פירוש על עבודה זרה 132:13

Abaye says that as soon as the wine even begins to fall into the vinegar it will begin to smell like vinegar. The smell of the vinegar will waft up into the wine. A substance is defined by its smell and not by its taste. Therefore this is a case of one species being mixed with the same species and in such cases even the smallest amount of prohibited substance causes a prohibition.

Rava says that even though the wine smells like vinegar, it is wine and therefore this is a case of two different species being mixed together. In such cases the prohibited substance must impart a taste for the mixture to become prohibited.
I should note that were it not for the Talmud I would have explained the debate in a much simpler way. The taste of vinegar is much more pronounced than wine. So when vinegar falls into wine, we can use the taste test. But when wine falls into vinegar it would require a very large amount to nullify the taste of the vinegar. Therefore the taste test won’t really work. So the amoraim debate whether it should be used in any case.

If an idolater smells Jewish wine through a bung hole, the wine is permitted. Such wine was not libated. But a Jew may not, according to Abaye, even smell non-Jewish wine. “Smelling” is considered deriving benefit and deriving benefit from non-Jewish wine is prohibited.

Rava says that smell is not something substantial and proves it from a mishnah that deals with lighting an oven with terumah cumin. The bread baked in the oven has the smell of cumin but not the taste and therefore it is permitted for a non-priest to eat it.

Abaye, who holds that smell is something substantial, responds that the case of the oven is different, for the prohibited substance is consumed by the fire. In contrast, the wine is still present and therefore a Jew may not smell it.

Mari posits that the R. Meir and R. Yose disagree about the same issue that Abaye and Rava do. R. Meir holds that the loaf is prohibited because it absorbs the smell of the wine. Smell is substantial. This is like Abaye. R. Judah permits the loaf because he holds that smell is not substantial. This is like Rava.

Rava would have to admit that he holds only like R. Judah. But Abaye could say that all tannaim agree with him. They only disagree in a case where the smell is not likely to go into the bread, either because the bread is cold or the wine is stoppered. Abaye could say that smelling the wine directly through the bung-hole is again a case in which all tannaim would agree that the smell is substantial enough for the act to be prohibited.
I think people should note how two issues are being conflated in this sugya. Abaye and Rava are arguing whether one is allowed to smell prohibited substances. The issue is whether an action is permitted. In contrast, the sources they bring are discussing whether substances are defined by their smell or not. The issue is status of object. These are not exactly the same issue. I believe that what causes the sugya to discuss them simultaneously is the general rule—smell is substantial or not. This is a classic example of how a general rule allows different subjects to be discussed together and for one to effect the other.