Possible Reason: Milk did not pasteurize  Solution: After pasteurization has completed, check the temperature of the milk—it should reach a minimum of 161°F / 72°C   Possible Reason: Culture added was not active Solution: If using store-bought yogurt as a starter, make sure the cultures are active probiotics   Possible Reason: Too much milk in inner pot  Solution: Run the pasteurization cycle a second time