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A number of laws and customs apply to the 14th of Nissan, the day before Passover. (Keep in mind that in Jewish tradition, every day starts the previous night. For example, if the first day of Passover is a Tuesday, the holiday starts with the Seder on Monday night, and Monday is the day before Passover, commonly referred to as Erev Pesaĥ).
The Sages prohibited eating matza on Erev Pesaĥ. This was both to ensure that everyone would look forward to eating it during the Seder, and to make a clear distinction between matza eaten before Passover (not mandatory) and matza eaten at the Seder (mandatory). However, cakes, cookies, and matza balls made with matza meal may be eaten on Erev Pesaĥ. In the last three hours before the holiday begins, it is proper to minimize eating so as to ensure a hearty appetite at the Seder.
On the night of the Exodus, the tenth plague killed off the firstborn Egyptians, while the firstborn Israelites were miraculously saved. Therefore, it is customary for firstborns to repent and fast on Erev Pesaĥ. Alternatively, they may eat if they participate in a siyum masekhet, a small celebration marking the completion of the study of a Talmudic tractate (or an important Torah book). This allows them to eat not only at the siyum, but for the rest of the day as well. Since eating at a siyum is a mitzva, it overrides the custom of fasting. When Passover starts on Friday night, the fast of the firstborns is moved up to Thursday (to avoid fasting on Friday).
What happens when Erev Pesaĥ is on Shabbat and the holiday starts with the Seder on Saturday night? Several practices change because of Shabbat. The search for ĥametz is performed with a berakha on the night of the 13th of Nissan, Thursday night, because searching for ĥametz and destroying it is forbidden on Shabbat. After the search, the ĥametz is nullified as in any other year. On Friday morning, it is burned or thrown away (except for the ĥametz to be eaten on Shabbat morning).
On Shabbat day, bread may still be eaten at lunch, but only until the time eating ĥametz becomes prohibited. (As we mentioned above in section 5, this is two hours before midday. The exact time can be found in standard Jewish calendars.) At the end of the meal, we brush our teeth well to get rid of any remnants of ĥametz. Any remaining ĥametz should be flushed down the toilet or put in a dumpster, after which we recite the second declaration of nullification. All this should be completed by the time benefiting from ĥametz becomes prohibited, i.e., an hour before midday.
The obligation to eat a third Shabbat meal (se’uda shlishit) may be fulfilled with meat, fish, fruit, or matza balls.
Some people prefer to dispose of all their ĥametz before Shabbat, and to have Shabbat meals with kosher for Passover food. Instead of beginning each meal with bread (26:22 above), they use fried matza. Even though eating matza on the day before Passover is prohibited, this is permitted because frying matza changes its taste.
