This Halacha is an excerpt from our Sefer
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The definition: Chametz Nuksha is dough that is not fit for eating, unless in a pressing situation. An example of such dough, is dough which has begun the leavening process, but has not reached its completion. Such dough, even when baked, will not be fit for eating, unless in a pressing situation, as it is very sour due to its incomplete rising. Similarly, dough which is made by book binders for the sake of attaching papers together, is not fit to eat when baked [unless in a pressing situation], as it is made from the flour-dust of the mills. The same applies to all similar cases [that the dough is not really edible when baked, due to its rising, or flour consistency]. All these examples of dough are called Chametz Nuksha.
The law: Chametz Nuksha is Biblically permitted to be eaten on Pesach, as it is not considered Chametz at all. However, it is Rabbinically forbidden to be eaten or benefited from. The Sages also required one to destroy it before Pesach, [and it is thus forbidden to be owned just like actual Chametz].
 Admur 442:20 and 459:13; M”A 442:1; Pesachim 43a and Mishneh 48b
 Admur ibid; Pesachim 42a-43
 Lit. not fit for eating unless is time of dechak
 Admur ibid; Mishneh 48b; Pesachim 43a
 The reason: As the Torah only forbade complete Chametz [i.e. Chametz Gamur] that is fit to be eaten. Now, since the dough is not fit to be eaten [unless in a pressing situation] it is not considered Chametz at all. [Admur ibid]
 The reason: The reason it is forbidden to even be owned, is because one may come to forget and eat it on Pesach, being that it is still edible in a pressing situation. [Admur ibid; M”A ibid]