When Yom Tov precedes Shabbos:
Q. What is the reason for eruv tavshilin?
A. When the second or eighth day of yom tov falls on Shabbos (as the eighth day of yom tov does this year on April 23), or if Shabbos falls immediately after yom tov, it is rabbinically forbidden to cook or prepare on yom tov for Shabbos. When executed properly, eruv tavshilin allows us to prepare on yom tov for Shabbos.
Interestingly, there is no Torah prohibition to cook or bake on yom tov for Shabbos, even though ostensibly we may only cook on yom tov for yom tov itself. The Gemara (Pesachim 46b) offers two reasons why this does not constitute a Torah prohibition:
(a) Shabbos and yom tov are considered to be one unit, since the Torah refers to yom tov as Shabbos. Just as it is permitted to cook and bake on yom tov for yom tov, it is permitted to cook and bake on yom tov for Shabbos.
(b) When we cook or bake additional food on yom tov, it is not a Torah violation because it is possible that we will need the food for unexpected guests who might arrive on yom tov.
If the Torah permits the preparation of food on yom tov for Shabbos, why did the Rabbis institute the eruv tavshilin in the first place? The Gemara (Beitzah 15b) gives two explanations:
(a) When yom tov precedes Shabbos, we are prone to overlook the needs of Shabbos. The Rabbis therefore created a special, tangible preparation for Shabbos that must be attended to before the start of the yom tov, so people will remember to cook for Shabbos as well.
(b) If we were to permit cooking on yom tov for Shabbos without any reminder, we might not understand the reason, and think it is permissible to cook on yom tov for the subsequent weekdays as well; if done late in the afternoon this would violate a Torah prohibition.
Q. What is the procedure for eruv tavshilin?
A. On erev yom tov, Thursday April 21, set aside two types of food, one cooked and one baked (Mishnah Berurah 527:5–6). If you cannot obtain both items, a cooked item alone would be acceptable, but a baked item alone would not suffice. The cooked item must be at least the size of a large olive (k’zayit, approximately half the size of a chicken’s egg) and the baked item should be at least the size of a chicken’s egg (k’beitzah). Since not all cooked foods are eligible to be used for the eruv tavshilin, and the laws are complex, there is a common custom to cook an egg on erev yom tov specifically for use as the eruv tavshilin.
Hold the selected items while reciting the bracha and subsequent Aramaic text, as they appear in the siddur. You must understand the text as it is recited; if you do not understand the Aramaic text, recite it in your native language (Rama 527:12).
Q. When is the eruv tavshilin effective?
Can I eat the eruv tavshilin food? A. The eruv tavshilin allows us to prepare for Shabbos only on erev Shabbos, but not on a preceding yom tov day (Shulchan Aruch 527:13). In addition, every effort must be made to complete the preparations early enough on Friday afternoon so that the food will be edible well before Shabbos. Nevertheless, if the preparations were left until late Friday afternoon, they may still be done (Beiur Halacha 527:1).
The food items used for the eruv tavshilin must remain intact as long as preparations are being made for Shabbos. Perishable items used for the eruv tavshilin should be stored in the refrigerator as needed. If the eruv tavshilin foods were consumed or discarded, the eruv tavshilin ceases to be valid (OC 527:15).
Matzah is used on Pesach as the baked item of the eruv tavshilin. It is customary to use this matzah for an additional mitzvah as one of the two “loaves” of lechem mishnah at each of the three Shabbos meals, and to consume the matzah at the third meal of Shalosh Seudos.
Q. If a person is planning to be fully prepared for Shabbos before yom tov starts, is an eruv tavshilin still necessary?
A. Rav Moshe Feinstein zt”l understands the opinion of the Magen Avrohom (O.C. 527:1) to be that it is not absolutely necessary to make an eruv tavshilin if you are completely prepared for Shabbos. Nevertheless, Igros Moshe (Orach Chaim, 5:20:26) notes that even if you are not planning to cook or bake on yom tov for Shabbos, an eruv tavshilin should be performed as a precaution for an unexpected need. Rav Moshe z”tl in Orach Chaim, 5:37:9, writes that a bracha should not be recited in such a case.
Q. What should be done if I forgot to perform an eruv tavshilin?
A. If you forgot to perform an eruv tavshilin on Thursday, you may rely on the eruv tavshilin performed by the rabbi of the city, since it is customary for him to include his entire community in his eruv. We may rely on this only if the eruv tavshilin was not forgotten due to negligence (Shulchan Oruch ibid). In addition, we may rely on the rabbi’s eruv one time (MB 527:22). The Kaf Hachaim 527:48 suggests that this limitation of relying on the rabbi’s eruv only applies to consecutive yomim tovim. However, the Chayei Adam (Klal 102:7) questions whether we may rely on the rabbi’s communal eruv a second time, even if they were not consecutive times.
Another option is to have someone who made an eruv tavshilin cook for the one who forgot. In this case, ownership of the ingredients must be transferred to the one who made an eruv and is allowed to cook. This person may then proceed to cook even in the home of the person who did not make an eruv tavshilin (Shulchan Aruch OC 527:20).