by pushing on a puck that breaks an internal aluminum-foil seal to release the water from its container into the calcium oxide to generate the heat. A third closed fluted chamber designated an “internal heat generation cone” retains steam and helps conduct heat to the surrounding food contents. Within 5 min of activation in the upright position, the temperature of the contents is elevated to consumption temperature, a maximum of 75°F above initial ambient temperature. The external polypropylene is said to maintain the temperature of the contents elevated for 20 min.

Cans are multilayer polypropylene/ethylene vinyl alcohol for oxygen and moisture barrier plus heat resistance. Polypropylene is the plastic of choice to provide a package material that can resist boiling water temperatures, the highest temperature being limited by the water confined in the can. The can size is a 16-oz 211 3 606 can with a content capacity of 10 oz.

In addition to its newer developments on trays and pouches, Ontro is proposing to work with military food packaging developers on self-heating group ration technology.

• Beverage Partners. Another entrant in the self-heating can competition is Crown Cork and Seal through Beverage Partners, a Nestlé–Coca-Cola joint venture aimed at canned coffee and tea. Although technically satisfactory, the extra cost is regarded as too significant at present.

Obviously, the cost of the devices adds to the basic package cost. More important, the space volume and weight (about 3.5 oz for what would otherwise be a 2-oz can) of any of the exothermic reaction devices is cited as a deterrent to mainstream application—to date.

Self-Cooling Packages
And then there are the self-cooling packages from other companies. The Joseph Co., which may no longer be in business, received top honors at the Cannex exhibition in 1997. The principle was the same as employed for so many mechanical refrigeration systems: evaporation of fluorocarbon liquid. The can contained a closed internal chamber that, when punctured, would release the liquid as a gas with the latent heat of evaporation removing heat from the contents and cooling it by about 30°F for a 500-mL can. Because of environmentalist objections to the release of fluorocarbons into the atmosphere, the internal coolant was switched to carbon dioxide gas activated by charcoal.

Crown Cork and Seal Co., Inc., Philadelphia, Pa. (215-698-5100) is reported to have offered a self-chilling can for Coca-Cola, probably developed by Tempra (941-739-8900). The technology appears to be a desiccant that sucks heat from the beverage through a gel-coated evaporator and into an insulated heat-sink container. The beverage company has stated that it has not yet found a niche for this can in a market that is highly price sensitive.

Cooling may also be achieved by endothermic reactions such as dissolution of ammonium nitrate and ammonium chloride in water followed by shaking—not a recommended procedure for chilling cans of carbonated beverages or beer—when the consumer demands his or her beverage cold.

Another starter is Instacool™ from CoolCan Technologies, Inc., Calabasas, Calif. (866-266-5226) whose technology is based on a carbon dioxide cartridge which, when the can opening tab is pulled, triggers the capsule to release gas in snow form to cool the contents within less than one minute.

The Future
Notions of self-heating and self-chilling packaging have excited investors and marketers alike over the past two decades. Successful Japanese applications have not translated into products on American shelves. Technically viable technologies have not become commercial—yet.

Resistance to innovation in food packaging is hardly uncommon when cost is factored into the equation. On the other hand, daring innovation is a hallmark of food packaging technology. Just because I am enamored with battery-powered thermoelectric technology as holding potential for the future does not mean that my University of Georgia food packaging students were not on a correct track with their water-activated calcium oxide self-heating pouch term project last semester. Perhaps the niche is wide enough for both—and for self-chilling.

PRODUCTS & LITERATURE
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by AARON L. BRODY
Contributing Editor
President and CEO, Packaging/Brody, Inc.
Duluth, Ga.