hullo,
I get raw milk from a farm near me -- when it is fresh from the cow then it isn't sour/bitter, and the only difference from shop milk is you get cream around the top!
Sometimes I leave it to separate to get the whey out, at which point it is a little sour, and after this it will slowly go bitter -- It is no problem though - I always drink/eat it like this and I'm still fine! ;-)