Kashrut Issues Related to Knives

  • Rav David Brofsky



In previous shiurim, we discussed numerous ways in which taste may be transferred from one substance or utensil to another.  We summarized the scenarios in which ta'am passes between two touching materials, i.e., through the proper medium and in the presence of heat.  We also discussed the impact of reicha and zei'a.


This week I would like to address the transfer of taste, and food residue, through knives.


Contact Between Knives and Cold Food:


Unlike pots and pans, knives present a unique kashrut challenge.  The Gemara (Chullin 111b) states, in the name of Abaye, that if one cuts a cucumber (a mild vegetable) with a meat knife, one should scrape the place where it was cut (gereira), and then one may eat it with milk. 


[This in contrast, of course, to a sharp vegetable (davar charif), such as a radish, cut with a meat knife, which may not be eaten with dairy, as we shall explain in next week's shiur.] 


The Rishonim explain that the Gemara assumes that a knife is particularly difficult to clean properly, and we therefore fear that the blade may contain a thin layer of grease or food residue (shamnunit). 


While merely washing or scrubbing the cucumber should suffice, since a cucumber is soft and wet and cleaning it may actually cause the food residue to be further absorbed, a small piece should be removed before eating it with milk. 


Similarly, the Shulchan Arukh writes (96:5), "One who cut a cucumber with a meat knife may eat [the cucumber] with milk as long as one scrapes off the area of the cut..."


Furthermore, the Shulchan Arukh rules (89:4) that "one may not cut cheese, even if it is cold, with a knife used for cutting meat.  Furthermore, even the bread eaten with cheese may not be cut with a knife used to cut meat."


The Acharonim discuss, at length, when one may simply clean a food and when one must remove the outer layer.  Preferably, if one cuts any food with a dairy knife, it should not be eaten with meat before removing a thin layer. 




Is there a method to clean a knife that would permit cutting cold cheese with a meat knife? Furthermore, be-diavad, are there cases in which food that was cut with a dairy knife MAY be eaten with meat?


Regarding cleaning a knife, the Gemara (Avoda Zara 76b) explains that one may "plunge (no'etz) the knife ten times into the ground."  Tosafot point out that the Yerushalmi mentions plunging the knife into the ground three times, and questions whether the number ten is vital.  In any case, this method, known as "ne'itza," is used to cleanse the knife of any food residue left on the blade.  If, however, the knife is serrated, "ne'itza" is ineffective and libun must be performed. 


The Gemara, explaining the Mishna, is clearly referring to a non-kosher knife which was purchased from a non-Jew.  While the Rishonim debate the proper method of kashering the knife if one intends to use it for hot foods, "neitza" is sufficient for cold foods. 


The Shulchan Arukh (YD 121:7) rules, based on this Gemara, that one who acquires a knife from a non-Jew with the intent to use the knife for cold foods should plunge the knife into the hard ground ten times.  This most likely explains the widespread phenomenon of leaving knives in gardens and flowerpots.  While not halakhically precise, this practice is based upon the above principle. 


Incidentally, as ne'itza is merely a method of cleaning the knife, one might suggest cleaning the knife with another abrasive substance, such as steel wool.  However, this MAY depend on how seriously one is to take the Gemara's insistence on ne'itza TEN times, as we noted above. 


Ne'itza is sufficient only when using a knife for COLD food.  Furthermore, ne'itza is sufficient if one cuts hard cheese with a meat knife, but if the knife wasn't kosher, then ne'itza should only be used as a TEMPORARY solution.  The custom is to kasher all non-kosher utensils intended for permanent use, even if they are only used for cold foods (see Rema YD 121:7). 


Until now we presented ne'itza as a temporary solution when purchasing non-kosher knives. The poskim, however, mention other, more common, cases in which one may be required to do ne'itza.


For example, if one cuts cold meat with a dairy knife and forgets to clean off the residue, the Rema (69:20) seems to rule that dried residue should be removed through ne'itza.  Similarly, the Shakh (94:31) rules that if a meat knife was used to cut a cold HARD dairy substance, or if a dairy knife was used to cut cold HARD meat, ne'itza should be performed.  Finally, the Rema (94:7) requires ne'itza if one cuts WARM meat (i.e., meat which does not cause a transfer of taste from the meat into the knife) with a dairy knife. 


In addition to the above examples of "kitchen accidents," may one use ne'itza, as a regular practice, on one's household kitchen knives, in order to use a meat knife for cheese, or vice versa?


The Rema (YD 89:4) writes that the custom is to keep two knives, one for meat and one for milk, and to label one of them (the minhag, he writes, is to label the dairy knife), and one should not desist from this custom. 


The Acharonim, however, debate whether this custom prohibits all "le-khat'chila" use of ne'itza  (i.e, except when kashering a non-kosher knife).  The Shakh (89:22) maintains that in extenuating circumstances ("she'at hadchak") one may rely upon the original halakha; in other cases one should not use ne'itza. On the other hand, the Taz (89:7) writes that while one should not use a meat knife for cutting cheese, ne'itza may be employed in order to cut bread that will be eaten with cheese.


Some suggest keeping a pareve bread knife, insuring that all bread remains pareve. 


The Status of Salads Cut With Dairy Knives:


As mentioned above, one should not use a dairy knife to cut foods to be eaten with meat.  However, be-diavad, are there cases in which food cut with a dairy knife MAY be eaten with meat? For example, what if one used a dairy knife to cut salad?  May one eat the salad with meat?


As we mentioned above, the Gemara, and subsequently the Shulchan Arukh (YD 96:5), rules that a cucumber or any other bland food which was cut with a meat knife should not be eaten with milk until it is scraped clean (gereira).


However, it would seem that regarding an entire salad, there are a number of reasons to be lenient, be-di'avad.


Firstly, as our knives are usually washed well with dish detergent, one may assume, ex post facto, that any meat residue was already removed, or was at least rendered inedible, i.e., "nifgam."  Secondly, the amount of meat residue that may have been wiped onto the food is certainly "batel" – nullified - throughout the salad, rendering the salad pareve. 


Regarding salads from a salad bar or restaurant, there may be additional reasons to be lenient.  In addition to the above, the knife may have already been cleaned while cutting other fruits and vegetables.  Furthermore, often a salad bar or restaurant uses special utensils for salads, and the knife MAY (depending on the establishment) have the status of a "keli meyuchad," i.e., a knife that we may assume was used ONLY for salads.


However, they may be other reasons to refrain from eating salads prepared without supervision, such as bugs, davar charif (i.e., sharp foods), terumot and ma'aserot (in Israel), non-kosher salad dressings, and possibly even mar'it ayin.  I am only addressing the status of the salad itself. 


Finally, one need not wait after eating a food cut with a meat knife, and may immediately consume dairy products.  We will address the topic of "waiting after meat" in a few weeks. 


Contact Between Knives and Hot Food:


The Tur (YD 94) cites Rabeinu Peretz who maintains that if one cuts a hot piece of meat (in a keli rishon) with a ben yomo dairy knife, one must merely remove a "kelipa" of the meat and the rest is permitted. 


The Tur disagrees, and opines that we may permit the meat only if there is "shishim" against the knife.  In other words, he views this case as analogous to dipping a ben yomo dairy spoon into a pot of meat, in which case the meat is only permitted if there is "shishim" against the spoon.  Furthermore, he writes, that even when we permit the meat, the area that came in contact with the knife must be removed, as we fear that dairy residue (see above) may have been wiped onto the meat.  The knife must be kashered through hag'ala.  If the knife was eino ben yomo, then only a kelipa must be removed and the meat is permitted.  Once again, however, the knife must undergo hag'ala.


The Shulchan Arukh codifies the Turs ruling.  In addition, the Rema is lenient if the meat was already moved to a keli sheni, in which case only a kelipa need be removed.  As we noted in previous shiurim, some Acharonim disagree, viewing the meat as a "davar gush" which maintains its status as a keli rishon as long as it is still "yad soledet bo."


As our discussion of knives is incomplete without properly addressing the topic of "davar charif," next week we will discuss the uniqueness of sharp foods and their impact on various kashrut questions.