פירוש על בבא בתרא 6:3

אינו חייב – [the seller in his responsibility] for at the time of the sale, it was wine. And specifically, when it became fermented/sour in the utensils of the purchaser, for if it were in the utensils of the seller [when it became fermented], he (i.e., the purchaser) could say to him (i.e., the seller): “ this is your wine and this your vessel,” and the seller is not able to say to him: “why did you leave it (i.e., the wine) in these vessels so long? You are the one who has taken a loss,” for this one could have said to him: but from the beginning, I informed you that it was not my intention to be supported by this wine, other than a little bit [at a time].”

If a man sold wine to his fellow and it turned sour he is not responsible. But if it was known [to the seller] that his wine would [soon] turn sour, this is a mistaken purchase.
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.

ואם ידוע שיינו מחמיץ – that it is not preserved and the other one says to him that he didn’t need wine, but rather for a stiff mass of grist, oil and onions and to let it stand to take from it only bit by bit.

הרי זה מקח טעות – he should have informed him that his wine does not endure.

מבוסם – it is its manner to endure until Shavuot. But from then onward, the heat spoils it.

וישן – if he sold him wine on the condition that it is old, he gives him from the year before – from the year that past that precedes this one.