Honey, you remember that friend of yours who always talked about melting horses? Apparently, he's some sort of billionaire now and I'm leaving you for him.
All jokes aside, I imagine cremating horses was the preferred method of disposal. I'm sure no one wanted to dig holes big enough to bury a horse. I wonder if that's how it was discovered.
See also: the first guy who looked at an udder and thought "I wonder what will happen if I yank on those bad boys JUUUST right" or "look at that calf just sucking away like it owns the world! I want some of THAT action!"
Women have tiddies we can suck on and we know milk comes from there. Seeing a calf nurse can have us assume we can get milk that way. A + B means we can get milk from bovine that way.
Yeah, but what would make him WANT that milk? It's not like any humans except babies had been drinking milk until then and cows, though adorable, are not the cleanest animals..
Beer makes even less sense. How thirsty do you have to be to look at a container of rotten wheat water, to decide that maybe that water is clean enough to drink?
Wine at least makes a bit of sense since I'm pretty sure that vinegar predates wine. Beer though? Nope.
One of the theories on alcohol is mead (honey wine) was the first alcohol. Supposedly hunters would throw a bit of honey into their water skins and go hunting. When they came back, they might not have finished it and when used again, it was alcoholic. Eventually they noticed the effect and enjoyed it.
I'm sure after that much experimentation was had on different carbohydrates.
Beer seems hard though. You have to boil it just right to make it right, before you even start fermentation.