A commonly asked question relates to an onion cut with a Fleishig knife and then placed in the food processor. Does it render the appliance Fleishig itself that one could no longer chop an onion in it to place in a Milchig recipe?
According to Halacha, it is assumed that even a perfectly clean utensil will absorb flavor when making contact with hot food. When it is later used with a different hot food, it will impart some of this flavor to the second item. If one was Milchig and the second Fleishig, or the reverse, the result will not be Kosher.
The Gemara relates, and it is codified in Shulchan Aruch Yoreh Deah Siman 96, that a spicy food shares many of the same traits as a physically hot one. In fact, in some ways it is even more serious; as we assume that sharp foods prevent the flavor from degrading when passing though multiple conduits or when more than 24 hours have passed, which is not the case with heat.
Therefore, generally speaking we consider an onion sliced with a Fleishig knife to have become Fleishig itself. Furthermore, even if the knife had not been utilized for hot meat for more than 24 hours before cutting the onion, we will nevertheless deem the onion Fleishig.
The Magen Avraham Orach Chaim 451§31 extends this prohibition and writes that if one would cut ginger with a Fleishig knife and grind it in a mortar, it would be improper to subsequently grind other spices in this same mortar with the intent to add them to a dairy dish. This is roughly analogous to our question regarding the food processor, and is cited in both the Chaye Adam and the Mishna Berura as the accepted Halacha.
However, despite the prominent authorities who endorse and adhere to this stringent ruling, there are also numerous Poskim who dissent.
The Even HaOzer objects to the Magen Avraham’s equating the acknowledged ability of a sharp food to extract a full favor with his assumption that it can impart one as well. He suggests that while an onion or ginger would draw out a rich flavor from the knife and render them Fleishig, it could not insert this into the mortar. Rather, the meaty flavor entering the grinder or food processor would merely be Nat bar Nat, and would not render future items forbidden with milk.
Additionally, the Chavos Da’as observes that there is no indication that a sharp food can overcome the principle that a flavor absorbed in a food cannot be drawn out without liquid. Accordingly, he rules that the meaty flavor contained in the onion or ginger would not enter the mortar at all.
Though the Pri Megadim in Orach Chaim resolves this issue by suggesting that when the spice is ground into a powder in the mortar the flavor contained in it is no longer termed “absorbed”, as reducing it releases the meaty taste, this interpretation will logically lead to a limitation in the Magen Avraham’s stringency. According to his proposal, there would be no grounds for stringency when the onion was merely grated in the food processor. Only when the lower puree blade was used will the absorbed flavor be released without a liquid medium; however, on the higher slicing/grating blade the Magen Avraham would concede that the flavor is not released.
While a large number of Poskim follow these lenient positions, their numbers, in and of itself, would likely be insufficient to overcome the prominence of the stringent ones.
However, there are a number of other factors that can be considered, which will ultimately lead us to the conclusion that this situation can be permitted.
Firstly, the majority of the Poskim consider this trait of spicy foods to be of Rabbinic origin. While the Beis Yosef and other deduce from the Rashba that he considers it to be d’Oraisa, the Pri Megadim observes that he clearly only considered this relevant to Chiltis, asafetida, and not any of the more common sharp foods. Furthermore, the Rashba was specifically addressing the ability of spicy foods to rectify old flavors; there is no indication if their ability to draw out a full flavor is included. While this is not grounds to permit it in and of itself, it does allow us to exhibit a degree of leniency when significant doubt exists.
Secondly, there are a number of authorities who restrict the effects of “sharp foods” to radishes alone (and in the Aruch HaShulchan’s view, only black ones at that). In their opinion, an onion is not capable of extracting flavor from a knife, never mind imparting it to a food processor.
Thirdly, there are significant Poskim who assume that only Chiltis is capable of rejuvenating yesterday’s absorptions, and not onions or even radishes.
While both of the previous two opinions are in contradiction to the accepted ruling of the Shulchan Aruch, it is obvious that the Shach and other Poskim do take them into consideration in conjunction with additional factors.
Consequently, when either the knife utilized to cut the onion or the food processor were not used for 24 hours prior to the questionable process, there should be no problem placing this onion subsequently into a dairy dish, and the onion could even be pureed in the food processor with this intent. If both were recently used, only the grating blade should be used and not the puree one. However, one should refrain from knowingly cutting an onion with a Fleishig knife with the intent to place it in a food processor maintained as Pareve, as this would potentially be an issue of wantonly creating Nat bar Nat.