3) Various precautions are taken so that the flour and water (and the resultant dough) should not become warm, as this will speed up the fermentation process when they are mixed together.
One may not knead the matzah-dough nor form the matzos unless the house has a roof. One may also not work the dough nor form the matzos opposite an open window, even if the sun is not shining there. But if the windows are shut and they contain a pane of glaws, it is permitted, as long as the sun is not shining through the window… Similarly, they must be careful that the building where the matzos are being prepared should not be heated and warm.
4) As a rule, as long as the dough is being worked it does not become chametz. This paragraph discusses a limitation to that rule. One may not knead a piece of dough that is larger than the minimum amount subject to the requirement of ‘challah’*, and it is preferable to make it somewhat less. (Note: In that case, the separation of challah may become required later after a number of matzos are baked and gathered together in one place, whereby the minimum amount is amassed.) For our Sages, of blessed memory, calculated that if the dough is larger than the amount subject to the challah requirement, it is impossible to work the entire dough at one time, and part of it will be left without being worked. As a result, there is a concern that the dough not being worked will become chametz! [*The Torah requires that one remove a portion of a dough and give it to a kohein. This portion is called ‘challah’. The minimum-size dough that requires separating challah when being kneaded is one that containins 43.2 egg-volumes of flour. According to Chazon Ish, this may be as little as 2 lbs. 10.3 oz.]
6) After the flour is measured, it is put into the utensil into which water will be added and the dough will be kneaded. Regarding the utensil in which the kneading is done, one must make certain that it does not have any hole or crack in which a small amount of dough may remain and become chametz… One should take care after every eighteen minutes to clean out the utensil well and also wash his hands well…. (Note: Dough that has been sitting for 18 minutes without being worked is considered chametz.)
8-9) After the dough is kneaded, it is divided into separate pieces, each containing the amount of dough needed for an individual matzah, and a piece of dough is given to each person who rolls the dough… Those who roll the dough should roll it expeditiously, and they should not tarry in order to make the matzah into the shape of any form. They should take care that there should not be any crumbs from the dough on the board upon which the matzos are worked, and also that there should not be any dough stuck to their hands…
Who once said that Jews are rolling in dough – they’re right!
10) Once the dough is rolled out into the form of a matzah, it is ready to be passed to the baker for baking in the oven. First, however, the matzah is perforated with its distinctive holes, which help inhibit the rising of the dough. …One should be extremely careful not to pause with the matzah even mometarily at the opening of the oven, for there it hastens to become chametz due to the heat of the oven. Therefore, it is necessary to be extra particular that the one who passes the matzos to the baker be one who possesses Torah knowledge and is G-d-fearing so that he will be meticulous in this regard.
12) The baker should be very careful to make certain that no matzah should fold over, and that no matzah should touch the other. For in the place where they touch, and similarly in the place where the matzah is folded, it does not bake quickly, and becomes chametz. If it did occur that a matzah became folded or bloated, one must break off and discard that area of the matzah. This area alone is chametz and the rest of the matzah is permitted! (Ed. Great expertise is needed to examine and determine folds and bloating.)
QUESTION: In the matzah bakery, how long do you think the matzos are in the (very hot – approx. 1,000 degrees or more) oven? HINT: If you guessed 9 seconds, you’ve probably overestimated… (I’m serious)!
14) It is proper for every G-d-fearing person to personally attend and oversee the preparation and baking of his matzos, and to caution the workers to work expeditiously and carefully. This was the practice of the great sages of Israel, of earlier times, may their memory be blessed, and this is also the practice in our times. (Footnote #36: When working on the matzos, one should exert himself until he gets hot and sweats. This serves as atonement for one of the gravest of sins.) Ed. Most Jews today are not personally involved in the baking or supervision of their own matzos; relying, rather, on the many reputable matzah bakeries and their high-standards of halacha. However, in large Jewish centers, such as New York and Yerushalayim, many still follow this ancient practice. If you can visit a hand-matzah bakery, it is an experience of a lifetime.
Ibid. 113:8, pp. 162-3
Those who fulfill mitzvos in the most ideal manner bake the matzah to be used for the mitzvah on Erev Pesach after midday (!), since that is the time of the bringing of the Pesach-offering. However, since that is after the time when chametz becomes forbidden, it is proper before baking to explicitly nullify any bits of dough that may fall during the baking. (Footnote #43 on p. 138: “This practice is not followed in most communities.”)
Here are a few last relevant items from simanim 461 and 462:
(Excerpted from Halachos of Pesach, by Rav Shimon Eider z”l, pp. 18-19):
Egg matzos are usually baked from a dough in which fruit juice (e.g. apple cider) is used in place of water. Even if they would be kneaded only with eggs, they are considered in halacha like matzos kneaded with fruit juice. The Poskim say that the minhag is not to permit kneading matzos with fruit juice for Pesach. Even if it was kneaded and immediately baked, it may not be eaten on Pesach, but it may be held until after Pesach…. The Rama says that one should not deviate from the minhag except in case of great need – for a person who is ill or old and requires it. However, a healthy person may not eat egg matzos on Pesach!
‘Gebrukts’ (lit. broken pieces of matzah) (Excerpted from Halachos of Pesach, by Rav Shimon Eider z”l, pp. 51-52):
Where matzah in any form (e.g. matzah meal, cake meal – which are fully baked matzos ground up into different consistencies) came in contact with water (or other liquids), some communities have a minhag not to eat it on the first seven days of Pesach. We know that once matzah was baked it can’t become chametz again. What is the reason for this minhag? The ‘Keneses HaGedola’ says that it was made as a gezeira (Rabbinic restriction) that one shuld not, in error, come to use flour instead of matzah meal during Pesach. Another reason mentioned is that there is a possibility that some of the matzah flour was not kneaded well and when it will get wet it will become chametz. Since the last day of Pesach is ‘mid-rabanan’ (of Rabbinic law), many of those who accepted this minhag did not accept it for the last day of Pesach because of ‘Simchas (the joy of) Yom Tov’” (Ed. I don’t have this minhag, but I know people who do. Pesach menus for keepers of this minhag are greatly altered. In most of our communities, it is not the norm.)
I think we have covered most of the halachos related to matzah. Thank you, Hashem!