I've tried to made home-made yogurt. I've tried to follow the receipt first by pasteurizing milk to kill the bacteria, waiting until the milk is 107 degree and adding culture. I've used incubator for 4 h (as indicated on culture pack).
I've got a rather sour cream at the bottom and the rest was soured milk. While I don't mind it and I haven't drank it in ages that wasn't what I was looking for.
Either you failed to adequately pasteurize the milk, or your culture was bad, or some unclean / unsanitized (some would say sterilized, I know better) utensil was involved on the cooling/inoculating side of the pasteurization step.
4 hours is a remarkably short incubation time - were you aiming for a "liquid/drinkable" yogurt? For a set yogurt 8-12 hours is typical and my process at this point is 24 hours at a somewhat lower temperature (95-100F) as I like the result better than the warmer/shorter incubation.
