Khullin 98 Why is the annulment ratio for eggs different?

What is the ratio of permitted taste to annul the forbidden taste in a mixture? Although later on in our daf TB Khullin 98 a disagreement concerning this ratio is presented, the accepted halakha is a ratio of 60:1. There must be 60 times more of the permitted taste to annul the forbidden taste in order to make the mixture permissible to eat. One exception is eggs.

“The Gemara continues its discussion of nullifying forbidden foods. Rav Shemen bar Abba says that Rav Idi bar Idi bar Gershom says that Levi bar Perata says that Rabbi Naḥum says that Rabbi Biryam says in the name of a certain elder, and his name was Rabbi Ya’akov, that the Sages in the house of the Nasi said: If a non-kosher egg is mixed with kosher eggs, if there are sixty eggs they are all forbidden, but if there are sixty-one eggs they are all permitted.

“Rabbi Zeira said to Rav Shemen bar Abba: See, one can infer from your words that you fix a limit to permit the eggs if there is a total of sixty-one eggs, including the non-kosher egg. This is a revelation, because the two most eminent Sages of the generation did not clarify this matter. These two eminent Sages were Rabbi Ya’akov bar Idi and Rabbi Shmuel bar Naḥmani, and both of them said in the name of Rabbi Yehoshua ben Levi: In a case where a non-kosher egg is mixed with kosher eggs, if there are sixty eggs they are all forbidden, but if there are sixty-one eggs they are all permitted.

"And a dilemma was raised before these Sages: When Rabbi Yehoshua ben Levi said they are permitted if there are sixty-one eggs, does that mean there are sixty-one eggs altogether, with the non-kosher egg, or does it perhaps mean that there must be sixty-one kosher eggs aside from the non-kosher egg? And they did not resolve this dilemma. And yet, it appears as though the Master, Rav Shemen, has resolved the dilemma, because you implied that the mixture is kosher if there are a total of sixty-one eggs including the non-kosher egg. “The Gemara continues: It was stated that Rabbi Ḥelbo says that Rav Huna says: If a non-kosher egg becomes mixed with kosher eggs, if there are sixty kosher eggs in addition to that non-kosher egg, the entire mixture is forbidden. But if there are sixty-one kosher eggs in addition to that one non-kosher egg, the mixture is permitted.” (Sefaria.org translation)

We’re used to buying the same size eggs in a carton at the supermarket. Somebody has measured the eggs and put the extra large eggs in one carton and the medium eggs in another. That was not the case in days gone by. Ramban suggests that egg sizes are not uniform. When the purchaser bought a dozen eggs, eggs came in all different sizes. To make sure that the ratio would actually be 60:1, the rabbis bumped up the ratio to 61:1 to compensate for smaller eggs.