Eruvin 99B

וכן בגת.

And the same applies in a winepress. This winepress cannot be a private domain, as the first clause of the Mishnah already dealt with a private domain. The winepress must therefore be a karmelit, which proves that it is prohibited to drink from a karmelit while standing in a public domain.

ורבא אמר: לענין מעשר. וכן אמר רב ששת: ״וכן בגת״⁠ — לענין מעשר.

And Rava said: This proof is not conclusive, as the words: The same applies in a winepress, do not refer to Shabbat but to the matter of the halakhot of tithes, as explained below. And similarly, Rav Sheshet said that the statement that the same applies in a winepress refers to the matter of tithes.

דתנן: שותין על הגת, בין בחמין ובין בצונן, ופטור ⁠— דברי רבי מאיר. רבי אליעזר בר צדוק מחייב.

The Talmud clarifies this statement. As we learned in a Mishnah: One may drink grape juice directly on the winepress ab initio without tithing, whether the juice was diluted with hot water, even though he will then be unable to return the leftover wine to the press, as it would ruin all the wine in the press, or whether the juice was diluted with cold water, in which case he could return the leftover wine without ruining the rest, and he is exempt. Drinking that way is considered incidental drinking, and anything that is not a fixed meal is exempt from tithing. This is the statement of R' Meir. R' Eliezer bar Tzadok deems one obligated to tithe in both cases.

וחכמים אומרים: על החמין חייב, ועל הצונן פטור. מפני שמחזיר את המותר.

And the Rabbis say: There is a distinction between these two cases. When the juice is diluted with hot water, since one cannot return what is left of the juice to the press, he is obligated to tithe it, as this drinking is like fixed drinking for which one is obligated to tithe. However, when the juice is diluted with cold water, he is exempt from tithing it, because he can return the leftover juice to the press. Therefore, it is considered incidental drinking, which is exempt from tithing. The teaching of the Mishnah: The same applies to a winepress, is in accordance with the opinion of R' Meir, as it teaches that that the leniency to drink without separating tithes applies only if the drinker’s head and most of his body are in the winepress.