You need to make sure that the culture is stable before you use it -- it should smell sour, but with no other foul smells. In the first week of a new starter, y

You need to make sure that the culture is stable before you use it -- it should smell sour, but with no other foul smells. In the first week of a new starter, you shouldn't use it because the bacterial cultures are still fighting for dominance. As for mould build-up, that isn't a good sign. It does happen and I know people who just scrape off the mould and move on with their lives but I'd personally start again from scratch.