My fridge is pretty clean and I wipe up any spills in the fridge as soon as they happen or as soon as I notice them.
So my fridge is usually pretty spotless but sometimes the fridge still gets some food residue or other sticky substances in it and I don't notice until a week or even month later.
I try to wipe down my fridge when it gets near empty which is around once per month but I wipe the shelves down as much as I can once per week.
During the spring weather I empty the fridge out and take it outside and then use the pressure washer to pressure wash the refrigerator out completely.
I also then vacuum the back of the fridge as well.
Having a clean fridge is a must for your health and your families health because you can get illnesses from a dirty fridge that is dirty inside.
I also cannot stand to have my fridge dirty and I can't stand a dirty house either so I clean as often as possible.
Wipe up spills as they happen and then it won't be so hard to get the spills up.