There are several ways for bacteria to sneak into snack food packaging and other stand up bags. This commonly happens during the manufacturing process. The fault usually lies in the packaging machine and more than one package gets affected. At Standuppouches.net, we take care that this never happens.
The second known way for bacteria to get into food bags is a puncture during transportation and handling of the product. Some sellers simply re-seal the package when a puncture is detected. The bacteria usually get inside the packaging when the puncture happens, and the re-sealing does not let the gas to come out, thus causing a bloat.