Many of the foods that last for a long time are high in sugar and salt.
很多保质期很长的食物都含有很多糖和盐。

In simple terms, they draw water out, so if bacteria try to grow on it, they will simply shrivel up.
简单讲，这是因为它们能把水分吸出来，所以如果细菌尝试在上面生长就会失水变干。

This is why we use salt to make ham, sugar to make jam, and both to make gravlax.
也正是因为这个，我们才会用盐来制作火腿，才会用糖来制作果酱，才会同时用这两种东西来制作渍鲑鱼片。

As foods in their own right, if salt and sugar are stored away from moisture in airtight containers, they will last indefinitely.
而盐和糖作为食物本身来讲，如果能存放在隔绝水分的密闭容器里，它们就能够保质到天荒地老。

But additives, such as iodine added to salt, can reduce its shelf life to about five years.
但是，盐里面的食品添加剂，比如碘，则可能把它的保质期缩短至五年。

（翻译：能猫）