As we have learned, meal offerings are usually mixtures that include flour, oil and frankincense. What if these ingredients were mixed outside of the Temple courtyard? Would they become invalid or is the mixing stage not yet part of the formal process of preparing the minḥa?
Rabbi Yoḥanan rules that such a meal offering is invalid; Reish Lakish says that there is no problem with it.
Reish Lakish explains his position by pointing to the passage in Sefer Vayikra (2:2) that teaches that the oil and frankincense are added to the flour and that only afterwards does the kohen take the fistful of the mixture that is to be sacrificed on the altar. He concludes that since there is no need for the kohen to be involved in the original mixing of the ingredients, it is clear that it does not need to be done within the precincts of the Temple. Rabbi Yoḥanan argues that since the meal offering mixture is prepared in a keli sharet – a unique Temple vessel – it is clear that it needs to be made in the Temple, even if it does not need to be prepared by a kohen.
Tosafot point out that according to the continuation of the Gemara (on daf 18a) in the event that the ingredients of the meal offering are placed in the keli sharet but are not mixed at all, nevertheless the minḥa is valid. If so, we have to explain that Rabbi Yoḥanan believes that if the mixing is done in an improper manner it is worse than not being done at all.
On the other hand, Reish Lakish’s argument that the fact that a kohen does not need to be involved in preparing the minḥa indicates that it need not be done in the Temple, seems to be contradicted by the fact that in an ordinary animal sacrifice, sheḥita – slaughtering the animal – can be done by anyone, yet it must be done in the Temple courtyard. The Ḥazon Ish explains that there is a basic difference between sheḥita and mixing the minḥa. While sheḥita is one of the basic Temple services essential to every animal sacrifice, mixing the ingredients for the minḥa does not have that level of importance, so it would only be considered significant if it was part of the priestly service.