I didn't notice that the goat milk yogurt I made tasted more sour than usual yogurt but acidophilius does produce lots of acid. Maybe you could find a live culture milk product, maybe kefir that has several types of bacteria. The sheep milk yogurt I buy has live culture S. thermophilis, L. Bulgaricus, L. acidophilis and Bifidus. Contaminants can always be a problem if the milk is not brought to a boil or if the yogurt maker is not sterile. You could try using 100 proof vodka to sterilize the yogurt maker after scrubbing it out thoroughly.