1) DEDUCTING A STANDARD AMOUNT FROM DEPOSITED FRUIT
QUESTION: The Mishnah states that when a Shomer returns fruit that was deposited with him, he deducts the amount that that type of fruit normally diminishes within the amount of time that it was in his possession. The Gemara explains that this applies only when the Shomer put the fruit together with his own fruit, and thus it is not possible to determine exactly how much the deposited fruit diminished. Since the total amount of fruit (the Mafkid's and the Shomer's) has diminished, it is assumed that each person's fruit diminished equally.
Why does the principle of "ha'Motzi me'Chaveiro Alav ha'Re'ayah" not apply to this case? Since the Shomer is presently in possession of all of the fruit (he is "Muchzak"), the Shomer should be able to claim that his fruit did not diminish at all, and that all of the decrease occurred in the fruit of the Mafkid. Since there is no clear proof otherwise, the Shomer should be able to deduct the entire decrease (and not just half) from what he returns to the Mafkid.
(a) The S'MA (CM 292:10) writes that, indeed, if the Mafkid gives his object to a Shomer and insists that he must receive in return only his own object, the Shomer may claim that the Mafkid's object may have been the one that diminished or was lost. For example, when a person entrusts his animals, such as his goats, to a Shomer, he certainly wants to receive the same animals back. If the Mafkid gives a goat or goats to the Shomer, and the Shomer places them (or they accidentally become placed) among his own goats and it is no longer evident which ones belong to the Mafkid, and then one of the goats becomes lost, the Shomer may claim that the Mafkid's goat was lost, based on the principle of "ha'Motzi me'Chaveiro Alav ha'Re'ayah."
In contrast, when a person deposits fruit with a Shomer, he does not care whose fruit he receives in return. In such a case, the Shomer is not considered "Muchzak," and "ha'Motzi me'Chaveiro Alav ha'Re'ayah" does not apply. From the moment at which the fruit is deposited with the Shomer and mixed with his own fruit, there are no longer two distinct groups of fruit. The fruit of the Mafkid and the fruit of the Shomer are considered a single group and thus the decrease occurs to the entire group.
(b) The SHA'AREI YOSHER (3:24, DH v'Hineh) questions the explanation of the S'ma and offers a different explanation. He says that since the Mafkid does not mind that his fruit is mixed with the Shomer's fruit, and it is considered as though the Shomer mixed the two groups of fruit with the Mafkid's consent, the act of putting the fruit together is considered an act of a Kinyan of partnership, as the act of mixing fruit together is an act of a Kinyan of partnership (Shulchan Aruch CM 176). Hence, the Shomer and the Mafkid have become joint owners in all of the fruit, and any decrease in the fruit must be distributed equally.
Based on this, the Sha'arei Yosher suggests that if the Shomer mixed the fruit together against the will of the Mafkid (or by accident), they do not become joint owners of all the fruit, and the Shomer indeed may claim that it was the Mafkid's fruit which suffered the entire decrease, based on "ha'Motzi me'Chaveiro Alav ha'Re'ayah." (I. Alsheich)
2) A SHOMER WHO LETS FRUIT DIMINISH BEYOND ITS NORMAL RATE
QUESTION: The Mishnah states that when a Shomer returns fruit that was deposited with him, he deducts the amount that that type of fruit normally diminishes within the amount of time that it was in his possession. The Gemara explains that this applies only when the Shomer put the fruit together with his own fruit, and thus it is not possible to determine exactly how much the deposited fruit diminished. If the Shomer designated a specific place for the Mafkid's fruit, then he returns the fruit in whatever state it is in. This implies that even if the fruit has diminished more than the normal amount, the Shomer still returns it in that state. (The RITVA writes that in such a situation the Shomer must make a Shevu'ah that he was not negligent in protecting the fruit. The TALMID HA'RASHBA adds that he also must make a Shevu'ah that he did not use the fruit for his own personal use.)
Why may the Shomer return the fruit to the Mafkid in its diminished state? Raban Shimon ben Gamliel rules (38a) that when a Shomer sees that the fruit that was entrusted to him is diminishing, he must sell it in the presence of Beis Din in order to prevent the owner from suffering a greater loss. Even the Tana Kama there, who maintains that the Shomer may not sell the fruit, agrees that the Shomer must sell it when the fruit has diminished beyond the normal amount. Accordingly, since the Shomer is obligated to sell the fruit when he sees that it is diminishing more than it normally should diminish, if he does not do so it should be considered negligence and he should be required to compensate the owner for his loss! (See MAGEN AVRAHAM CM 443:5.) Why, then, does the Gemara say that he may return the fruit to the owner in its present state?
(a) The MA'AYANEI HA'CHOCHMAH answers that since fruit rarely diminishes more than its normal amount, the Shomer is not responsible to presume that the fruit has diminished so much.
(b) The NEFESH CHAYAH answers that in the case of the Gemara in which the Shomer "designated for him [the Mafkid] a corner [in which to place his fruit]," the Shomer expressly stated that he did not accept any liability for the fruit, but merely gave permission to the Mafkid to place the fruit in his domain. The Nefesh Chayah cites proof for this from the Gemara in Pesachim (6a) which states that when a Nochri brings Chametz into the property of a Jew during Pesach and the Jew "designates for him a room," the Jew is not obligated to get rid of that Chametz because he has not accepted liability for the Nochri's possessions (as Rashi there explains), but has merely given the Nochri permission to place his items in his domain.
(According to this answer, the Shomer technically is not a Shomer at all, since he did not accept upon himself the obligations of a Shomer. This, however, is not consistent with the Rishonim mentioned above who require that the Shomer make a Shevu'as ha'Shomrim when he returns the fruit that has diminished.) (I. Alsheich)
3) OLD BARRELS THAT NO LONGER ABSORB
QUESTION: The Mishnah (40a) states that old wine barrels do not absorb wine, and therefore a Shomer who placed wine in old barrels may not deduct any wine from the amount that was deposited with him. In the Gemara, Rav Nachman explains that the Mishnah refers to old barrels lined with pitch. Abaye says that even old barrels that are not lined with pitch do not absorb wine, because once they have absorbed their fill they no longer absorb any more wine.
The Acharonim question this Gemara from the well-known principle in the laws of Isur v'Heter that when a prohibited food item is cooked in a pot, the pot absorbs the item and it, too, becomes prohibited to be used. With regard to that principle, no distinction is made between an old pot and a new pot. According to Abaye, an old pot should no longer be able to absorb additional food and thus it should not become prohibited! (TAZ YD 93:2, KEREISI U'PLEISI there, and others)
(a) The TAZ (also cited by the Pnei Yehoshua here) answers that the Gemara here is correct that an old pot does not absorb additional material, yet it is also true that an old pot becomes prohibited when a prohibited item is cooked in it. He explains that the act of cooking causes the pot to expel some of the material its walls have absorbed, and this creates room to absorb the prohibited material. That is why the pot becomes prohibited.
The same occurs when wine is stored in an old barrel. When wine is soaked for a long period of time, this causes the barrel to expel some of the wine that it has absorbed already, thus making room to absorb new wine. The total amount of wine in the barrel, though, remains the same. That is why the Shomer may not deduct any wine when he returns it to the owner.
(The IMREI MAHARSHACH points out that according to this answer, if the barrels had previously been used to hold water, then now the barrels would have expelled water and absorbed wine. He answers that people are not normally particular about this, since the presence of such a small amount of water in the wine is immaterial.)
(b) The KEREISI U'PLEISI and CHAVOS YA'IR (#104) answer that it is true that an old pot or barrel does not absorb any liquid or food material. However, it does absorb taste ("Ta'am"). A pot in which a prohibited food was cooked absorbs the taste of that food and becomes prohibited. "Taste" is absorbed by a pot even if the pot has already absorbed its capacity of liquid or food material.
(The CHAVOS YA'IR adds that the concept of the Gemara here, that once a barrel has absorbed its capacity it no longer absorbs more, applies only to earthenware vessels. Wooden vessels, in contrast, always absorb more. This is the subject of discussion among the Acharonim.) (I. Alsheich)