We make butter from 'home-skimmed' raw milk/cream. And the milk content (which seems inevitable, as DW prefers completely skimmed milk) does seem to slow the buttering coming. Temp is the other big factor, often we take our straight out of the fridge and it'll take a full 10 min. but if it's warmer the time certainly is pared back (20'C is the target). We use the kitchen whizz on the lowest speed, works ok, but personally would rather have a 'real' (hand operated) churn if I had the opportunity. Tried washing it in the whizz as well but figured I was wasting my time (as it seemed to continually smash more fat out), so I wash the butter by hand now.