פירוש על עבודה זרה 131:15

Old wine has a taste very different from grapes. Therefore when it falls on the grapes, all agree that the grapes are prohibited only if the wine imparts taste.
However, new wine will taste like grapes. Therefore there is a dispute about this issue—Abaye says that the grapes are prohibited even if there is only a very small amount of wine, whereas Rava says that for the grapes to be prohibited they must impart taste.

Abaye says that new wine mixing with grapes is a case of “one species being mixed with the same species,” since they both have the same taste. When two of the same species are mixed, the mixture is prohibited even if there is only the smallest amount of prohibited substance. After all, if they taste the same, how can one detect the presence of the forbidden substance.

Rava follows the name of the substance, not the taste. New wine has a different name from grapes and therefore for the wine to prohibit the grapes it would have to impart taste. Note that it would in reality be impossible to test for this because they have the same name. Therefore the only criteria would be to determine an actual amount of wine that needs to fall on the grapes. This is where the notion of 1/60th comes into play. If there is 60 times as much permitted substance, the mixture is permitted. But if less, it is prohibited.

The mishnah says that if the grapes are cracked, they are prohibited. The Talmud makes two assumptions: 1) this is new wine, which has the same taste as grapes; 2) the grapes are prohibited only if the wine imparts taste. This then rejects Abaye.

The problem with assuming that the grapes are prohibited even if a small amount of wine falls on them, is that the end of the mishnah clearly shows that the mishnah is referring to cases where the mixture is prohibited only if the prohibited substance imparts taste. Therefore, the mishnah does seem to be a difficulty on Abaye who prohibits the grapes even if a small amount of wine falls on them.
But, no worries, Abaye can resolve the mishnah by saying it refers to a case of old wine that falls on grapes. Since the old wine has a different taste, the grapes are prohibited only if one can taste the wine.

Wine and grain vinegar have the same name but different flavors, as do wheat and barley yeast. To Abaye these are different species because categorization is done by taste not name. Therefore the prohibition is prohibited only if the forbidden substance imparts taste.

Rava says that since these substances have the same name they are considered the same species. Even the smallest amount of prohibited substance causes the whole mixture to be prohibited.

Rava says that this baraita follows R. Meir. Other sages do not hold that forbidden substances with different names join together because we follow the name, not the taste.

Abaye uses a baraita that is explained by Hezekiah to prove that a substance is defined by its taste. If three different spices with different names that are all forbidden (for instance they are all orlah—produce during its first three years) fall into a pot and each one of them is not sufficient to impart taste but together they impart taste the dish is prohibited. This is because they all taste the same. The fact that they have different names does not matter.

In this case Abaye and Rava both agree that these are two different substances—different names and different tastes. Therefore the wine is prohibited only if the vinegar imparts taste.

The two sages debate if wine falls into vinegar. Abaye says that even if the wine does not impart taste it causes the vinegar to be prohibited. Rava says that the wine must impart taste. The Talmud shall now explain their reasoning.

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.