Gemara

95b (Rav Yehudah): One blesses Borei Peri ha'Gafen on wine fit to sell in a store.

(Rav Chisda): That is bad wine! One blesses on it sheha'Kol.

Question (Beraisa): One blesses sheha'Kol on wine that became Koses (slimy).

Answer (Rav Zvid): Rav Yehudah admits regarding very bad wine that is sold only at the crossroads.

(Beraisa): If one used to declare that tithes on his wine take effect on wine in a certain barrel, and he checked and found that the wine in the barrel had become vinegar, the first three days are definite. Past this is doubtful.

Opinion #1 (R. Yochanan): The first three days (after it was last checked, and was found to be wine), it was surely wine. After this, it is a Safek.

He holds that wine spoils from the top. Even if it started souring immediately after the last tasting, even if it smelled like vinegar, it would taste like wine for three days. This is still considered wine.

Version #1 - Opinion #2 (R. Yehoshua ben Levi): The last three days (before it was found to be vinegar) it was surely vinegar. Before this, it is a Safek.

He holds that wine spoils from the bottom. (If it tastes like vinegar now, it smelled like vinegar three days ago. He holds that this is vinegar.) Maybe it already spoiled when he last tasted it. Even if wine spoils from the top, perhaps it began to smell like vinegar right after the last tasting; this is considered vinegar.

Version #2 (Chachamim of the south) Opinion #2 (R. Yehoshua ben Levi): The first three days (after he last checked it), it was surely wine. The last three days (before now) it was surely vinegar. The intermediate days are a Safek.

Question: If the first three days it was surely wine, he must say that if it smells like vinegar but tastes like wine, it is wine. However, he says that the last three days it was surely vinegar, i.e. whatever smells like vinegar is vinegar!

Answer: (Really, whatever tastes like wine is wine.) The case is, he found that it is very strong vinegar, so surely it tasted like vinegar three days ago.

97a (Rav): One must make Kidush on wine Kosher for Nesachim (libations poured on the Mizbe'ach).

97b: He excludes wine that is Koses or smells bad.

(Beraisa): These are Pasul for Nesachim even b'Di'eved.

Avodah Zarah 66a: Abaye holds that if wine tastes like wine, but smells like vinegar, it is considered vinegar. Rava holds that it is considered wine.

Rishonim

Rif and Rosh (Pesachim 23a and Bava Basra 6:8): The Halachah follows R. Yochanan, for Rava (in Avodah Zarah) holds like him.

Rosh: Also, according to Chachamim of the south, R. Yehoshua ben Levi agrees with R. Yochanan.

Rambam (Hilchos Berachos 8:8): One blesses sheha'Kol on wine that became Koses.

Rambam (Hilchos Shabbos 29:15): If wine smells like wine and tastes like vinegar, one may not say Kidush on it.

Rambam (17): If wine smells like vinegar and tastes like wine, one may say Kidush on it.

Poskim

Shulchan Aruch (OC 204:.3): One blesses Borei Peri ha'Gefen on wine that smells like vinegar and tastes like wine.

Beis Yosef (DH u'Mah she'Chosav Yayin): The Beraisa mentions wine that was Hikrim. Rashi explains that this is Butir (it formed a crust). The Tur explains that this is only if it smells like wine and tastes like vinegar. If it smells like vinegar and tastes like wine, we hold like Rava (against Abaye), that it is wine. R. Yochanan agrees. Therefore, we bless Borei Peri ha'Gefen.

Bach (1): Birkos Maharam and the Tur explain that wine that was Hikrim is Zeigra; it smells like wine but tastes like vinegar. Why didn't the Beraisa simply say that if it tastes like vinegar, we bless sheha'Kol? Also, why did the Tur need to teach that one may not use it for Kidush? This is obvious, for we bless sheha'Kol on it! It seems that we bless sheha'Kol only when it is evident that it soured. This is why the Beraisa says Hikrim, i.e. it formed a crust (Kanik). If it smells like wine but tastes like vinegar, we bless sheha'Kol. If it smells like vinegar and tastes like wine, we say Borei Peri ha'Gefen, even if it grew a crust. Regarding Kidush, the Tur discusses when there is no crust. If it smells like wine but tastes like vinegar, even if we would bless Borei Peri ha'Gefen on it, the Halachah depends on the taste, so one may not use it for Kidush. If it has a crust, even if it smells like vinegar and tastes like wine, so we bless Borei Peri ha'Gefen, it is Pasul for Kidush.

Rebuttal (Taz 1): We do not discuss Kanik, for it is Kosher even for Kidush. Wine at the bottom of the barrel, even though it has dregs, can be strained (272:3)! Rather, we discuss Koses; it itself is bad. We do not bless Borei Peri ha'Gefen, for it smells like wine but tastes like vinegar.

Shulchan Aruch (4): If people refrain from drinking it due to its sourness, we do not bless Borei Peri ha'Gefen on it.

Gra (14): Rav Yehudah agrees that we bless sheha'Kol on such wine.

Magen Avraham (14): The Tur (YD 123:8) says in the name of R. Tam that we are not proficient about what is vinegar. There is (a level of soured wine) that some call it vinegar, and others drink it and make Kidush on it! Due to the Safek, one should drink wine with it to exempt it from the Berachah beforehand and afterwards.

Machatzis ha'Shekel (DH Kol): The Magen Avraham teaches that the Shulchan Aruch says to bless sheha'Kol because it is a Safek.

Rebuttal (Bi'ur Halachah): The Magen Avraham is from Sefer ha'Terumos, which the Beis Yosef brought. He does not connote that it is due to Safek! Also the Gra says that the Gemara says that we bless sheha'Kol on this wine. This is not due to Safek, rather, because it changed for the worse.

Kaf ha'Chayim (27): The Beis Yosef says that even though we are stringent if a Nochri touched it (to forbid it, lest it is wine), since people refrain from drinking it, we do not bless Borei Peri ha'Gefen on it.

Kaf ha'Chayim (28): If one blessed Borei Peri ha'Gefen, he was Yotzei.

Shulchan Aruch (272:1): One may not say Kidush on wine that smells bad, even if it smells and tastes like wine.

Beis Yosef (DH u'Bi'ur): Even though we bless Borei Peri ha'Gefen on it, one may not say Kidush on it, for it is slightly putrid.

Gra (1): This is because it is Pasul for Nesachim. If it did not smell like wine.

Mishnah Berurah (2): It smells bad because it was out in a filthy Keli. We say Borei Peri ha'Gefen on it; it is Pasul due to "Hakrivehu Na l'Fechasecha (would your governor accept such a gift?!)".

Bi'ur Halachah (DH Ein): The Ramban says that b'Di'eved he was not Yotzei Kidush. This requires investigation. Such wine may not be used for Nesachim due to Hakrivehu Na. If so, b'Di'eved it is Kosher!

Kaf ha'Chayim (5): B'Di'eved he was Yotzei, for Kidush on wine is only mid'Rabanan.

Mishnah Berurah (1): R. Akiva Eiger was unsure if it is Kosher for Havdalah I say that surely it is not, due to Hakrivehu Na!

Rema: One may not say Kidush on wine that smells like wine and tastes like vinegar.

Taz (3): This is obvious, for we bless sheha'Kol on it! The Tur merely taught it along with wine that smells like wine and tastes like vinegar. The Bach says that we bless Borei Peri ha'Gefen on it as long as there is no crust. This is wrong. This is worse than a crust! However, it seems that whenever the taste is vinegar, it has a crust.

Magen Avraham (2): 'Tastes like vinegar' means that people refrain from drinking it due to its sourness.

Gra (3): We hold that it depends on the taste. Tosfos (96a DH ha'Bodek) says that if it smells like wine, it definitely tastes like wine.

Shulchan Aruch (272:3): One may say Kidush on wine that smells like vinegar and tastes like wine. In any case, it is a Mitzvah to pick good wine for Kidush.

Mishnah Berurah (9): One may say Kidush on it l'Chatchilah, but the ideal Mitzvah is to use good wine.