I know I'm bumping an old thread with some information that you may already have, but...
I got to this web-site (
http://www.uni-giessen.de/gloning/tx/sawe.htm) by looking up the name "Sabina Welserin" that was attached to an old recipe someone posted on one of these threads. Apparently it's from 1553, so that's definitely pre-whatever.
It's in "frühneuhochdeutschen" which I believe means early new high German. The challenges in reading this are that the spellings are not modern (e.g. wirst used instead of wurst) and often not consistent (prattwirst and brattwirst in the same recipe, both wirst and wúrst.used).
My wife, who's first language is German, read a bit and then stopped in disgust. The difficulties are even worse for English speakers. I speak a little German so I understood some of it, but I like European languages and I'm pretty persistent.
On the other hand... it's free.
Dort wo man Bücher verbrennt, verbrennt man auch am Ende Menschen. - Heinrich Heine.