Matza:
We are bidden to consume matza the first night of Pesach. The Torah recounts
that the people took unleavened dough with them out of Egypt, since they had no
time to prepare for the Exodus. More than a thousand years later the rabbinic
halachah mandated that from the time the water hit the flour the matza baker had
eighteen minutes to get the matza in the oven.
There are five different types of grain from which we may make matza for the
first night of Passover: wheat, oats, barley, rye and spelt. These five types of
grains are the types that become chametz if left in contact with water too long.
Matza and its ingredients are foods that have the ability to become chametz;
therefore we must cook and bake them with special care that they not become
chametz.
Chametz:
Chametz is leavened grain products. The Torah says that during the week of
Passover, "neither chametz (the result of grain that ferments) nor se'or (highly
fermented sourdough that is used to make another dough ferment) shall be visible
to you in all your boundaries." Se'or is the bread fermentation starter, such as
is used in sourdough bread today. Yeast is also a type of Se'or. Chametz is the
fermented bread product that se'or produces, if it is allowed to work long
enough.
The practical result of this is that all products that contain grains from one
of the five grains listed above may not be used for Passover food. No bread, no
pasta, no pancakes, no grain vinegar - unless the ingredients have been
specially supervised to make sure they have not fermented. Cider vinegar is
permitted, since it is not made from grain. All fruit and vegetables other than
these five grains are permitted. Margarine is questionable, since one does not
know its ingredients.
Kitneot:
Originally only five grains were considered potentially chametz: wheat,
barley, spelt, rye, and oats. For Jews of Ashkenazic origin post-talmudic
authorities added rice and legumes (kitneot) to this group. Legumes include
beans, peas and the seeds of any plant of the pea family. Later corn and corn
products were added to the kitneot family.
The Sephardic community did not accept this prohibition, because the main
articles of food in their diet were rice and legumes. Consequently, today
Sephardic Jews eat both legumes and rice on Passover, while Ashkenazic Jews do
not.