halacha - Does a b'chor need to fast if he didn't partake in food from the siyum?

If a b'chor attended (or made) a siyum on taanis bechoros but did not partake of any food does he need to fast?

Answer

The OP asks about attending the siyum and only eating later at a different place and time?

The Minchas Yitzchak (vol.9:45) and Rav Elyashav (I heard this from Rav Smith) both say (as do others) that the simchah of the siyum is what releases the fast. Therefore, you may eat later and elsewhere. One idea for this is the Gemara (Shabbos 118) that says when there was a siyum on a masechta, they would make a "yom tov". The entire day was infused with the spirit of the siyum.

Of course, since other authorities seem to require the firstborn to also partake of enough food at the siyum itself, it should be done if possible.

As to the opposite, (if the person missed the siyum, but arrived for the food only) there are poskim that say it does not help (Rav Elyashav above and others) however, according to the Minchas Yitzchak above, and others (Minchas Yitzchak (9:45); Harav M. Shternbuch in Teshuvos v'Hanhagos (1:300) quoting Harav Y.Y. Kanievsky who says that it is customary to be lenient in this matter, provided that the person is really "happy" with the siyum taking place.) It is permitted to be lenient.

Of course it is better to attend the siyum.

However, in both cases, it seems the world is lenient.