Originally Posted by gusd

Not quite correct. First, flights to OTP leave from the B gates (most of the time bus gates), not Z gates. The official Z to B transfer requires a train ride and clearing security, though no passport control. This route may be tight with 60 minutes. If the OP has an EU passport, one can avoid security by clearing passport control into A, using the tunnel to B, and clearing passport control again in B. This is usually faster. See my report on this in this post.

Also, flights from the US don't always arrive at Z gates, either. They sometimes arrive in B. Unfortunately in FRA planes arrive at the gate where they are needed for their next departure, so clean vs unclean country is not always a good indication of whether one needs to clear security or not.