פירוש על עבודה זרה 111:2

The baraita about tithes teaches that even when in the press the liquid can be considered wine once the waste (skins and seeds) has been skimmed off the top. This is even before the liquid flows down to the vat, and thus disagrees with our mishnah.
Rava answers that there is indeed a dispute between the mishnah and the baraita, and it reflects the dispute between the rabbis and R. Akiva. According to the rabbis, the grape juice is not subject to tithes until it descends into the vat. This accords with the mishnah from Avodah Zarah. In contrast, R. Akiva says that it is subject to tithes once it is has been skimmed, even though it is still in the press. This contradicts the mishnah from Avodah Zarah.