The History of Brewing
Brewing was known to the early Chinese, the Mesopotamians, the Egyptians and the Babylonians. As best as we can make out, most of these early brews involved thick porridge-like mixes of grain and water that had been left out for wild yeast. The resulting 'beer' was probably not particularly tasty, but alcoholic. Big news, but sadly came some of the worst hangovers of the ancient world.
It has only been relatively recently that the agent of brewing (yeast) was actually understood to be any part in the brewing process at all. Many of the old recipes call for you to simply put the ingredients into a barrel previously used for the purpose and wait. It was not known what it was that magically caused the alcohol to form in the brew.
Obviously, brewing still worked - mainly because the grapes often carried the wild yeasts upon them, but also because the residue of the previous brews would still be embedded within the grain of the oak casks.