bread that does not get moldy
It's the baking and packaging.

These dark rye breads are baked for a very long time (effectively pasteurizing them) and then sealed in their packaging. If you do this in a commercial setting that can ensure a mostly contaminant-free environement, such breads can last a long time.

Once you break the seal by opening the pack, your bread will get moldy like all other breads.



The very dense crumb structure and compounds in the whole-grain rye used might to a certain degree inhibit the growth of mold, but not enough to make the bread last for months.