Some substances absorb more easily or less easily than others; for examples see 64:18-19;96:5;121:1. Pressure (as in cutting with a knife or grinding in a mortar) increases the depth of absorption; see 94:7 and 96:1-3 as well as 10:1-3;64:16;89:4.
Even in cases where the forbidden component is less than 1/60 of the total, if it can be recognized or separated it must be removed; and if it is attached to or first entered a permitted component, that component is forbidden and must be removed if it can be recognized (69:11;72:2-3; 73:6;90:1;92:2-4;94:3;98:4;106:1-2). When a permitted food component becomes forbidden because of thorough mixing (see Ch.8a) or absorption it is regarded as entirely forbidden even if it absorbed an amount smaller than its volume (92:4;98:5;99:3,5;106:1;107:2), but if it absorbs meat or milk it is not regarded as being entirely meat or milk (94:6). If an object absorbs an unknown amount of forbidden food it is regarded as entirely forbidden (see 94:2) unless the absorption was of a type that requires only peeling (98:4). If it absorbs a known amount of forbidden food it is not regarded as entirely forbidden unless it is made of pottery or it has also absorbed an unknown amount of permitted food (98:5; see 92:5-7 and 94:6).
Permitted and forbidden foods should not be heated together in an enclosed space (such as an oven) unless one of them is covered or both of them are in containers and the oven is not completely enclosed, but if this was done the food remains permitted if the oven is not completely enclosed unless one of the foods has a sharp taste or unless a mixture containing even a tiny quantity of the forbidden food would be forbidden (90:2;97:3;108:1-2; see Ch.8a). Some foods absorb odors even if the source is covered; see 108:4. Similar laws apply to heating them one after the other if the first one causes steam to form in the oven (108:1; see also 92:7-8;93:1; 105:3). Tasting forbidden foods even without swallowing them is forbidden (108:5), but smelling them is not forbidden unless it is forbidden to derive benefit from them (108:7).
An object that was in contact only with cold, unsalted forbidden food can be cleaned by thorough washing (121:1), but if it has absorbed forbidden food it should not be used even with cold, unsalted permitted food even after it has been washed unless it is earthenware (see 69:16; 94:7;121:5). If an object made of metal, wood or stone absorbed forbidden food in the presence of hot liquid, the absorbed food can be removed from it by immersing it in boiling water at least 24 hours after the food was absorbed in it (91:5;108:3;121:2). If the absorption was in the presence of heavy salt or of hot liquid that is no longer in a utensil that has been on the fire, it is necessary only to scrape off the object’s surface where the food or liquid touched it; see 92:9. If it absorbed forbidden food by heating in the absence of liquid (this includes frying) the absorbed food can be burnt out of it by heating it to a high temperature (97:2;121:4-6). If it is a knife it may be used with cold food after thoroughly cleaning or grinding it down; to use it with hot food it must be heated to a high temperature or ground down and immersed in boiling water (see 10:1-3;64:17;69:20;89:4;94:7;121:7). These laws are also treated in Orach Chayim 55:1-2; see 121:3. On the procedures for cleaning utensils that were used with forbidden wine see Ch.10b.
Shulchan Aruch, Copyright (c) 1999 Project Genesis, Inc.