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By Rabbi Dovid Cohen, Administrative Rabbinic Coordinator

Q. We just moved into an apartment with a dishwasher, and the previous tenants were not Shomer Shabbos.  What do we have to do, so we can use the dishwasher?  

A. The first thing to consider is what material the dishwasher is made of.  If the chamber is made of porcelain enamel, then it cannot be kashered (and, of course, that means you can’t use it either), but if it is stainless steel then it can be kashered.  There are different opinions whether plastic can be kashered, and if that’s what your dishwasher’s chamber is made of, you’ll have to ask your local Rabbi for a decision as to whether you can kasher it.  It’s common that that the dishracks and silverware holders are plastic (or at least coated in plastic), which basically means that anyone considering kashering a dishwasher will have to get a Rabbinic ruling on whether they can kasher plastic.

The truth is that there is a second question that must be addressed regarding the dishracks and silverware holders.  These have many cracks and crevices where food can get trapped, and Rema rules that items like that should not be kashered, since it is hard to remove all food residue from them.  Some take that ruling at face value and apply it to dishwashers; therefore, they require that the dishracks and silverware holders be replaced as part of kashering the machine.  Others assume that Rema is only machmir for sieves, or other utensils, where leftover residue might end up in the kosher food.  However, they suggest that he would be lenient for a dishwasher, where the worst-case scenario is that ta’am of that residue might spread to the dishes, but there’s basically no chance an actual piece of non-kosher leftovers will end up in the kosher food.  A third approach says that Rema is only machmir for Pesach – where even a tiny bit of chametz (mashehu) is enough to forbid the food – but for year-round kashering he would be satisfied if the person made sure to clean the utensils very carefully.  This is a question you’ll have to ask your Rabbi, who can give you direction on the matter.

Once you’ve resolved the question of what can be kashered, the actual kashering procedure is not too difficult.  It is based on the principle of k’bol’oh kach polto, which means that (in most cases) kashering needs to mimic the way the utensil became non-kosher.  In the case of a dishwasher, that happens when hot water (mixed with non-kosher food) sprays all around the dishwasher, and kashering will be done in the same manner.  To accomplish that, set the dishwasher on its hottest cycle, and if there is a “food sensor” be sure to turn that off.  [The sensor lowers the temperature when it detects that there is no food residue, which means that during kashering – when the dishwasher is empty – the water will not be hot enough.  Therefore, the sensor should be turned off.]  Run a cleaning cycle with those “hottest cycle” settings, and the dishwasher will be ready for use as kosher.  As with all kashering, the dishwasher must be clean and not used for 24 hours before you start the procedure.

This article first appeared in the Let’s Talk Kashrus column, Yated Ne’eman, February 23, 2024.