A slice of prototype pizza, in development to be used in MRE's — meals ready to eat, sits in a packet next to a smaller packet known as an oxygen scavenger at the U.S. Army Natick Soldier Research, Development and Engineering Center in Natick, Mass.

They call it the holy grail of ready-to-eat meals for soldiers: a pizza that can stay on the shelf for up to three years and still remain good to eat.

Soldiers have been asking for pizza since lightweight individual field rations — known as meals ready to eat, or MREs — replaced canned food in 1981 for soldiers in combat zones or areas where field kitchens cannot be set up.



Researchers at a U.S. military lab in Massachusetts are closing in on a recipe that doesn't require any refrigeration or freezing.



"You can basically take the pizza, leave it on the counter, packaged, for three years and it'd still be edible," said Michelle Richardson, a food scientist at the U.S. Army Natick Soldier Research, Development and Engineering Center.



(Read more: 'Preppers' and their MREs)

Scientists at the Natick labs also are responsible for developing equipment and clothing that improves soldiers' combat effectiveness and their survival, but the quest for good pizza has become known as the holy grail there.



Pizza is one of the most requested items when soldiers are asked every year what they'd like to see in their rations, said Richardson, who has spent nearly two years developing the recipe in a large kitchen full of commercial equipment.



Scientists' efforts were long thwarted because moisture in tomato sauce, cheese and toppings migrated to the dough over time, resulting in soggy pizza that provided the perfect conditions for mold and disease-causing bacteria to grow.



(Read more: Old-school pizza makes a comeback)

But on-and-off research over the past few years helped them figure out ways to prevent moisture from migrating. That includes using ingredients called humectants — sugar, salt and syrups can do the trick — that bind to water and keep it from getting to the dough.



But that alone would not help the pizza remain fresh for three years at 80 degrees, so scientists tweaked the acidity of the sauce, cheese and dough to make it harder for oxygen and bacteria to thrive. They also added iron filings to the package to absorb any air remaining in the pouch.