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One of the major topics in the laws of Pesach that appear in the Shulchan Aruch [chapters 442 and 447], is the law of a mixture that had a Chametz ingredient fall inside, or had Chametz taste penetrate them through use of a Chametz vessel. In some cases, the food becomes forbidden to be eaten/owned, and in other cases the Chametz is nullified and the food remains permitted to be eaten/owned on Pesach. It is beyond the scope of this book to enter into the complexity of these laws, and if in truth a question does arise, one must forward it to a practicing Rav who is competent in this area of Jewish law. Nonetheless, some of the general rules of this law will be mentioned here. A thorough and detailed analysis on these laws can be found in our corresponding Sefer “A Semicha Aid for learning the Laws of Pesach”
Taaruvos Chametz-Foods that had a Chametz ingredient fall into them:
Chametz fell before Pesach: If Chametz became mixed into one’s Pesach food prior to the night of the 15th, then whether or not the food remains permitted in eating/owning depends on several factors, as explained in Chapter 2 Halacha 1H.
Chametz fell on Pesach: If Chametz became mixed into one’s Pesach food from the night of the 15th and onwards, and cannot be removed, or has transferred taste, then the food is always forbidden to be eaten and owned, as explained in Chapter 2 Halacha 1H.
Keli Sheiyni/Shelishi: On Pesach itself, we are stringent to suspect for those opinions who rule that a Keli Sheiyni and even a Keli Shelishi or Revi’i have ability to transfer taste. Thus, if hot Chametz that is Yad Soledes fell onto a food on Pesach, the food is forbidden even if the Chametz was a Keli Revi’i and one is able to separate the Chametz from the food. Nevertheless, in a time of need, such as a great loss or for the sake of Simchas Yom Tov, one may be lenient in a case of Iruiy Keli Sheiyni and onwards to simply wash the Chametz off the food, in all cases that doing so is possible. [For example, if a gentile spilled his hot instant noodle soup onto a Jew’s produce, then since the produce may be washed clean of the Chametz, one may be lenient in a time of need, as stated above.]
Cold Chametz: Cold Chametz that has contacted a Pesach food before Pesach does not have ability to prohibit the food, and it suffices to simply wash the food from the Chametz. However, from the night of the 15th and onwards it is disputed if it has ability to prohibit the food, and the final ruling is to be lenient, unless one’s custom is to be stringent, in which case one is to abide by the custom. [Thus, if a beer spilled onto Pesach produce, it suffices to simply wash it off. If, however, this occurred on Pesach, those who are accustomed to be stringent may not eat it. Likewise,] if one found a kernel of grain in the water in which his chicken was soaking, the chicken remains Kosher, unless this occurred on Pesach itself and one is accustomed to be stringent.
Pesach foods that were cooked or prepared with Chametz vessel:
Cooked in Chametz pot before Pesach: Food that was cooked in a non-Ben Yomo Chametz pot prior to the night of Pesach, and was supervised for the sake of Pesach, is permitted to be eaten on Pesach. If the food was not supervised for the sake of Pesach, then the food is forbidden. If the food was supervised, but was cooked in a Ben Yomo Chametz pot, then it is disputed amongst the Poskim if the food is permitted to eat on Pesach. Practically, we are stringent, and one may not eat the food on Pesach.
Cooked in Chametz pot on Pesach: Food that was cooked in a Ben Yomo Chametz pot on Pesach, from the night of the 15th and onwards, is forbidden in all cases. If the pot was not Ben Yomo, then it is disputed in Poskim as to whether the food is permitted, and practically, the Ashkenazi custom is to be stringent.
Used Chametz spoon or fork for hot food: If one used a clean, non-Ben Yomo, Chametz eating spoon or fork to mix a hot food on Pesach, the food remains Kosher. If, however, the spoon or fork was dirty, or Ben Yomo, or was a serving spoon/fork as opposed to an eating fork/spoon, then the food is forbidden.
Used cold Chametz vessel for cold Pesach food: If Kosher for Pesach foods were placed on a clean Chametz vessel or surface, the food remains permitted, so long as it did not soak in the vessel within liquid for 24 hours. Nonetheless, initially one may not place Pesach foods in a Chametz vessel unless the vessel is not made of earthenware, and it occurs on mere occasion, and is verified to be clean.
Used Chametz knife for Pesach foods: If a cold non-Charif Kosher for Pesach food was cut with a clean Chametz knife, the food remains permitted. [Thus, fresh meat, poultry or fish that was cut with a Chametz knife may be eaten on Pesach.] If the knife was not clean, or one is unsure, it suffices to rinse the food in water. If the food is absorbent, then one is to scrape off the exterior area that the knife touched. If the food is a Charif, such as onions and garlic, then the food may not be eaten on Pesach. [If the food was hot, and was cut with a Chametz knife on Pesach, it is forbidden to be eaten.]
Placed hot Pesach pot on Chametz surface: If one placed a hot and dry Pesach pot with food on a clean and dry Chametz surface, the food is permitted, as long as there was no fat or oil on the surface.
Placing Pesach foods on a covered Chametz surface: A clean and dry Chametz surface which is covered with metal, such as tinfoil, may have even a hot Chametz food placed on top of it. Thus, one may line a non-Kasherable Chametz counter with tinfoil or PVC and then be allowed to place one’s Pesach dishes on it.
 See Admur 451:34
 Admur 467:29-30
 In general we rule that cold foods do not transfer taste. However, some Poskim rule that cold foods transfer a Mashehu taste, and since on Pesach itself, Chametz prohibits even Bemashehu, therefore it prohibits the food. [Admur ibid; Michaber 467:12]
 Admur 447:18
 Admur 447:43
 Some Poskim rule the food remains permitted to eat on Pesach, as its Nat Bar Nat Lehetera. [1st opinion in Admur 442:8] However, other Poskim rule it is forbidden to be eaten on Pesach, if the food does not contain 60x the pot, as the leniency of Nat bar Nat only applies in a case of meat and milk where a new prohibition is to be made. [2nd opinion in Admur 442:8] Practically, we are stringent, and one may not eat the food on Pesach. [Admur 442:8; See also 447:45]
 Admur 442:8; See also 447:45
 Admur 447:18
Placed Chametz cover on Pot: See Admur 451:40
 Some Poskim rule that although Chametz on Pesach is not nullified even in 1000, nevertheless, if the Chametz taste gives a spoiled taste to the food, then the food is permitted. This applies whether its spoiled taste is felt in the dish [no 60x] or whether it is not felt in the dish [there is 60x], as any taste which [is spoiled or] which spoils a food is not considered to be a taste at all, and it is thus considered as if no taste has entered the food. Other Poskim, however, rule that since on Pesach Chametz is not nullified even in a ratio of 2,000,000x, in which case there is no greater level of nullification of Chametz taste, and nevertheless it is prohibited, therefore here too even when the Chametz taste is spoiled it forbids the food to be eaten or benefited from. This applies whether the spoiled taste can be felt in the dish or cannot be felt, even if it’s a ratio of 1:2,000,000. Practically, the main Halachic opinion is like the former opinion, however the custom in these provinces is like the latter opinion. However, in a place that there is no accepted custom then one may be lenient like the former opinion, although one who is stringent even in this case is blessed. [Admur ibid]
 Admur 451:33
 See Admur 447:27; 451:2 and 43
 If one did not verify the cleanliness of the Chametz vessel: From the letter of the law, the above allowance applies even if one did not verify the cleanliness of the vessels a general vessel is considered to be clean of any Chametz beiyun. However, some people beware from using any Chametz vessel for Pesach foods starting thirty days before Pesach, unless the vessel was washed and cleaned well in a way that has been verified to not contain Chametz. If one went ahead and used a Chametz utensil prior to verification, then these people are stringent to not eat that food on Pesach. [Admur 447:51]
 Admur 447:57
 Admur 447:59
 Admur 451:67
 See Chapter 9 Halacha 5
 See Admur 447:9-10
 The reason: As even if the oven is clean and not Ben Yomo, we prohibit foods cooked in a non-Ben Yomo pot on Pesach.