Well, here's another tidbit that I know from my orthodox friend who gets real schmurah matzo each year and sometimes goes to bake it himself in Brooklyn. You don't have to add yeast to dough. If it sits out in the air for more than 18 minutes, yeast from the air starts to get into it naturally, so the bakers of the schmurah matzo have to get it into the oven within 18 minutes for it to be acceptable to eat during Passover