A refrigerator should be cleaned completely approximately once a month. The best way to clean your refrigerator is to start at the top and move to the bottom. A good watchful eye throughout each month will spot food that needs to be thrown out, and spills that need wiped up.
You will want to be prepared with supplies needed for the job before you start. Before purchasing cleaners and disinfectants that contain harmful chemicals, consider cleaning with a 50/50 mix of white distilled vinegar and warm water. Mix the solution in a bucket or dish pan. You will also need to fill the sink with your cleaning solution or warm water. Other items you may need are cleaning rags for washing and for drying, paper towels or coffee filters to get items that tend to cling, a large towel to place on the floor in front of the refrigerator. This will help keep the floor dry and not slippery. Also have a broom or vacuum, and mop handy to sweep the floor when you are finished. You may want to consider having an old toothbrush for small areas and to clean the seal on the door.
When doing a once a month, or annual cleaning of your refrigerator, its best to remove everything, including removable shelves, door racks and drawers. With a safe cleaning solution, such as the 50/50 mix of vinegar and water, and rags, start wiping down from the top to the bottom. This way as you wipe off any food and grime, it will fall as you wipe. By removing the drawers and their racks, if your refrigerator has them, you can get any food droppings or dog hair that may have blown in and stayed behind the drawers, and/or items that spilled into grooves and cracks.
After you have cleaned the inside of the refrigerator and the door, wipe the seal on the door clean, especially the top where dirt and dust collects. Wash the groves of the seal all the way around the door. If your refrigerator has a water line in which water can be obtained from the outside of the refrigerator (or for an automatic ice maker) in the front, outside of the door, it's also a good time to change your water filter. Most water filters require changing once a month.
Wipe the entire inside of the refrigerator with a dry towel or paper towels to dry the inside. If you have small pieces of food sticking to the inside of the refrigerator, and paper towels are merely pushing them around, try a dry coffee filter to remove them.
Fill the sink with dish washing detergent and hot water or a safe, chemical free cleaning agent or disinfectant cleaner to wash each individual rack, drawer, and shelf you have removed. Be careful not to put cold glass shelves into very hot water. Using harsh chemicals on your shelves and drawers may come in contact with the food you eat.
Dry all refrigerator parts you have removed completely, and replace them back into the refrigerator. Organize the shelves for a more convenient use. To help refrigerator drawers stay cleaner longer, line them with clean paper towels. As they become dirty throughout the month, simply replace them until you do an annual cleaning.
Replace any foods you have removed, but check all expiration dates on bottled and boxed items. Throw out any that have expired. Consider recycling anything before tossing in your garbage. Most glass and plastic bottles can be recycled if washed and the label is removed.
As you replace the remaining items into the refrigerator, organize it so that similar foods are together, and that vegetables and fruits are in the appropriate drawers (if you have drawers or bins).
Place a new, open box of baking soda in the back of one of the shelves to help keep the refrigerator smelling fresh. Each month replace the box with a new one. You can also remove smells by placing dry, unused coffee grounds in an open container inside your refrigerator. Each month repeat the thorough cleaning and your refrigerator will stay clean, safe, and organized.
After you have completely cleaned the inside of the refrigerator, consider pulling the unit out from the wall or space it is in. Vacuum or sweep any dirt and dust that is behind the refrigerator, underneath it, and including any coils. This will help keep the refrigerator running efficiently and give it a longer life. With a mop and cleaning solution, wipe the area where the refrigerator was sitting and allow to completely dry. Move the refrigerator back to its original location. Repeat the entire process each month.
RESOURCES:
Refrigeration & Food Safety, http://www.fsis.usda.gov/factsheets/Refrigeration_&_Food_Safety/index.asp