Drinking Mashkeh of non-frum people after Pesach:
- Example: After Pesach, one was offered a beer by a non-religious friend or relative. May one drink it?
Chametz that was owned by a Jew during Pesach: Complete Chametz that was owned by a Jew over Pesach, or that a Jew had liability over during Pesach, is forbidden in benefit for all Jews after Pesach. This applies whether it was owned throughout the entire Pesach, or was only owned through part of Pesach [such as he acquired it from a gentile on Pesach], and applies even if it was only owned for the last part of the last day of Pesach in the Diaspora. This applies even if the owner of the Chametz was not at fault for owning it, being that he was not able to destroy it, or did not know at all that this Chametz was in existence until after Pesach, nevertheless the Chametz is forbidden in benefit [for all]. [Thus, any Jew who did not perform Mechiras Chametz, all Chametz that was in his possession anytime during Pesach is forbidden in benefit for all Jews even after Pesach.]
Chametz that is questionable if it was owned by a Jew: Any Chametz that is Halachically questionable if it forbidden after Pesach, such as it is questionable if it was owned by a Jew, or if it was disowned by a Jew before Pesach, is permitted in benefit, although is disputed amongst the Poskim as to whether it may be eaten. Some Poskim rule the Chametz is permitted even to be eaten. However, other Poskim rule that any Chametz in which there is question as to whether it was owned by a Jew during Pesach or disowned by a Jew before Pesach, is forbidden to be eaten, although is permitted in benefit. Practically, one is to be stringent like the latter opinion not to eat the Chametz, unless it’s a case of great loss [and the Chametz cannot be sold]. According to all, one may benefit from the Chametz.
B. The law:
If one knows for certain that the Jew purchased the Chametz before Pesach, then it is forbidden to be eaten. If one is unsure as to when it was purchased, then this matter is subject to the dispute mentioned above, and practically, one is to be stringent.
 Admur 448:1; Michaber 448:3; Mishneh Pesachim 28a
 Literally “complete grain”
 Chametz of a child: It is questionable whether Chametz that was owned by a Jewish child over Pesach is forbidden in benefit. [See Piskeiy Teshuvos 448:3]
 Admur 440:17; See chapter 2 Halacha 5C!
 The reason it is forbidden for all Jews: As the sages fined the owner of the Chametz due to the fact that he transgressed Baal Yiraeh and Baal Yimatzeh, and the sages did not want to differentiate in their decree between the owner and others and thus forbade it for everyone. [Admur ibid; M”A 448:3; Rava Pesachim 29a]
 Admur ibid; M”A 448:1; Chok Yaakov 448:7; Tur; Baal Haittur 2:126
Conservative Rabbi: Thus, if a conservative/reform Rabbi sold Chametz for his congregation, then even if he did all the sale laws properly the Chametz is forbidden on Pesach if he buys it back on the last day of Pesach in the Diaspora.
 Admur ibid; Michaber ibid; Rambam 1:4
The reason: They forbade it in benefit even in such a case in order to prevent people from leaving over their Chametz until after Pesach and then claiming that they were unable to destroy it. [ibid]
 Admur 448:30
 1st opinion in Admur ibid; Taz 449:1; Chok Yaakov 449:1
 The reason: As by every Rabbinical prohibition, when there is doubt we are lenient. [Admur ibid]
 2nd opinion in Admur ibid; M”A 449:2; Bach 449
 So is evident from M”A ibid and Bach ibid based on Eiruvin 64b as explained in Machatzis Hashekel, and so is implied from Admur ibid as even Chametz that was disowned before Pesach he defines as “Sheavar Alav Hapesach”
 Vetzaruch Iyun if one can rely on the statement of the Jew as to when he purchased the Chametz.