Mouldy food suggests that your worms may not be eating scraps quickly enough. The worms should start working on scraps within a few days and finish them within 1 to 2 weeks. If you spot mouldy food in your worm farm, it is best to remove it. You may then need to reduce the amount of food scraps that you are adding.

It is best to start with a small amount of food scraps (about a handful every few days). The worm population will grow gradually and as the population grows, they will eat more! You can increase the amount of food scraps that you add as this happens. 

It would be best to remove the excess food to prevent it rotting and then add scraps at a slower pace until their appetite increases.