Moed Katan, Chapter Two, Mishnah 2. In the previous Mishnah we dealt with someone who had already begun processing his olives, and then was struck by circumstances beyond his control, or by mourning, or by some other hindrance, and stood to suffer a loss if he did not complete the olive work. Our Mishnah continues with the very same subject, this time with regard to wine.
The case before us:
A person whose wine has already been pressed out of the grapes and is lying in the pit beneath the winepress, and one of the following happened to him:
Mourning: a relative of his died, and now he is a mourner and cannot perform work.
Circumstances beyond his control: or some other hindrance that prevented him from completing the process before Yom Tov.
Workers who misled him: workers who were supposed to do the job before Yom Tov, and did not show up.
In these cases he is permitted to empty out the pit, complete the process, and seal the barrels. These are the words of Rabbi Yosei, consistent with his position that we saw at the end of the previous Mishnah regarding the olives.
The opinion of Rabbi Yehudah:
Rabbi Yehudah, as is his way in the previous Mishnah, limits the scope of the permitted work and allows only what is needed to prevent a major loss. Here too he says that one may make "limudim" - wooden boards. He may not remove the wine from the pit, but he may cover it in a way "shelo yachmitz" - so that it will not turn sour and become vinegar and the wine be lost; but he may not complete the entire process on Chol HaMoed.
In summary: This Mishnah applies to wine the principle taught in the previous Mishnah regarding olives. According to Rabbi Yosei, one who was prevented by circumstances beyond his control and stood to suffer a loss may empty the pit, finish the job, and seal the barrels in the normal manner; whereas according to Rabbi Yehudah, only the act of preventing the loss is permitted, covering with boards so that the wine will not turn sour, but not completing the work.