There are several reasons this can happen.
- Check the food is as dry as possible before placing it into the fryer.
- Mop up excess water from washing or pre-boiled food with kitchen towel or a clean tea towel.
- Low fat oils have high water content and are not suitable for deep fryers as they can cause excessive foaming.
- Check the level does not exceed the maximum level indicated and that you are not overfilling the unit.
- Change the oil regularly. The frequency required will depend on the type of oil.