If I leave a bowl of milk (after cereal) out, a few days later it solidifies and turns into something resembling yoghurt.
What is it, exactly?
And what happens if you eat it?
You may have yogurt. You should have went for cheese curds. Sour cream is useful too. What you have depends on what grew in the milk.
You have fermented milk, but you’ve allowed it to ferment with a wild culture of bacteria. Commercial fermented milk products (yoghurt, cheese, creme fraiche) control the end result by introducing a carefully selected culture of bacteria.
(in the case of cheese, there is also a curdling process that is performed before fermentation)
You made something that is to yoghurt what sourdough bread is to ordinary bread.