Grain, even if it has been roasted, should be kept from contact with water because it may become CHAMETZ (463:3), and the same is true for grain shells (see 465:1-3). On keeping grain from contact with liquids see 466:1-3; on what to do with flour or grain that may have come in contact with water see 466:4,6 and 467:1-7. If grain or flour is used in the production of a food, it may be forbidden to use that food on Passover; for examples see 467:8.
If CHAMETZ becomes mixed (see 447:9) on Passover with any amount of food of any type, it is forbidden to eat or derive benefit from the mixture, and it must be destroyed (447:1;467:9-10,12). We forbid the mixture even when it is caused by absorption without contact, or by absorption in the presence of hot liquid that has not been on a fire, or if the mixture has a bad taste (447:1,3,10). When it is caused by absorption in the absence of liquid, the custom is to destroy only the food that was in direct contact with the CHAMETZ (467:11,14-15); and if the absorption is only on the surface (see Yoreh De’ah Ch.7), only the surface layer becomes forbidden (447:1;467:16). If an object absorbs CHAMETZ, it is permitted after Passover (447:1), and it may be used for non-food-related purposes on Passover (450:7).
A mixture of CHAMETZ that occurs before Passover, even on the 14th of Nisan, is like a mixture containing other forbidden food (see Yoreh De’ah Ch.8), which is usually permitted if the forbidden component is less than 1/60 of the total or gives the mixture a bad taste (447:2). The mixture does not become forbidden when Passover begins, unless additional absorption may have taken place on Passover (447:4). On using salt, wine, or vinegar that may contain particles of CHAMETZ, or utensils that absorbed CHAMETZ, see 447:5-8.
If edible CHAMETZ (see 447:12) is in the possession of a Jew on Passover, even inadvertently, it is forbidden to derive benefit from it even after Passover (448:3) even if the Jew annulled it before Passover (448:5); in particular, it is forbidden to feed it to an animal (448:6-7). A mixture containing such CHAMETZ is like a mixture containing other forbidden food (see above); on what must be done if the CHAMETZ is more than 1/60 of the total see 447:11.
If CHAMETZ was in the possession of a non-Jew during Passover, it is permitted to eat it after Passover (448:1). On accepting CHAMETZ from a non-Jew on Passover see 448:2; on giving or selling CHAMETZ to a non-Jew before Passover with the intent of getting in back after Passover see 448:3-4; on CHAMETZ of uncertain ownership see 449:1; on loans or business transactions involving CHAMETZ see 450:1-7.
Utensils that absorbed CHAMETZ should be cleaned thoroughly and put away safely; they may then be used after Passover, but on Passover they must not be used even with cold food (451:1). A utensil (other than pottery; see 451: 1-2,7-8,22-24,26) that absorbed CHAMETZ on a fire in the absence of liquid may be used with hot food on Passover after heating it to a high temperature; see 451:4. If it absorbed CHAMETZ in the presence of hot liquid, it may be used with hot food on Passover after cleaning it and immersing it in boiling water, but if it cannot be thoroughly cleaned, it must be heated to a high temperature; see 451:5-6. On knives see 451:3; on other specific types of utensils see 451:10-11,16-22,25,27; on handles and covers of utensils see 451:12,14-15; on repaired utensils see 451:13. (On utensils that absorbed other forbidden food see Yoreh De’ah Ch.7.) Heating to a high temperature may be done even on Passover, but immersion in boiling water must be done by the day before Passover, preferably in the morning (see 451:9;452:1), and may be done only to utensils that absorbed CHAMETZ at least 24 hours previously (452:2). For further details about the immersion process see 452:3-7 and 467:13.
Shulchan Aruch, Copyright (c) 2000 Project Genesis, Inc.