# It is important to buy an etrog that has a reliable hechsher in order to be sure that is not grafted. <ref>The Rama (Responsa 226) writes that an etrog that is the product of an etrog tree grafted with a lemon tree is invalid because it no longer qualifies as an etrog. The Levush (649:4) writes likewise but for a different reason. He asserts that a grafted etrog is invalid since it was created in violation of kilayim (grafting trees of different species) even if a non-Jew did it. The Shevut Yaakov (1:36) disagrees with the Levush’s reasoning, since we hold that non-Jews are not obligated in the laws of kilayim. The Shevut Yaakov quotes a story in which the Shach permitted making a bracha upon a grafted etrog, but he adds that the Shach later retracted. In sum, almost all poskim consider a grafted etrog to be invalid, including the Magen Avraham (648:23), Taz (648:3), and Chazon Ovadia (p. 223). Rabbi Zvi Sobolofsky (“The Laws of the Daled Minim,” min. 3) advised getting an etrog with a reliable hechsher in order to make sure that it is not grafted. </ref>
# An etrog must be at least the size of an egg. <ref> See Mishna (Sukkah 34b), Rambam (7:8), and Shulchan Aruch (648:22). </ref>
# A hole of any size invalidates the etrog. Many poskim hold that it is not an issue if only a piece of the outermost peel is removed, while some say that it is acceptable even if a piece of the thin yellow peel is removed. <ref> The Mishna (34b), according to Rashi, states that an etrog that is punctured and lacking even a little bit is invalid. If, however, it is punctured but not lacking, it remains valid. The Gemara (36a) limits the leniency of the Mishna to where the hole does not penetrate all the way through the etrog and the hole is not the size of an issar coin. The Rosh (3:18) agrees with Rashi. Rabbeinu Chananeil, though, maintains that the Gemara’s limitation was regarding the stringency of the Mishna. Thus, in his view, the Gemara means that an etrog that is punctured and lacking is invalid only if the hole goes all the way through or is at least the size of an issar coin.
* The Rambam (8:7, as understood by the Beit Yosef 648:2) explains the Mishna as meaning if an etrog is punctured or lacking it is invalid, unlike Rashi. For all practical purposes, though, the Rambam agrees with Rashi, because he explains the Gemara as referring to the first case, like Rabbeinu Chananeil, thus limiting the stringency of the Mishna to where the hole goes all the way through or is the size of an issar coin. Though the Rif (17b) is not clear, the Beit Yosef suggests that he agrees with the Rambam.
* The Gemara (35b), according to the explanation of the Rabbeinu Chananeil and Rosh (3:17), establishes that an etrog that is peeled in its majority is invalid, while an etrog that has only a minority peeled is valid. The Ran (17a s.v. Niklaf) explains that the Gemara is discussing a case where the outermost peel (which is thin like frost) is removed. If, however, the thin yellow peel is removed, the etrog would be invalid, as it is an etrog that is lacking. The Rambam (8:7, as understood by the Bach) agrees that it is valid only if none of the thin yellow peel was removed. The Rashba (Responsa 1:58), however, says that it is invalid only if part of the thick white section is removed (see the Machon Yerushalayim edition of the Tur 648 note 13).
* The Bach concludes that the view of the Ran should be normative. Shaar Hatziyun (648:27) elaborates upon the Bach (see also Beiur Halacha 645:2). The Chazon Ish (147:1), however, claims that there never was a dispute and everyone really subscribes to the view of the Rashba. See Mishna Brurah (648:26), who discusses the status of an etrog if the area where the outermost peel was removed became discolored.
* The Terumat Hadeshen (Responsa 99) writes that if a hole was made while the etrog was growing but the flesh and peel subsequently grew over it, it is valid. Rama (648:2) agrees. </ref>
# If the pitom falls off or the stem on the bottom of the etrog is completely removed, the etrog is invalid. <ref> The Mishna (34b) establishes that if the pitom fell off an etrog, the etrog is invalid, but if the oketz fell off, it is valid. The Gemara (35b) explains that the pitom is the rod-like protrusion (“buchanto”). Rashi (s.v. Tani) cites a dispute between his teachers about how to explain what the pitom and oketz are. Rabbeinu Yaakov explained pitom as the protrusion on top of the etrog and the oketz as the thick stem on the bottom. Rabbeinu Yitzchak, however, explained that oketz refers to the outer part of the thick stem on the bottom, while pitom refers to the inner part of that stem, meaning that the etrog would be invalid only if the stem on the bottom is totally removed, even the part that penetrates the etrog. Rashi sides with Rabbeinu Yaakov.
* The Rabbeinu Chananeil (36a) explains that the Gemara was not explaining the Mishna at all but rather adding another potential disqualification. According to his view, the pitom is on the top of the etrog and “buchanto” is on bottom. He adds that the oketz is the outer part of the stem on bottom, and if that is removed, the etrog remains valid. The Rif (17b) and Rambam (8:7) agree. The Rosh (3:16) writes that the minhag was to follow Rabbeinu Chananeil. Shulchan Aruch (648:7-8) concurs. Mishna Brurah (648:31) writes that if the bud on top of the pitom falls off, one should avoid using the etrog unless it is the nicest one available.
==A Punctured Etrog==
# An Etrog which is punctured through and through is invalid. Some say that it is valid as long as no part of the flesh of the Etrog is lacking. Only in extenuating circumstances may one rely on the second opinion. <ref>S”A 648:2 writes that an Etrog which is punctured completely is invalid, however, some say that it is valid as long as it isn't lacking. Mishna Brurah 648:9 writes that we hold like the second opinion in extenuating circumstances. </ref>
# An Etrog which is punctured up until the inner chamber where the seeds are but doesn't go through completely, some say it is invalid and others argue. <ref>S”A 648:3. Mishna Brurah 648:23 writes that one should be strict not to use an Etrog which is punctured up until the inner chamber, unless it isn't possible to find another Etrog, in which case one may be lenient especially if the Etrog isn't lacking.</ref>