787. A Folded-Over Matzah

110:12 The baker must be very careful to ensure that no matzah is folded over, nor that any matzah touches any other. This is because the place where they touch or where it is folded over doesn't bake quickly and may leaven. If a matzah did fold over, or if it inflated, that part must be broken off but the rest is permitted. However, if matzos touched in the oven while they were still moist, they are still permitted after the fact. An inflated matzah is one where the matzah divided at a thick part, forming a hollow the width of a thumb.

110:13 One must be careful not to take the matzah out of the oven before it's thoroughly baked (even with the intention to immediately return it to the oven – Mishnah Brurah 461:16). Underbaked means that if one broke it, strands of dough would be drawn out. Before this point, it's still like dough and will quickly leaven when taken out of the oven. The paddle used to remove it from the oven may no longer be used for matzah. If it's impossible to know whether or not strands of dough would drawn from it, one should act stringently out of doubt. If the outer surface crusted over, one may act leniently.