Commentaire sur Démaï 6:7

אחד מעשר – one who can be relied on in matters of tithes and Terumah on the tithes.

Introduction This mishnah deals with a case where two people gathered their grapes into one winepress. One of them tithes and the other does not. The question is: how much of the wine does the one who tithes have to tithe, all of the wine, or only the share that he ends up taking?

ואחד אינו מעשר – cannot be relied upon regarding the tithes.

Two gathered [the fruit of] their vineyards into one winepress, one of whom tithes and the other does not tithe the one who tithes may tithe his own share and his share wherever it may be. The one who tithes must separate tithes both for the share of the wine that he actually takes for himself, and for his “actual” share, wherever that may end up. In other words, if the wine that comes from his grapes ends up in the other person’s hands, and the other person doesn’t tithe, it will turn out that it is as if he sold the other person untithed produce. Above in mishnah 2:2 we learned that one must tithe the produce that one sells to someone who is known not to tithe.

המעשר מעשר את שלו – he makes things legally fit for use by giving the priestly dues on the half of all of what was grown in the vineyard belonging to both of them.

וחלקו בכל מקום שהוא – In the Jerusalem Talmud it explains that this is what he said: and the portion of his colleague, that is, of that which he did not tithe in every place is doubtfully tithed produce. And because there is no choice, we suspect lest half of the part of the person who tithes is in the hand of his colleague who does not tithe and half of the portion of his colleague is in his hand, therefore, even though he already made things legally fit by giving priestly dues of the half of all things that he grew in the vineyard, he is obligated to make things legally fit by giving priestly dues according to the law of doubtfully tithed produce for half of the portion of his colleague that is in his hand.