On Pesach, we are very meticulous regarding the prohibition of chametz – far more so than other kashrut-related prohibitions. One of the contributing factors is that chametz has no nullification. The Gemara, Pesachim 30a, concludes that even if a small amount (mashehu) of chametz is added to a mixture, the whole mixture is prohibited. This article will present two approaches to understanding this stringency and the practical differences between the two approaches.

The Two Approaches
Rabbeinu Asher, Pesachim 2:5, states that the reason for the prohibition of mashehu is due to the stringency of the prohibition of eating chametz. The Torah (Shemot 12:16) states that the punishment for one who eats chametz on Pesach is kareit (cutting off of the soul). This is not true of other kashrut related prohibitions. Because the penalty for eating chametz is so extreme, the rabbis instituted that chametz cannot be nullified in a mixture.

Ran, Pesachim 7b, s.v. U'Mid'lo, suggests that the reason for the prohibition of mashehu is based on the principle of davar sheyesh lo matirin (an item that has a method to become permissible). The Gemara, Beitzah 3b, states that if there is a prohibited food that was added to a mixture composed of mostly permitted food, and the prohibited food will become permissible at a later point in time, then that food is not nullified, and retains its prohibited status, thus causing the entire mixture to be forbidden.. Ran explains that chametz that is mixed into a mixture will certainly be permissible after Pesach. Therefore, based on the principle of davar sheyesh lo matirin, one may not eat an item that has even the slightest amount of chametz in the mixture. Rambam, Hilchot Ma'achalot Asurot 15:9, also attributes the prohibition of mashehu to the principle of davar sheyesh lo matirin.

Rabbeinu Asher's reason stems from a ruling of his regarding eating food on Erev Pesach in the afternoon that has a small amount of chametz mixed in. The Gemara, Pesachim 5a, states that there is a biblical prohibition forbidding the eating of chametz on Erev Pesach in the afternoon. Rabbeinu Asher states that since the prohibition of eating chametz on Erev Pesach does not carry the penalty of kareit, a mixture with a small amount of chametz is not prohibited. P'ri Megadim, Orach Chaim, M.Z. 447:1, notes that Rambam (and Ran) would disagree. According to Ran, the davar sheyesh lo matirin principle would apply since the mixture will become entirely permissible after Pesach.

Rabbeinu Asher further notes that if the mixture contains less the one-sixtieth chametz prior to Pesach, it is permissible eat the mixture on Pesach. Rambam, Hilchot Chametz U'Matzah 4:12, implies that there is no distinction between a mixture that was created before Pesach and a mixture that was created on Pesach. They are both equally prohibited.

Rabbeinu Asher and Rambam are internally consistent regarding the prohibition of mashehu. Rabbeinu Asher views the prohibition as an added stringency of chametz and therefore, there is room to distinguish between mixtures that were created at the time of the prohibition and mixtures that were created prior to the time of the prohibition. Rambam, on the other hand, is of the opinion that the prohibition of mashehu is based on davar sheyesh lo matirin, and cannot make this distinction because regardless of when the mixture was created, the mixture will become entirely permissible after Pesach.

Dry Mixtures
Rabbeinu Asher, Avodah Zarah 5:30, rules that the mashehu prohibition only applies to mixtures that are liquid or are cooked together. Dry mixtures are not subject to the mashehu prohibition. [For example, if a matzah that is not kosher-for-Passover was mixed into many matzahs that are kosher-for-Passover, Rabbeinu Asher would permit eating all of the matzahs.] Rabbeinu Asher explains that the stringency of mashehu was only instituted for mixtures whose standard of nullification would have otherwise been one-to-sixty. However, dry mixtures, whose standard of nullification is one-to-two, are not subject to the mashehu prohibition.

Rif, Avodah Zarah 37a, implies that even a dry mixture is subject to the mashehu prohibition. Beit Yosef, Orach Chaim 447:9, explains that Rif is of the opinion that the mashehu prohibition is a function of chametz as a davar sheyesh lo matirin. Therefore, there is no reason to distinguish between dry mixtures and liquid (or cooked) mixtures.

Prohibited Benefit
The Mishna, Pesachim 21a, states that it is prohibited to benefit from chametz. Rabbeinu Asher, Avodah Zarah 5:30, rules that it is likewise prohibited to benefit from a mixture that contains a small amount of chametz. Rabbeinu Asher cites the opinion of Ra'avad who disagrees and maintains that one may benefit from such a mixture (if the mixture contains less than one-sixtieth chametz).

Perhaps the dispute is based on the two approaches presented previously. Rabbeinu Asher is of the opinion that the stringency of mashehu was applied equally to the prohibition to eat chametz and to the prohibition to benefit from chametz. However, Ra'avad is of the opinion that the prohibition of mashehu is based on davar sheyesh lo matirin. R. Yechezkel Landa, Tzelach, Pesachim 4a, notes that the davar sheyesh lo matirin only applies in a situation when one must choose between using the item during its prohibited time or its permissible time. If it is an item that can be used multiple times, the principle of davar sheyesh lo matirin does not apply, since the user would like to benefit during the time of the prohibition as well as after the time of the prohibition. Based on the comments of R. Landa, one can suggest that one can only apply davar sheyesh lo matirin to prohibit eating a mixture that contains chametz, since one has the option of eating the item after Pesach. However, one cannot generally apply davar sheyesh lo matirin to prohibit benefit from an item that can be used multiple times.

Chametz that Fell into a Reservoir
Many municipalities receive their water supply from bodies of water that are accessible to the public. It is quite common for people to throw bread or beer bottles into the water. Should one assume that the entire water system is now prohibited because of the trace amounts of chametz that are present in the water?

The Acharonim present leniencies that satisfy both of the approaches we discussed above. R. Yoav Y. Weingarten, Chelkat Yoav, Orach Chaim no. 18, suggests a solution to the problem based on the idea that prohibition of mashehu is a function of davar sheyesh lo matirin. Based on the aforementioned comment of R. Landa, R. Weingarten posits that mashehu would not apply to a body of water. The prohibition of mashehu applies to an individual item that a person could potentially consume at one time. Regarding a reservoir, the people of the municipality are interested in partaking of the water on Pesach as well as after Pesach. Therefore, the principle of davar sheyesh lo matirin does not apply, and one does not have to be concerned for the trace amounts of chametz in the water.

The approach presented by R. Weingarten assumes that the prohibition of mashehu is a function of davar sheyesh lo matirin. He does not solve the problem of the reservoir if one follows the opinion of Rabbeinu Asher that the prohibition of mashehu is a function of the severity of eating chametz. Nevertheless, this issue is addressed by R. Yehuda Landa, Yad Yehuda, Yoreh De'ah 105:1. He claims that mashehu prohibition was imposed out of concern that the ratios of a mixture containing a small amount of chametz may change and the new ratio will not contain the necessary sixty-to-one ratio of permissible items to chametz. Although we do not have this concern in other areas of kashrut, the stringency of chametz demands a higher standard. R. Landa posits that in a municipal water system, where it is virtually impossible for the chametz content in the water to be more than one-sixtieth, there is no concern for the prohibition of mashehu.