פירוש על עבודה זרה 148:10

Mishnah. A vat [for wine-pressing] made of stone that a heathen [sealed with] tar: it was customary to lift a small amount of wine into it [i.e. the vat] to overcome the smell of the tar.

To scour it: [This is] explained in the gemara [as scouring using] water and ashes.

Of wood: which requires more tar since it absorbs more wine [i.e. than a stone vat]. Rabbi says scour it as with the stone [vat] and the Sages disagree.

And of earthenware, even if the tar is peeled off, it is forbidden: one might think every opinion holds this way since earthenware itself without tar absorbs wine.

Gemara. But if he trampled [grapes] in it [i.e. the vat]: without tarring, scouring is not necessary, rather rinsing [is sufficient].

He taught the customary case: because it is the custom of the tar-sealers to throw wine into it [i.e. the vat].

Others say, Raba says only when tarred: [if the vat is tarred, but] he did not trample [grapes] in it, this is the case in which scouring is sufficient.

Cleansing it is not sufficient - rather, peeling [off the pitch entirely is necessary] because wine may enter the cracks in the pitch.

Shi'ah - Smooth.

There are three types of wine presses mentioned by the mishnah: stone, wood and earthenware. Stone is the least absorbent of these materials. Furthermore, stone wine presses do not require much pitch to seal them. Therefore, all the Jew must do is scour the wine press to rid it of any traces of the previous owner’s wine. If the wine press was made of wood, Rabbi [Judah Hanasi] holds that it also may be scoured. However, the Sages hold that he must also peel off all of the pitch. Since wood is more absorbent than stone, and since wood wine presses require more pitch, he must be even more diligent in cleaning before it becomes usable. If the wine press is of earthenware, the Jew may never use it. Since earthenware is very absorbent, there is no way to rid it of the yen nesekh.

Rava emphasizes that scouring is necessary only when the non-Jew covered the winepress with pitch. If he tread grapes without lining the winepress with pitch, the winepress does not need to be scoured. We might have thought that it is always necessary, therefore Rava had to recite his teaching.

According to this version of Rava’s statement, Rava is teaching that scouring is sufficient only if the non-Jew did not also tread his grapes in the pitch-lined winepress. If he also tread grapes in it, the wine is more absorbed and scouring is not sufficient. This is a more stringent version of the teaching.

This is a fascinating story for what it tells us about the role of the rabbi in the Jewish community. A man comes to R. Hiyya and wants to essentially kasher a winepress that he probably bought from a non-Jew. R. Hiyya sends out his nephew to makes sure the kashering process is done well, for otherwise people will complain about R. Hiyya in the Bet Midrash. Rav says that smooth parts of the winepress can be koshered by scouring for they absorbed less of the wine that had fermented in there earlier. But the part that had a crack must be treated more stringently. The outer layer of the press must be scraped down. This is still a principle in koshering things like pots, pans, knives, etc. If the surface is smooth, it is less likely to have absorbed taste.

According to the rabbis, scouring a vessel in order to kasher it is not sufficient. Since we are assumedly dealing with either a winepress sealed with lime or with earthenware vessels, the kashering must be performed by peeling off the outside layer. In contrast, Rabbi agrees that generally scouring is sufficient. However, a vessel used to store wine for a longer period will absorb more and therefore in that case even Rabbi agrees.

Wood and stone are less absorbent than earthenware and therefore all agree that they may be scoured. But a winepress covered with pitch must be kashered by peeling off the outside layerthat had absorbed the wine.

If the winepress had been tread in by the non-Jew, then scouring is not sufficient because it has absorbed more. But if the grapes were not trodden in the press, then scouring is sufficient.

The mishnah rules that earthenware vessels must be peeled in order to kasher them. This is the view of the rabbis. Rabbi [Judah Hanasi] would say that scouring is sufficient.

Rava says that a tank, which probably is another word for the vat into which the wine flows, must be scalded with hot water to kasher it.

Rava was sending empty jars from his place to other Jews in Harpania. He sealed these jars up well (some sort of double-seal) for he feared that the non-Jews with whom he was sending them would use them. Rava was of the opinion that just as the rabbis decreed against wine belonging to non-Jews, so too they decreed against storage vessels used by non-Jews, even for a short period.

How does one scour earthenware vessels? While it might seem that Rav and Rabbah b. Hanah disagree, the Talmud believes that they do not. Both say that one needs ashes (a cleansing agent) and water. If the vat is wet, first he puts some ashes and then he cleans it off with water. If the vat is dry, he first puts some water and then the ashes clean it off.