Commentary for Bava Batra 6:3
הַמּוֹכֵר יַיִן לַחֲבֵרוֹ וְהֶחְמִיץ, אֵינוֹ חַיָּב בְּאַחֲרָיוּתוֹ. וְאִם יָדוּעַ שֶׁיֵּינוֹ מַחְמִיץ, הֲרֵי זֶה מִקַּח טָעוּת. וְאִם אָמַר לוֹ יַיִן מְבֻשָּׂם אֲנִי מוֹכֵר לְךָ, חַיָּב לְהַעֲמִיד לוֹ עַד הָעֲצֶרֶת. וְיָשָׁן, מִשֶּׁל אֶשְׁתָּקַד. וּמְיֻשָּׁן, מִשֶּׁל שָׁלֹשׁ שָׁנִים:
If one sold wine to his neighbor and it turned sour, he [the seller] is not liable for returns. [For when he sold it, it was wine. This, only if it became vinegar in the buyer's vessels. For, if in the seller's vessels, he (the buyer) can say to him: "Here is your wine and here are your vessels." And the seller cannot tell him: "Why did you leave it in he vessels so long? It is your loss." For the buyer can tell him: "I told you in the beginning that I intended to use the wine only little by little."] And if it is known that his wine turns sour, [i.e., that it does not last; and the buyer told him that he did not need it for wine (i.e., for immediate drinking), but for mikpeh, to be used little by little], it is a "mistaken sale." [For he should have told him that his wine does not "hold."] And if he told him: "I am selling you spiced wine, [which generally "holds" until Shevuoth, after which it spoils, he must supply him (with wine that holds) until Shevuoth.] And [if he sold him wine purported to be] "old," [he gives him wine] from the previous year. And "very old," from three years (before).
Bartenura on Mishnah Bava Batra
English Explanation of Mishnah Bava Batra
If he had said to him, “I am selling you spiced wine”, he is responsible for its remaining [good] until Shavuoth.
[If he said] it is old wine, it must be from last year’s. [If he said] it is vintage old wine, it must be from the year before last.
Mishnah three discusses rules concerning the sale of wine.
This mishnah is concerned with the responsibility of a wine seller to ensure the quality and preservation of the wine which he sells. If he sold him wine and it turned sour, the seller is not in general responsible, since wine is known to turn sour. If, however, the seller knew that the wine would soon turn sour and he did not warn the buyer, the seller is responsible to return the buyer’s money.
If he sold him spiced wine, he is responsible that it not turn sour until Shavuoth. Spiced wine was known to last during the winter but turn to vinegar due to the heat of the summer. Therefore the wine need only last until Shavuoth, the holiday celebrated at the beginning of the summer.
Finally the mishnah clarifies two terms used in the selling of wine. “Old wine” must be from last year’s batch and “vintage old wine” must be from the year before last. If the seller promised one of these types of wine and he gave the buyer wine that was not as old, the buyer can demand his money back.