In principle, the portion of dough designated as challa is supposed to be given to a kohen to eat. This is one of many ways that the laws of challa are related to the laws of teruma.[1] If teruma becomes tamei (impure), it may not be eaten, and the gemara[2] reasons that just as there is a mitzva to burn kodashim (sacrifices) that are tamei, teruma that is tamei is burned, and this is true of tamei challa as well.[3] All challa is tamei in our days because we all are tamei; although food does not become tamei before it is touched by one of seven liquids, including water, challa, which is taken from dough, is by definition always touched by water. Accordingly, the Rama[4] gives standard instructions to remove a k’zayit for challa and burn it.
Where should one burn the challa? It is forbidden for a non-kohen to eat challa, and one might therefore logically conclude that it should not be burned in one’s regular oven, which obviously needs to remain kosher. The Rama[5] does say that one should make a separate fire to burn the challa, but for an unexpected reason – namely, that a non-kohen must not get any benefit from the heat that the burning challa produces. The Rama continues that the minhag is to burn the challa in the oven before baking the bread. It is important to note that in the Rama’s time, ovens had a separate chamber with fuel and fire, and one could throw the challa in with the fuel. Nowadays, in contrast, gas or electric ovens have one chamber in which items bake and do not usually burn (unless one sets the temperature very high and/or leaves the oven on for a long time). Nevertheless, most poskim seem to prefer burning the challa in the oven to simply discarding it. Why doesn’t baking this forbidden-to-eat food create a kashrut problem?
Indeed, whatever surface touches the hot but not yet burnt challa will need to be kashered, and one should therefore have a separate “treif” tray to put it on. But why don’t the challa vapors pose a problem? While the Shulchan Aruch and Rama[6] rule that reicha (odor) from non-kosher meat does not forbid kosher meat that was roasted in the same large oven, this applies only b’di’eved.
There are two situations in which the issue of reicha is mitigated – when the foods are not fatty and when the two foods are not in the oven at the same time, which is what should be done in the case of burning challa. May we set up this situation in the first place? The Shach[7] maintains that it is permitted to bake Rabbinically forbidden, non-fatty food together with kosher food. (Challa is a Rabbinic law outside of the Land of Israel; in our times, it is Rabbinic even in Israel because a majority of Jews do not live in it.[8]) However, in light of the fact that not all agree with the Shach’s premise, many suggest wrapping the challa in foil. Keep in mind that it takes longer for the challa to burn that way and that the dough expands when heated, so that it may burst through its wrapping before it burns. Many are concerned that the chance of a mishap when burning the challa in the oven is great, as well as inconvenient. (Burning on the stovetop has some advantages, but the smell of burnt bread and the remote possibility of a fire are issues.)
Given these concerns, some say that one may dispose of tamei challa by discarding it in the garbage, after wrapping it to avoid disgracing it. (Some require a double wrap, which seems to be a chumra.) The major justification for this approach is based on an explanation in Rashi[9] that there is no obligation to burn the challa per se; there is simply a need to preclude the possibility that someone will eat it. Accordingly, throwing it out could actually be preferable to waiting for a chance to burn it. Additionally, there are certain circumstances under which it is forbidden to burn teruma/challa, and it is possible to confuse the situations.[10] In this forum, we cannot do justice to the halachic analysis of this view. However, we will say that despite the fact that Rashi’s opinion is the minority and is difficult, use of this option has become increasingly common (including in kosher bakeries) and is accepted by many rabbanim (some of whom suggest other mitigating factors as well). Thus, in the event that one finds it problematic to settle upon a feasible and safe way (both physically and kashrut-wise) of burning the challa, she should not feel guilty if she simply wraps up the challa and discards it in the garbage.