Grain(particularly rye and wheat) carry high loads of bacterial endospores.
If one experiences bacterial contamination problems the grain can be left to soak overnight (up to 24 hours) before pressure cooking to allow bacterial endospores to hatch.
If you let it soak too long, the grain itself will eventually start to germinate, which is not desirable. This can particularly be the case, if the temperature at which the jars are left is high, for instance in the summer. In this case itīs better to reduce the soaking time to around 12 hours.
Google search on the subject of bacterial endospores.
