Wine pretty much makes itself. Yeast cultures naturally grow on grape skins. You harvest grapes, smash them with a press, or stomp on them with bare feet, run it through a screen to filter out the pomace, and let the juice ferment.

Yeast was not known about in medieval times, as evidenced by the Reinheitsgebot of 1516, saying that beer can only contain water barley and hops. So it was not explicitly added as it is in modern times.

Waowh aradplaug good on you for doing your research.