Shabbat Parashat Toldot 5772

Ask the Rabbi: Does a Cutting Board for Onions Take on the Status of the Knife Used?

Question:  I cut an onion on a pareve plastic cutting board with a fleishig knife. Does it make the cutting board fleishig like the onion?

Answer:  Had you cut a potato with a fleishig knife, it would not have become fleishig for up to three reasons: Taste transfer from a utensil to a food requires heat; the taste expelled from a fleishig utensil into a pareve food (nat bar nat) is too weak to be a building block of a prohibited milk/meat combination; taste remaining in the walls of a kli for 24 hours is assumed to give a negative taste (notein ta’am lifgam) to the food it enters and not change its halachic status.

Poskim derive from two gemarot that these leniencies do not apply to a davar charif (a sharp food), including, according to most, onions. Avoda Zara 39a says that one may not eat chiltit (a very sharp food) bought from a non-Jew because they cut it with non-kosher knives. The gemara posits that there is a transfer without heat from a non-kosher knife to this davar charif and that it is prohibited even if the knife had not been used within 24 hours. Chulin 111b says that a radish cut with a fleishig knife may not be eaten with milchig food. Besides the matter of cold transfer, we learn that a “twice-removed” fleishig taste in a davar charif is forbidden with a milichig food.

However, the rules in these gemarot may be limited. Some say that only the ultra sharp chiltit removes the leniency of notein ta’am lifgam (see Beit Yosef, Yoreh Deah 96). Also, some say that the problem with the radish cut with a fleishig knife is that most knives have caked on fat on their blade (see Rashi, Chulin 1121a and Aruch Hashulchan, Yoreh Deah 96:15), and maybe today we keep knives cleaner (see Badei Hashulchan 96:10). However, the Rama (Yoreh Deah 96:1) is stringent on all grounds, Therefore, you are correct that the onion is fleishig.

Your case has two additional points of leniency. One is that the gemarot discuss the davar charif as absorbing the taste in question. The sharpness may heighten the taste’s absorption and/or how people sense it. Here, though, the question is not just about the onion’s ability to become fleishig but whether it is uniquely capable of making other things fleishig. The Magen Avraham (451:31) does say that if ginger was cut with a fleishig knife and then it was ground, the mortar and the spices later ground in it becomes fleishig.  However, the Even Haozer argues that fleishig taste that leaves a davar charif loses its special qualities, and therefore the mortar remains pareve.  

Another factor is that the gemara says that transfer of taste without heat occurs only due to the combination of “the knife’s pressure” and the davar charif. Is a cutting board subject to this special pressure that the gemara discussed? The cutting board would not seem to be affected by the friction of cutting. There are differing opinions (see Badei Hashulchan 96:7) on this matter on whether the downward pressure on the cutting board is equivalent. (The Shulchan Aruch, Yoreh Deah 96:3 compares crushing with a mortar and pestle as equivalent, but there the pressure seems to be much stronger.)

Considering all the reasons for leniency, it is hard to say that hard, smooth surfaces like glass or glazed material would become fleishig due to the cutting that occurs on top of them. On the other hand, regarding the type of plastic cutting board that is rough and has multiple deep serrations from repeated use, taste from the onion can accumulate and be difficult to remove. One can also speak, in that case, about a certain amount of friction during cutting. There, one should at least scrub the surface well before non-fleishig use, and, while we not require it, kashering it would but an understandable stringency.

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