With these principles in mind, what can we kasher in the kitchen? Plastic and nylon materials are the subjects of halachic debate. According to Rav Moshe Feinstein, synthetic materials made of chemical mixtures such as plastic and nylon cannot be kashered for Pesach. According to other opinions, plastic or nylon vessels may be kashered. This can be done either by the process of hagalah or, if this will damage the vessel, by the dual process of immersing it in hot water that has been removed from the fire and then by the procedure of milui veirui. According to Rav Moshe, Pyrex, Duralex and Corningware cannot be kashered. Others permit the kashering of Pyrex and other heat-resistant glass utensils by the process of hagalah if used for hot food and by the process of milui veirui if used for cold food. According to Rav Moshe, dishwashers lined with plastic walls cannot be kashered.
According to other opinions, a plastic-lined dishwasher can be kashered in the following way: First, it must be thoroughly scrubbed. Then it should not be used for twenty-four hours. Then the dishwasher should be turned on to allow boiling water to spray inside. Dishwashers lined with porcelain or enamel cannot be kashered. Gas or electric ovens can be kashered by libun and according to some poskim even by libun kal. According to Rav Moshe, such ovens can be kashered by running them through the self-cleaning cycle.
Microwave ovens can be kashered. They should be thoroughly cleaned and not used for twenty-four hours. Then a bowl of water should be placed inside. The microwave oven should then be turned on until the inside is filled with steam.
Mixers used for mixing dough or other chametz can generally not be kashered because it is almost impossible to remove the chametz particles trapped in the machine. Blenders that can be dismantled should be thoroughly cleaned and their metal parts and bowls immersed in boiling water. Coffee percolators, to the extent that they can be thoroughly cleaned of all chametz particles, can be kashered by boiling water inside them. Rabbi Shimon Eider, however, writes that they should not be kashered because it is impossible to clean out all chametz particles.
According to most opinions, whisky glasses cannot be kashered because they retain the smell and flavor of whisky. The Aruch Hashulchan (Orach Chaim 451:49), however, rules that they can be kashered by milui and irui.
Because there are so many conflicting opinions in this area of halacha, in case of doubt a rabbi should be consulted.
