Remember caffeinated beef jerky? The newest member of the military's Meals Ready to Eat (MRE) family is an ultra-durable sandwich that can be served fresh after sitting on the shelf for two years. Hungry yet? Here's how food scientists managed to stall Father Time — at least in a sandwich bag:

Why a sandwich?
Why not? The "freeze-dried dreck" that constitutes most MREs has to last years at a time while supplying hurried soldiers with the energy they need, says Clay Dillow at Popular Science. And most of these air-sealed meals, typically little more than "gummy paste," are in dire need of an upgrade. Enter "the world's most cutting edge sandwich." 

So what keeps it fresh?
"For food to rot, you usually need oxygen and water" to invite in bacteria, says Will Shanklin at "MREs that eliminate water have great shelf life, but horrible taste." In order to keep these high tech sandwiches flavorful, scientists enlisted the preservation properties of a familiar condiment: jam. 

What does the jam do?
Unlike freeze-dried food, preservatives like jam have high water content, says Shanklin. The high-tech sandwich's jam-like filling — whether it tastes like PB&J or an Italian-style hoagie — "locks in the moisture," creating a barrier around the water molecules that bacteria need to survive. A special "packet of iron fillings" is also inserted into the package, which "draws in excess moisture, converts it into rust, and traps it." As for oxygen? The sandwich is packed tightly and vacuum sealed, like most other MREs.

And do soldiers like it?
"I'm a big fan. I love the bread," one soldier tells BBC News in a TV interview. Another echoes his sentiments: "It's definitely the best two-year-old sandwich I've ever had," he says, smiling. "Better than a lot of new ones I've had, too." 

Sources: BBC NewsGeek.comPopular Science