Here is a simple tip to keep the inside of your Pressure Cooker (made of aluminum) sparkling white. Pour water in the Pressure Cooker and place the pressure pans with the cooking ingredients. Put 1-2 pieces of lemon, a small ball of tamarind or any other citric ingredient in the water. Pressure-cook the dish the normal way. After cooking, the pan will sparkle white and the usual stains will disappear. For old stubborn stains, you may require to repeat the exercise.