Hmm. Lumpy has not happened to me- wonder if it is because of the boiling? I raise my milk to 160 or so, then cool immediately- it never actually boils. I think it is technically "scalded" milk. I have used both ultrapasteurized and low temp pasteurized whole cow millk for mine- every once in awhile it does come out runny. I suppose I could strain it, but I think of it as my version of the commercial "go-gurt" they sell to the kids as drinkable yogurt.