One who wishes to make an eruv by placing food must set aside two meals’ worth of food. If bread is used, it must amount to the volume of six eggs, which is approximately 300 ml. (Others maintain that it must amount to the volume of eight eggs.) If one wishes to use food that is eaten together with bread, it is sufficient to use the amount of that food that would normally be spread on or eaten together with six eggs’ volume of bread (SA 409:7). If the eruv is meant to serve several people, two meals’ worth of food must be left for each person. If a large number of people are involved and one would like to minimize the bulkiness of the eruv, he may use olive oil, chocolate spread, or peanut butter, as relatively small quantities of these foods are used with a large amount of bread. One may also use a revi’it (75 ml) of vinegar, which is enough to use as a dip or dressing for two meals’ worth of vegetables (MB 386:35; 409:36). Drinks may also be used for the eruv as long as there are two revi’iyot (150 ml) per person (SA 386:6). Salt and water may not be used for the eruv (Eruvin 26a).
The food must belong to the person who plans to make use of the eruv, as he uses this food to establish his mekom shevita. When the eruv is meant for several people, the food’s owner must arrange for each person to acquire some of the food, making all of them partners in it. This is accomplished by means of third person, who lifts up the food with the intent to acquire it on behalf of all those who need to use the eruv (SA 413:1).
If the food set aside for the eruv was eaten before bein ha-shmashot, the eruv is ineffective. However, after bein ha-shmashot the eruv may be eaten, because once one has established his mekom shevita during bein ha-shmashot, it remains in effect for all of Shabbat (Rema 394:2). If the eruv was left in a place where it could not be accessed during bein ha-shmashot without transgressing a Torah law (for example, if a boulder would need to be rolled away to retrieve it), the eruv is ineffective (SA 394:3; 409:3-4).
When setting aside the eruv, one should recite the following berakha: “Blessed are You, Lord our God, King of the universe, Who sanctified us with His mitzvot and commanded us regarding the mitzva of eruv” (“asher kideshanu be-mitzvotav ve-tzivanu al mitzvat eruv”). One should follow this with the declaration: “With this eruv it shall be permitted to me to walk 2,000 amot from this place in every direction.” Bedi’avad, even if he simply said: “This shall be an eruv,” it is effective. But if he said nothing at all, he has not established an eruv (SA 415:4; MB ad loc. 15).
When the eruv is meant to serve several people, their names should be explicitly mentioned as part of the declaration. One must also take care that the eruv contains two meals’ worth of food for each person who needs to rely on it (SA 415:4). If he would like the eruv to be effective for multiple Shabbatot, he should add at the end of the declaration the phrase “for all Shabbatot of the year.” Then, as long as the eruv remains in existence, it is effective (MB ad loc. 16).
An eruv may be placed by a shali’aĥ (emissary or proxy). However, a minor, a non-Jew, or one who does not believe in the mitzva of eruv cannot serve as a shali’aĥ. The shali’aĥ must recite the berakha and the declaration. If he said nothing, the eruv is not effective (SA 409:8). However, it is effective if the owner of the eruv declares: “With the eruv that my shali’aĥ is setting aside, I will be permitted to walk 2,000 amot from the eruv in every direction” (BHL s.v. “ve-yomar”).
One cannot place an eruv on behalf of another without the other person’s knowledge. One may place an eruv for his minor children, and the teĥum that it establishes is binding for them. Similarly, one may place an eruv for members of his household who are over the age of bar or bat mitzva. However, if upon hearing that there is an eruv teĥumin they object and state that they do not want it, the teĥum that it establishes is not binding for them. A child who is under the age of six is considered secondary to his mother, so an eruv that is effective for the mother is effective for her child as well (SA 414:1-2).