Rancidity is caused by oxidation of fats upon exposure to air. It is not a bacterial or fungal rotting. It can be prevented by packing jerky or other meats containing some fat in an air-tight container without a lot of excess room around it. Indians used to pack pemmican in large blocks into tight skin sacks and the jerky and added fat would keep for years. Of course, the meaty part of jerky could still rot from bacterial or fungal action but soaking it with brine or sugar will inhibit that.