A lot of fermented stuff like bread, cheese, wine and beer most likely started as "stuff forgotten in a pot" - not very complicated. In case of bread you need: two stones for milling the grain, a pot to mix it with water and store it, and then a fire to bake it. Not medieval tech, but way earlier.
Beer has been known since at least the bronze age, there are recipes known today, but the initial stage was, yet again, mill some grain, mix with water, forget in a pot.
Wine: forget some fruit in a pot.
Source: Reading history, plus my ADHD brain keeps forgetting stuff in the kitchen. I accidentally invented soda one of these days, because sometimes the forgotten stuff gets fizzy, too (you do need to invent the hermetically closing jar for that though, open clay pot doesn't work in that case)!
Btw one of my crazier theories (although I'm not the only person considering it) is that it wasn't us domesticating the world, but that we were domesticated by yeast. So it was inevitable that we kept producing vessels and feeding the fungus with sugar in ever more refined ways. Fungus wants to grow.