Found it on a Swedish site.
Fit vinum et ex aqua ac melle tantum quinquennio ad hoc servari caelestem iubent. aliqui prudentiores statim ad tertias partes deco**** et tertiam veteris mellis adiciunt, deinde XL diebus a canis ortu in sole habent. alii diffusa ita decumo die obturant. hoc vocatur hydromeli et vetustate saporem vini adsequitur, nusquam laudatius quam in Phyrigia.
That's the original latin.
I'm gonna translate the Swedish translation. :P
A wine made from just water and honey. For this rainwater that's been saved for five years is recommended. Others that are knowledgeable use rainwater as soon as it's fallen and boil it down to a third and add a part of old honey to third parts water. Let the mix stand in the sun for 40 days after Sirius rise. Others take it after nine days and seal it. This drink the Greek call "hydromeli" and with time it will taste like wine. It's appriciated the most in Phrygia.
The recipe is from 77 AD, written by Plinius the Elder.
Anyone wanna try it? :P
There were some other old recipes, I might re-translate them later. A bit too tired right now.