Among the latest weapons designed by the US military is a sandwich which has been designed to stay fresh for up to three years, according to a report in this month's New Scientist.
The "indestructible" sandwich will be capable of surviving airdrops, and extreme climates, remaining fresh for up to three years at 26 °C, or for six months at 38 °C (just over body temperature).
The "pocket" sandwich has been designed as a meal that can be eaten by US forces while on the move, and is an addition to the current "Meal, Ready-to-Eat" (MRE) rations available to the US army.
Although MREs already contain ingredients that could be used in 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," said 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."
Researchers used fillings such as pepperoni and chicken and added substances called humectants, which prevent water leaking from the ingredients. The humectants aid freshness by stopping water from the fillings soaking into the bread, but also by limiting 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". The researchers 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 will not feature in ration packs until 2004, but like freeze-dried coffee and processed cheese which, according to New Scientist, were originally developed by the US military, the long-life sandwich has a potential place on supermarket shelves.