Cast iron pans are old-fashioned kitchen items that still perform as well today as they did in our grandparents' time. Many people even proudly cook on a pan that belonged to a long-gone relative and swear by the results. The pans are durable and nearly indestructible. They can be used on a home range or home on the range over a fire. Cast iron pans' effectiveness will be destroyed by cleaning them in the dishwasher.
Cast Iron Seasoning
Cast iron pans need to be seasoned when they are new. The finish is not abraded and does not have a nonstick coating. Food will stick without seasoning. Once well-seasoned, food slides right out of the pan and cleaning it is simple. Seasoning requires oil to be rubbed into the pan. Then you cook the pan in the oven at a low heat for an hour. After you let it cool you can wipe any excess oil out and the pan is ready to use. Seasoning is the reason you never put your cast iron pan in the dishwasher.
Cast Iron Care
Cast iron pans should never be washed with soap or detergents. These will break down the oils that you carefully cooked into the iron. Cast iron seasoning gets better with time and frequency of use. In order to preserve the hard-won treatment, you simply need to wipe out the pan. A paper towel will do just fine. Chunks of food and excess oils and juices are easily removed in this way. Really baked-on food can be soaked away in warm water briefly as long as the pan is thoroughly dried.
The Dishwasher Results
Once you put a cast iron pan in the dishwasher your seasoning is gone. The combination of the scrubbing action, warm water and detergent effectively remove the seasoning in the pan. The dishwasher will also rust the iron as it is in a raw unprocessed state. It is unnecessary to use the dishwasher since the wipe method is so efficient. The dishwasher will not remove the blackening on the outside of a cast iron pan. Pans with extreme blackening on the outside can be cleaned manually with good old elbow grease.
If you have put the pan in the dishwasher, you need to start all over reseasoning the pan. Unfortunately, if it is a family heirloom it will never regain that level of seasoning and some associated flavor that goes along with really well-used cast iron. The pitting and scarring in a used pan will result in un-even seasoning that only time can cure. The rust will have gotten into those same pits and scars and will have to be sanded out before treating the pan with oil. It is a lengthy process that will still not give you your old pan back.