A lot of food likely was, but as @moortaktheundea points out, fermentation is so ubiquitous in nature, it was probably stumbled upon, and shortly after, people started to refine the hell out of it. Even more so than a creative species, we are a tinkering species. “Hey, that fire thing is useful. How do I get it without waiting for a storm, and how do I keep it around without burning down a forest?” You see a bird weaving a nest, and using a stick to poke bits through holes, so you start tinkering with bits and bobs of sticks, bones and siniews until you end up with a needle.
Even the most deliberative tools went through multiple iterations from the natural (oh! that rock is sharp!) to the manufactured (my flint knives will cut through even the sharpest hides! don’t be caught with an imitation, insist on Grog’s genuine knapped knives, today!). Why would food be different?
