As it is taught in a baraita (Tosefta, Terumot 2:8): With regard to one who inspects a barrel to see if it still contains enough wine to continually mentally separate teruma from it to exempt other untithed wine he has, until all the wine in that barrel would be teruma and would be given to a priest, and afterward the contents of the barrel were found to have turned to vinegar, which cannot be set aside as teruma for untithed wine, then all three days after he had last inspected it, it is definitely viewed as having been wine, and any wine for which teruma was separated during those days is tithed. From that point onward, more than three days after the previous inspection, it is uncertain as to whether it had already turned to vinegar, and any wine for which teruma was separated during those days is not tithed.

The Gemara clarifies: What is the baraita saying? Rabbi Yoḥanan says that this is what it is saying: For all of the first three days following the inspection, it is definitely viewed as having been wine that had not yet turned to vinegar. From that point onward, it is uncertain as to whether it had already turned to vinegar. Accordingly, any wine for which teruma was separated after those three days by means of designating the contents of that barrel as teruma has an uncertain status.

What is the reason? The process in which wine turns sour and becomes vinegar starts with the wine at the top of the barrel; and it is that wine which he tasted when he inspected it, and at that time it had not yet soured. And even if you say that immediately after he tasted it the wine began to sour, during the following three days it would have the odor of vinegar and its taste would be of wine, and anything that has an odor of vinegar but its taste is of wine is regarded as wine.

And Rabbi Yehoshua ben Levi says that there is a different interpretation of the baraita: For all of the last three days preceding the discovery that the wine had turned into vinegar, it is definitely viewed as having been vinegar. From that point and earlier, until the time it had been inspected, it is uncertain whether or not it was wine or vinegar.

What is the reason? The process in which wine turns sour and becomes vinegar starts with the wine at the bottom of the barrel, and therefore, since the inspection was limited to the wine at the top of the barrel, it is possible to say that wine at the bottom had already started to sour and one was unaware of it. Consequently, it is possible that on the day he tasted it the wine turned entirely into vinegar. And even if you say that the process in which wine turns sour and becomes vinegar starts with the wine at the top of the barrel, and it is that wine that he tasted when he inspected it and at that time it had not yet soured, perhaps immediately after he tasted it the wine began to sour, in which case its odor would be of vinegar and its taste of wine, and anything that has an odor of vinegar but its taste is of wine is regarded as vinegar.

The Sages of the South taught another interpretation of the baraita in the name of Rabbi Yehoshua ben Levi: For the first three days it is definitely viewed as having been wine. For the last three days it is definitely viewed as having been vinegar. The status of the wine during the intervening period is uncertain.

The Gemara asks: This matter itself is difficult, as, since you said that for the first three days it is definitely viewed as having been wine; apparently, if it has the odor of vinegar but its taste is of wine it is regarded as wine. But then you said that for the last three days it is definitely viewed as having been vinegar; apparently, if it has the odor of vinegar but its taste is of wine it is regarded as vinegar, as it can be established only that the odor had changed three days ago.

The Gemara resolves the difficulty: The Sages of the South hold that as long as the wine still tastes like wine, it is regarded as wine. When they said that when a barrel is found to contain vinegar it is certain that the wine had already turned into vinegar three days previously, they were referring to a case where the barrel was found to contain strong vinegar, as, had it not already soured three days previously, the barrel would not have been found to contain strong vinegar; rather, it would contain only mild vinegar.

Rav Yosef claimed that this baraita can serve as proof with regard to which blessing is recited over wine that has the odor of vinegar but tastes like wine. Having cited three different interpretations of the baraita, the Gemara asks: In accordance with whose interpretation did Rav Yosef resolve the question of which blessing to recite? Rav Mari and Rav Zevid disagree about it. One said that Rav Yosef resolved it in accordance with the interpretation of Rabbi Yoḥanan, that this liquid is regarded as wine and the blessing for wine should be recited over it. And one said that Rav Yosef resolved it in accordance with the interpretation of Rabbi Yehoshua ben Levi, that the liquid is regarded as vinegar and the generic blessing: By Whose word all things came to be, should be recited over it. There is no definitive resolution of the dispute.

§ An amoraic dispute was stated with regard to one who sells a barrel of wine to another, and following the sale it turned to vinegar. Rav said: If it soured during any of the first three days following the sale, it is presumed that it had already began to sour in the domain of the seller, and he bears financial responsibility for it; from that point onward, it is presumed that the wine soured in the domain of the buyer, and it is his loss.