Kashering Electrical Appliances - Part 2 (Microwave Ovens and Dishwashers)

  • Harav Baruch Gigi

Translated and adapted by Rav Eliezer Kwass

To read part one of this shiur click here. 




            For a discussion of how microwave ovens work and the differences between them and normal electric ovens, see Professor Zev Lev's article in Techumin volume 8.  In this context we will summarize his suggestion for kashering microwave ovens.  We will follow with an alternate suggestion offered by the Tzomet Institute in their introduction to that volume.


Professor Lev:


            The whole inside surface of the oven, including its walls and door, should be cleaned thoroughly of even the slightest remnants of chametz.  The oven should be left unused for twenty-four hours.  Afterwards water (preferably mixed with detergent or some other inedible material) should be boiled inside the oven until the walls reach their maximum heat.  The oven is then ready for Pesach use.  The main reason for the boiling is to remove any chametz that got absorbed into the walls of the oven.


            One should take care to cook things in the microwave with a cover; this reduces the chance of them absorbing any chametz that may be expelled by the walls of the oven.  During the rest of the year covering everything used in the microwave enables it to be used for both meat and milk dishes.  (In my opinion both meat and milk dishes should be covered.)


            The glass plate that food is placed on can be treated like glass vessels and be kashered through "hag'ala" done by soaking in water for seventy-two hours with a change of water every day.  For those who are stringent and do not kasher Pyrex, the tray should be switched for Pesach (Sefaradim can certainly kasher it through "hag'ala", and perhaps Ashkenazim can as well.)




            A microwave can be used on Pesach if the food being cooked is placed in a container within another container.  The closed food container should be placed within a larger container (a large refrigerator storage container, or even a cardboard box that fits the dimensions of the oven).  Before using the oven on Pesach, the microwave should be cleaned well and not used for twenty-four hours.


            The box should not be open to the inside of the oven.




            Much has been written on kashering dishwashers for Pesach and using them for both meat and milk (see Techumin volume 11).  The following is what appears to me the most sensible suggestion.


Using For Meat and Milk


            In order to wash meat and milk utensils one after the other: One should wash off the utensils from significantly sized remnants of food (it is preferable that all visible food be washed off).  Different trays should be used for meat and milk.  Since the trays usually have direct contact with the food on the utensils, using the same trays might require complete "hag'ala" between meat and milk.  Likewise, the strainers at the bottom of the machine should be cleaned well between meat and milk washings.   


            This lenient approach is well-based (see the source material brought in Techumin 11):

1. In general there is not so much actual food left on the utensils, and it is most likely negated one in sixty ("batel be-shishim").

2. Furthermore, the detergents used in the wash mar the taste of the food, transforming it into "ta'am li-fgam" (taste that has been rendered inedible). 

3. One can also assume that the walls of the dishwasher do not absorb food directly, but only through the medium of the water (known in halakha as the "ta'am," the "taste" of the food - this is usually contrasted with "be-ein," the food itself).  Only a pale remnant of meat ("ta'am") that has been absorbed in the walls of the dishwasher mixes with the milk that has been similarly absorbed.  This is a mixture of only "notein ta'am bar notein ta'am de-heteira," meaning that not even the "ta'amim" of the meat and milk mix directly ["Taam" of meat gets absorbed in the walls of the dishwasher, then, when expelled from the walls] during the washing, it mixes with "ta'am" of milk.  "Basar be-chalav", the prohibited mixture of meat and milk, cannot come into existence from such a weak mixture.


            I find it hard to permit washing milk and meat vessels together, though.  Similarly, it seems that one needs separate trays for meat and for milk.  Some require that the dishwasher be run empty between meat and milk in order to perform "hag'ala," to remove the meat or milk from the walls of the dishwasher.  As I have said, I do not think that is necessary, and it seems that that is not common practice.


Kashering for Pesach:


            The trays, strainers, and any other removable pieces should be kashered through normal "hag'ala" in boiling water in a "keli rishon" (vessel with water cooked directly on the fire).  [Large trays can be kashered in the large kashering pots set up all over Israel before Pesach.]

            The walls of the dishwasher also require "hag'ala" to remove the chametz absorbed in them.  Rav Moshe Feinstein z"l (Igrot Moshe YD 3:58) rules that the dishwasher should be kashered in a way that the water inside of it reaches a temperature slightly higher than that of the water that is normally used in it.  The dishwasher should not be used for twenty-four hours, then it should be put on its highest setting and run, preferably with detergent inside.  He suggests that ideally ("me-'ikar ha-din") hot iron should be placed in the water to make it boil (the water in a dishwasher usually only reaches 60-65 degrees Celsius, 140-149 degrees Fahrenheit).  This is, of course, very difficult to execute, nor does it ensure that the water will boil.  However, Rav Moshe added that this extra step is only ideal. 

            It seems that the principle being applied is "ke-vol'o kakh polto," removing material in a manner similar to the way in which it was absorbed.  Therefore, the "hag'ala" can really be performed at the highest temperature of the dishwasher.  To make sure that this actually happens it makes sense to heat the water slightly higher than normal.  This could be accomplished by boiling water and throwing it in with the water in the dishwasher.  Then it will definitely reach the highest possible temperature at which anything might have been absorbed.




by Rav Mordechai Friedman



            The following is an editor's comment on the halakhic shiur by Rav Baruch Gigi on "Kashering Electric Appliances."


            Regarding Dishwashers: There are two important points that are not dealt with in the shiur: (when I brought them to Rav Gigi's attention, he agreed.)


1. The presence of a filter, which retains solids until manually cleaned.  Even the most meticulous people may regularly forget to bend down, remove the bottom rack and remove and clean this filter between milk and meat.  The result is not just ta'am being mixed but actual milk and meat solids.  The use of detergent to mar the mere TA'AM (taste) is not universally accepted by all poskim.  In our case, be'en, actual food solids are involved; relying on the detergent to mar the entire food solid is problematic.


2.  The heating element: In many dishwashers there is a cold rinse cycle, which drains immediately, followed by a hot soap wash cycle.  During this cycle the machine fills with cold water which gets heated by a HEATING ELEMENT situated in the collection basin. Rav Moshe Feinstein zt"l in his responsa on dishwashers dealt with dishwashing machines of 20 years ago.  They had a separate hot water inlet with NO element rendering them to be kli sheini.  The well-known siman 95:3 in the Shulchan Arukh Yoreh De'a and the Rama, which allows washing DIRTY meat dishes and (according to the Rama) AFTERWARDS dirty milk dishes, pertains only to a kli sheini. The presence of the heating element changes the halakhic picture entirely.


            This point can be clearly illustrated: A new dishwasher is first used for dirty milk dishes.  The rinse cycle washes most of the particles off, but the filter catches all solids (hard cheese etc.).  The machine refills and starts spraying water while the heating element which is immersed in this mixture of water and cheese particles heats the water to 55-65 degrees Celsius (131-149 degrees Fahrenheit) (45 degrees Celsius, 113 degrees Fahrenheit being yad soledet for bishul).  Assuming (for now) there is not 60 times more water, the catch basin becomes absorbed with ta'am of milk - a milchig kli.  Now, the same machine is used for meat.  We reach a status of cooking pieces of meat in water in a milchig kli.


            The halakha here is that this kli is saturated with basar ve-chalav ('nat bar nat' is NOT an issue here).  Any water boiled from now on in this pot is considered non-kosher (chaticha na'aseh neveila).


            The machine will now spray the dishes with this non-kosher water.  (It is irui kli rishon - which is nivla kedei klipa).


            It is my opinion that, even if a person meticulously cleaned the filter, because of the above-mentioned heating element, the dishwasher would require kashering before every milk-meat switch.  This switch-over is in and of itself problematic according to Ashkenazi minhag.


On the Actual Possibility of Kashering:


Plastic:  Other than extenuating circumstances, the accepted practice is to regard plastics as non-kasherable.  This is due to Rav Moshe Feinstein's psak that we cannot halakhically assume that hag'ala can kasher materials unknown to "our predecessors."  I know of no posek (other than Rav Moshe's disciples) who agrees to this point.  (Please write to me if you know of any.)  There are MANY who allow it.  Those who allow it are:  Seridei Esh II ch. 106; Chelkat Yaakov ch. 163; Tzitz Eliezer IV ch. 6; Chazon Ovadia Hilkhot Hag'ala paragraph 7; Yesodei Yeshurun VI ch. 171.  There are poskim who do not allow it under normal circumstances due to the concern that a person will be afraid to boil them, lest they melt.  I feel that we must differentiate between the vast array of various plastics.  Some absorb tastes and colors that, from my experience, do NOT come out with boiling.


Enamel Coating: is widely accepted to share the category of cheres = porcelain.


            Add to the plastic and enamel question the fact that even those poskim who permit their kashering - when seams or cracks are present, like any pot to be kashered, these pieces must be taken away and cleaned.  The immense amount of seams between the various parts of a dishwasher makes proper kashering a job so difficult, frustrating and time-consuming that it borders on the futile - at least for the 7 days of Pesach.


            Wishing all our readers a chag kasher AND sameach (two wishes not necessarily mutually exclusive!),


                         Mordechai Friedman

                         Halakha Editor