Jews who keep kosher observe various religious laws, such as not mixing meat or poultry with dairy products, and not consuming products made from pigs or other non-kosher animals. The laws of kosher don't just relate to the food itself, however. Jews who keeps kosher will also make sure not to use any cooking utensils or appliances -- such as a grill -- that were used to cook non-kosher food. If they want to use a grill that was used to cook non-kosher food, they need to "kosher" it, or make it kosher. It must be heated until it glows, in a process known as "libbun gamur."
Remove the grates and set them on top of a layer of charcoal briquettes. Put a second layer of charcoal on top of the grates, and light the charcoal. This should heat the grates until they glow, which constitutes libbun gamur. Alternatively, have a professional heat the grates using a blowtorch.
Blowtorch the part of the grill cavity that is level with and above the grates. This area of the grill may have directly touched non-kosher food, and needs libbun gamur.
Clean the grill cavity well, using steel wool and oven cleaner as necessary to get off all "mamshus," or tangible materials left from the cooked food.
Close the bonnet of the grill.
Turn the grill to its highest setting, usually "broil", and leave it on for 40 minutes. This koshers the inner cavity of the grill through a method called "libbun kal."
Instead of blowtorching the grill's grates, you can just replace them. New grill grates do not require koshering.
Only someone who is experienced should use a blowtorch.