The modern kitchen looks much different from the kitchens of the middle ages, and certainly much different from the kitchens of Chazal. Not only have our cooking and cleaning practices changed, e.g., most of us don't use basins heated over the fire to wash dishes, but so have our utensils. While the refrigerator and freezer do not pose major halakhic challenges, microwaves and dishwashers do.
May one use a dishwasher for both meat and dairy dishes? I would like to limit our discussion to consecutive, and not simultaneous, use of the dishwasher. While according to some, there may be room to be lenient even when both meat and dairy dishes are washed together, the halakhic risks - including the biblical prohibition of bishul basar be-chalav - may be greater.
In order to apply the halakhic principles we have discussed, we must describe the cleaning process of a dishwasher.
A dishwasher cleans dishes by spraying water throughout the machine, removing any food residue that was left on the dishes. The water then accumulates at the bottom of the machine. After the rinse, the dishwashing detergent, which is placed in a special receptacle, is released and mixes with hot water, which circulates throughout the machine. The hot, soapy water breaks down the food residue, which is then pumped out of the machine. Pieces of food too large to be pumped out are caught by a filter, located at the bottom of the machine.
For a more detailed explanation of how a dishwasher operates, the following web pages, http://www.repairclinic.com/0088_9_3.asp and http://www.cleaning101.com/dishwash/understanding_automatic_dishwashing.html, may be helpful.
Using Dishwashers for Both Meat and Dairy Consecutively:
The Status of the Dishwasher's Walls:
What is the status of the dishwasher's walls?
Let us say that one washes dairy or meat dishes in a dishwasher. We must ask whether the walls of the dishwasher absorb the taste, rendering the entire dishwasher a milkhig or fleishig utensil. Similarly, we must determine whether the walls of the dishwasher have the ability to impart taste to the dishes being washed.
Regarding the walls of the dishwasher, seemingly, there are two ways in which they can absorb ta'am.
If the concern is ta'am that came from the dishes themselves, certainly that ta'am should be considered "nat bar nat." Incidentally, this rationale applies only to kosher meat or dairy dishes; the taste emitted from non-kosher utensils always has the ability to affect another keli.
If the concern is that taste from meat or dairy food residue may be absorbed into the utensils, then we must ask ourselves: Is the dishwasher an environment in which ta'am can be transferred?
Seemingly, there should be a major difference between dishwashers in America and in Europe/Israel. An American dishwasher receives its water from a separate hot water pipe. The water entering the dishwasher was heated up in the house boiler, rendering the dishwasher a "keli sheni" and not a "keli rishon." Dishwashers in Europe and Israel, however, contain a heating element in the bottom of the machine, rendering the dishwasher a keli rishon.
This difference may be very significant to our discussion. In a future shiur, we will discuss the difference between a keli rishon and keli sheni. It is sufficient to say that if the food particles are heated in a keli sheni, one may argue that the dishwasher bottom never has the potential to absorb ta'am (Shulchan Arukh YD 105:2). Furthermore, the water sprayed by the revolving wand MAY be considered iruy from a keli sheni, which is most likely halakhically insignificant.
If, however, we view the dishwasher as a keli rishon, the food residue is actually cooking in the bottom of the dishwater, and ta'am is absorbed into its walls. If so, then the next time this dishwasher is used, it is equivalent to cooking meat in a dairy pot, which renders the entire machine and its contents basar be-chalav!
Rav Moshe Feinstein (YD 3:11), who argued FOR the permissibility of using one dishwasher for consecutive use of meat and dairy dishes, notes that a dishwasher is a keli sheni, and therefore there may be no halakhic problem. Some argue (see article by Rav Yisrael Rosen, Techumin 11) that dishwashers in Europe and Israel are considered a keli rishon, rendering the heter of Rav Moshe Feinstein not applicable in Israel and Europe.
Incidentally, I am under the impression that newer dishwasher models in America also have built-in heating elements not only for the drying cycle, but also to insure that the water reaches the proper temperature. The web page cited above seems to confirm this. I encourage readers to investigate this point further.
Other Reasons to be Lenient:
Even if we view a dishwasher as an environment which is conducive to a transfer of ta'am - i.e., a keli rishon - consecutive use for milk and dairy dishes may still be permitted. How?
This leniency seems to rely upon the following two factors.
First, we once noted that the Mechaber (95:4) suggests that if one washed DIRTY meat and dairy dishes together in a keli rishon, if one had added ashes or dirt to the water as a cleaning agent, the food residue may be rendered "pagum" (unsuitable) and the dishes may be permitted. Some claim that the highly concentrated detergent used in dishwashers "spoils" any food residue, and therefore there is no problem of "ta'am"!
Others note that both the Shakh and Taz disagree with the ruling of the Mechaber. Furthermore, some argue that large pieces of residue are not spoiled, and remain intact and edible even after the cleaning process.
[This question is the critical point of debate between Rav Gideon Perl (Rav of Alon Shvut) and Rav Yisrael Rosen (Rav of Tzomet), see Techumin v. 11.]
However, it seems that the release of detergent and its effect upon the food residue may not be enough to permit consecutive washing of meat and dairy dishes. The soap is not always released immediately, and therefore there may be free circulation of hot water and remaining food particles before the detergent "spoils" them.
Those who permit the consecutive washing of meat and dairy dishes in a dishwasher often offer another reason to be lenient – bitul be-shishim.
Rav Moshe Feinstein (YD 2:28) and others insist that the food residue is nullified by shishim of water. This assumption is dependent upon the dishwasher, the type of cycle chosen, and the cleanliness of the dishes placed in the dishwasher. Older dishwashers, for example, were less likely to conserve water than newer ones. Additionally, some people are more careful to clean off their plates before placing them into the dishwasher, leaving very little meat or dairy residue. Similarly, if a "pre-wash" cycle is run, the cold water most likely removes most of the residue.
As for the amount of water used in each cycle, each machine seems to use a different amount. My AEG dishwasher, for example, seems to use about 5 liters per rinse (according to the manual). If so, it would follow that the actual meat or dairy residue in our dishwasher must be less than 83.3 milliliters, or, approximately 2.8 ounces which is slightly more than one third of a cup, in order to be considered "batel."
Some have raised a concern that as the water drains, there may not be sixty parts of water left to nullify the remaining food particles. This may be a serious concern. However, if one assumes that the detergent has "spoiled" any remaining food particles, then this concern does not seem relevant.
Filters, Racks and Pareve Dishes:
In most dishwashers, larger food particles remain in the filter and must be manually removed. This raises a number of halakhic problems.
If the filter contains both meat and dairy residue, this may create a situation of bishul basar be-chalav, a Biblical prohibition!
Even if the filter contains ONLY meat or dairy remnants, every time water is heated up in the dishwasher, the water absorbs the taste of the food residue, rendering the water, as well as the dishwasher, milkhig or fleishig.
Seemingly, these problems can be resolved initially by cleaning the filter after each use, or be-di'avad by assuming that the detergent spoils the remnants and/or the water is more than shishim against the food remaining in the filter, which is quite likely.
Another issue, raised by Rav Moshe Feinsten, concerned the use of one set of racks for both the meat and dairy cycles.
Do the racks absorb taste of meat or milk directly from the food? If one views the entire dishwasher as a keli rishon, this may indeed be a problem. If one believes that the water which is sprayed on the racks is considered iruy mi-keli rishon, since in our case the flow of water is interrupted (iruy she-nifsak ha-kiluach), we may not be too concerned. We will discuss the status of iruy in a future shiur. Furthermore, as mentioned above, the ability of ta'am to leave the racks and be absorbed in the dishes may also be questionable.
What if there is meat or dairy residue left on the racks? It seems that in newer dishwashers, the racks are generally clean after a full cycle. The silverware basket, however, often retains small pieces of food residue.
These concerns led Rav Moshe Feinstein (OH 1:104) to insist upon using two separate dish racks.
May one use a meat or dairy dishwasher for pareve dishes? If the filter (and racks) have been cleaned, there seems to be room to sanction this practice (see The Laws of Kashrut by Rav Binyomin Forst, p. 262)
One final question: What if one finds dairy silverware in a meat dishwasher, or vice versa?
Generally speaking, the Rema (95:3) rules that if one finds a dairy spoon among meat cutlery, one is not required to kasher the silverware.
The Acharonim (see Taz 95:13 and others) point out that there are so many sefekot (doubts), one can assume that the dairy spoon was washed in a permissible way. For example, maybe the spoon wasn't actually washed with the meat cutlery. Or, maybe the dishes were clean of residue and at least one of the types was eino ben yomo. Furthermore, maybe the water didn't reach yad soledet bo (often people don't wash dishes in water which is yad soledet bo, as it is very uncomfortable). Additionally, maybe there was shishim of water against the taste, or maybe the soap spoiled any taste that was present. In any case, we have clearly reached the "sefek sefeka" necessary to permit such a case.
Can one make the same assumption regarding a dairy spoon found in a meat dishwasher? Clearly, all the silverware was washed together. Furthermore, the water was clearly hot enough to effect a transfer of taste. While one could possibly make an argument for leniency based upon the presence of shishim, as well as the pungent nature of the detergent, it would seem that in this case one should be stringent and kasher the utensil in question.
We should note that common custom, despite Rav Moshe Feinstein's leniency, is not to use one dishwasher for washing meat and dairy dishes consecutively.
However, those who do permit this practice must accept the following assumptions:
- The detergent spoils the remaining food residue, even when there isn't shishim of water in the machine.
- The food residue, even if at times it is not spoiled, is nullified by shishim of water.
Furthermore, those who use a dishwasher in America, in which the internal heating element does NOT heat the water, may have another reason to be lenient.
For further research, see Igrot Moshe (OH 1:104, YD 2:28 and 29, YD 3:9 and 11, OH 3:55) and Techumim 11 (articles by Rav Gidon Perl and Rav Yisrael Rosen).