Forcing an insert instead of an update

I have a has_many association that I wish to append records to.
However, what happens instead is that the first row inserted gets
updated in place thereafter. The way I am creating this append row is
this:

current_log_entry = current_entry.ca_customs_edi_log_entries.build

This is then saved when the related row in the parent table is saved.
How do I force an insert rather than an update for rows after the first?