Soon-to-be cultured milk with fresh fruit safe for consumption?

Recently my cousin started to make yogurt. She told me that she puts diced, fresh fruit (strawberries, peaches) into the inoculated milk (pasteurized or sterilized, I don't know. ¹) and then let this set in the oven at ~50°C for some hours. After this, she puts the yogurt into the fridge. She makes enough yogurt for ten days; on the tenth day she takes the last yogurt portion and makes some new.

At the first thought I couldn't imagine that fresh fruits stay safe for ten days (I wouldn't eat cut fruits that stayed for ten days in the fridge!). But after some pondering I wondered if it's safe after all because the milk and the fruits are going to be cultured and undesired bacteria are going to be eliminated. I think freshly diced fruit only contain bacteria on the surface.

¹ I saw a really big jug of milk. She lives in Georgia, US. I don't know what's the common treatment of milk there.

Best Answer

Not only are "friendly" bacteria being cultured, those bacteria make an acidic environment which is hostile to "bad" bacteria.

Myself, I make plain yogurt and mix things into it at the time of eating, but things mixed in from the start essentially become "yogurt-pickled" and should be fine for a reasonable period under refrigeration. A standard part of preparing to culture yogurt is a high-heat treatment (scalding) of the milk, both to kill off unwanted bacteria and to cause structural changes in the milk proteins that are beneficial to forming the yogurt curd.