Why should the fact that the food is a Biryah determine whether or not its
outer protective shell is considered a Shomer?
(a) In general, the significance of a Biryah comes from the fact that a
whole entity is a more important item than a piece of something the same
size. We find this concept in Makos (17a) with regard to the Isur of eating
bugs. One who eats an entire bug transgresses the Isur of eating bugs,
regardless of its size. In contrast, one who eats part of a bug is not
punished unless he eats the amount of a k'Zayis. The Gemara there clearly
states that this is because a Biryah (a whole bug) is considered important.
Rebbi Shimon in Makos extends this to a grain of wheat, stating that one who
eats a grain of wheat from which Terumos and Ma'aseros have not been
separated has fully transgressed the prohibition of Tevel, even though he
has eaten less than a k'Zayis.
However, this does not seem to be the opinion of RASHI here (119b, DH
Chitim). The Gemara discusses whether or not two Shomrim can combine with
the food to make a k'Beitzah. Rashi explains that the Gemara seeks to prove
from Tana d'Vei Rebbi Yishmael that the husks (in the plural) of a grain of
wheat or barley become part of the grain so that it can be Mekabel Tum'ah.
This shows that two Shomrim can combine. The Gemara responds that these
husks are not Shomrim, but rather Yados. Rashi explains that the Gemara
could have answered this proof the same way it did previously, saying that
although the husks are Shomrim, Tana d'Vei Rebbi Yishmael is referring to
Shomrim of a Biryah, and it is only a Biryah that can have two Shomrim that
combine.
The RASHASH and TIFERES YAKOV have difficulty with Rashi's explanation.
Earlier, when the Gemara discusses how large a food must be in order for its
Shomer to be considered a Shomer with regard to the laws of Tum'as Ochlin,
the Gemara says that the food can be even smaller than a bean as long as it
is a Biryah. In the Gemara here, where the issue is whether or not two
separate Shomrim can be combined, what difference does it make whether the
food that they protect is a Biryah or not? The question of two Shomrim seems
to be whether or not a food can have two "guards." If it is possible to have
two "guards," then even if the food is not a significant size, it should be
able to have two Shomrim! If, on the other hand, it is not possible for an
item to have two Shomrim, then even a Biryah should also not have two
Shomrim. Why should the logic of Biryah make a difference in this case?
Due to this question, the TOSFOS HA'ROSH here explicitly argues with Rashi
and says that this is the reason why the Gemara later (119b) does not give
the answer of "Biryah." This also seems to be the reason behind the
statement of the CHIDUSHEI HA'RAN who states that it is understandable why
the Gemara (119b) does not give the answer of Biryah.
(b) The CHIDUSHIM U'VI'URIM suggests that Rashi understands that the logic
of Biryah in the Gemara here is entirely different. When the Gemara answers
that the Shomer of a Biryah is considered to be a Shomer even though the
food is less than the size of a bean, this is not because a Biryah is
important. The Gemara is saying that because the grain was created with a
husk guarding it, the husk was "born to be a Shomer" for this grain. A food
that has a protective covering that was not created with it must be the size
of a bean in order for the covering to be considered a Shomer.
According to this explanation, we can understand the words of Rashi later
(119b) when he says that when something is "created" with two husks, they
are automatically called Shomrim as they were created as such.
However, the Chidushim u'Vi'urim himself rejects this possibility. The
Mishnah in Ukztin (2:4; see BARTENURA there) teaches that an onion cannot
have two Shomrim, even though its peels were created this way.
He concludes, therefore, that these words must have been inserted into
Rashi's commentary and are not part of Rashi's commentary. This is
consistent with the SHITAH MEKUBETZES who writes that he did not find this
statement in Rashi's manuscript. (Y. Montrose)