There
are different interpretations of the religious laws, but in general they do not
allow wheat or other traditional grains, including grain alcohol, during Passover with one exception:
Wheat flour that is used to
make matzos has been specially supervised from harvest through processing to
ensure that it has not had an opportunity to start fermenting, so it is
continually inspected to ensure that it is not in contact with moisture in order
to inhibit fermentation. The water used to make matzos is left out overnight to
cool, also in order to inhibit fermentation. Milling, mixing with water,
kneading, and baking are done in separate areas to avoid cross-contamination.
Fermentation is believed to occur about 18 minutes after a grain is mixed with
moisture, so after mixing the flour with water, kosher for Passover matzos are
put in the oven within that time limit; the ovens are separate from the
preparation areas so that the heat is not promoting fermentation of materials
being mixed/prepared.
Grain-based fermentation
products such as alcohol are also forbidden in kosher for Passover products,
since the purpose is to avoid using aged or fermented materials to mimic the
plight of fleeing slaves who didn't have time to let (sourdough) bread rise in
their hurry to flee Egypt.
(While it is quite likely that the newly freed slaves
would have grabbed already-baked bread, this specific
kosher for Passover practice of removing all leavened bread and other forbidden items from a household during the holiday is evidently intended as a ritual to evoke sympathy for their hurried exodus
during the Passover Seders practiced by their descendants.)
The traditional grains banned unless following the same rules as the matzo wheat include wheat, rye, barley, oats, and spelt; all of which were available in Egypt some 3,500 years ago.
Wine is allowed for Passover when the yeast is the product of the grapes themselves. But the wine must not include added non-kosher yeasts, other non-kosher additives (isinglass), or be produced/stored in a room containing grains or products made from grains. The work must also stop on the Sabbath, so observant Jews must be the winemakers.