Microwaves and dishwasher are usually made of synthetic materials, such as plastic. There are differing opinions as to whether one may kasher such materials. Some poskim have held that since we have no mesorah (clear tradition) on these new materials, we must be strict and not allow kashering. Others have argued that the Torah specifically singles out cheres (earthenware) as the one material that cannot be kashered, because it can never be completely purged. We should therefore assume that any other material can be kashered, unless it is proven that it too cannot be completely purged.
Rav Moshe Feinstein zt”l writes that because there is an uncertainty as to whether plastic can be kashered, one may be lenient as per the dictum safek d’rabbananl’kula, provided the utensil was not used for 24 hours. It is questionable,
though, as to whether Rav Moshe Feinstein intended this leniency for Passover as well . Everyone is encouraged to ask their own Rabbi for guidance.
Microwave ovens also contain glass windows. Although the Shulchan Aruch holds that glass does not absorb and
therefore does not need to be kashered for Passover, Ashkenazi Jews follow the opinion of Rema that glass is compared to cheres and may not be kashered.
Another important consideration is, how does one perform hagalahon a microwave? Clearly, one cannot submerge a microwave into a pot of boiling water. Many poskim hold that we follow the rule k’bolo kach polto (the way a utensil can be kashered is directly related to the way it absorbs) to allow a utensil which only absorbed through contact with ze’iya (steam) to be kashered with ze’iya. Since the primary concern for absorption in the walls of the microwave is through steam, the way to kasher is by applying steam. This steaming should be done for a longer duration than it would be used during the year. The entire microwave must be thoroughly cleaned. Plastic surface cleansers should be used to make sure that all six sides of the microwave are clean. A toothpick should be used to clean out the holes of the vent. If any particles splattered through the vent, they are likely too far away from the zeiya to pose an issue.
MICROWAVE KASHERING INSTRUCTIONS
Therefore, someone who wishes to use a year-round microwave on Passover should do the following.
•The microwave should be cleaned out very well.
•Liquid cleanser should be sprayed on all surfaces and washed off.
•The turntable should be removed and replaced with new Kosher for Passover surface.
•The microwave should be left idle for 24 hours.
•A clean drinking glass, unused for 24 hours, should be filled with water and boiled in the microwave for 10 minutes (Note: it might take several minutes for the water to begin to boil).
•The cup should be refilled and moved to another spot and the process repeated for 10 more minutes.
•A piece of cardboard or contact paper should be taped over the glass window pane.
•(If one does not kasher plastic for Passover, then all of the surfaces should be covered with cardboard or contact paper. Make sure to leave holes for the vents.)
Dishwashers are often made from plastic and are subject to theabove discussion. However, if they are made from porcelain they cannot be kashered, while if they are made from stainless steel then they can be kashered. However, one should note that stainless steel dishwashers also contain synthetic components such as rubber gaskets and rubber tubing.
During a cycle, water is pumped down the drain pipe and back up through the spinners into the dishwashing chamber. These tubes need to be kashered as well. However, narrow pipes that one cannot reach inside and scrub may not be kashered . Some Rabbanim have permitted kashering such utensils if they are flushed through with a hot caustic solution that will render inedible any particles that might have adhered inside the pipes. Another issue in kashering dishwashers is the temperature for kashering. Even dishwashers that have a heating element do not raise the temperature anywhere near boiling (75°C is usually the hottest). Rav Moshe Feinstein writes that although running the dishwasher through a cycle would constitute a bidi’eved kashering (i.e., it might be acceptable if it had
already been done) of k’bolo kach polto (kashering at the same temperature at which the is absorbed), lechatchila (i.e., from the outset), one may only kasher with boiling water (212°F). To facilitate this, a large pot of water can be boiled on the stove and poured in. Rav Moshe Feinstein also recommends that heated stones be placed in the dishwasher to ensure that the water in the dishwasher reaches 212°F. The stones must be placed on a protective surface to make sure the plastic will not melt.
Some individuals (or communities) wish to avoid leniencies, particularly in their Passover observance. Yet for others
having use of their appliances on Passover is a basic essential. It is therefore recommended that these guidelines be discussed with one’s Rabbi to see what method for kashering is appropriate given one’s particular circumstances.
DISHWASHER KASHERING INSTRUCTIONS
Therefore if one wishes to use a non-porcelain year-round dishwasher on Passover, the following should be done:
•If it is made of plastic or has synthetic gaskets, speak to your Rabbi as to whether it can be kashered for Passover.
•Clean all surfaces using liquid cleanser.
•Leave the dishwasher idle for 24 hours.
•Run a heated cycle of the dishwasher with soap.
•Boil large pots of water on stove and pour into the dishwasher
•Add heated stones.
•Run a heated dishwashing cycle.