Kosher for Passover means avoiding fermentation of grains

 

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.