Capable of surviving airdrops, rough handling and extreme climates, and just about anything except a GI's jaws, the new "pocket" sandwich is designed to stay "fresh" for up to three years at 26 °C (about the temperature of a warm summer's day), or for six months at 38 °C (just over body temperature).
For years the US army has wanted to supplement its standard battlefield rations, called "Meal, Ready-to-Eat" (MRE), with something that can be eaten on the move. Although MREs already contain ingredients that could be made into sandwiches, these have to be pasteurised and stored in separate pouches, and the soldiers need to make the sandwiches themselves.
"The water activity of the different sandwich components needs to complement each other," explains Michelle Richardson, project officer at the US Army Soldier Systems Center in Natick, Massachusetts. "If the water activity of the meat is too high you might get soggy bread." To tackle the problem, researchers at Natick used fillings such as pepperoni and chicken to which they added substances called humectants, which stop water leaking out. The humectants not only prevent water from the fillings soaking into the bread, but also limit the amount of moisture available for bacterial growth.
The sandwiches are then sealed, without pasteurisation, in laminated plastic pouches that also include sachets of oxygen-scavenging chemicals. A lack of oxygen helps prevent the growth of yeast, mould and bacteria.
Soldiers who tried the pepperoni and barbecue-chicken pocket sandwiches have found them "acceptable". They are now planning to extend the menu to pocket pizzas, as well as cream-filled bagels, breakfast burritos and even peanut-butter sandwiches.
The pocket sandwiches won't see action until 2004. But like dehydrated egg, freeze-dried coffee and processed cheese-all originally developed by the military-the long-life sandwich will probably find its way into grocery stores.
Author: Duncan Graham-Rowe
New Scientist issue: 13th April 2002
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