Siman - Eruvin Daf 29
The majority of this Daf deals with identifying which foods can be used for an eruv, and the specific amounts required.
- Peaches vs. apples for making an eruv
Rav Nachman ruled that the minimum amount of apples required for an eruv is a kav, the amount sufficient for two meals. The Gemara challenges this ruling based on a ruling said in the name of Rav that five peaches is sufficient to make an eruv. Since apples and peaches are both fruits, why does Rav Nachman require the larger amount of a kav for apples?
The Gemara answers, הני חשיבי, the peaches are a significant food for the meal. Rashi explains, based on a Gemara later on that for those foods which are eaten as part of the meal the full equivalency of two meals is not required. Rather, only the amount of that food which would be eaten during the two meals need to be placed in the eruv. הני לא חשיבי – The apples are not significant, and the larger amount is required. The mefarshim mention that the apples in Talmudic times were hard and not tasty.
- Combining multiple foods to equal the amount of two meals
It stated in a Mishnah mentioned earlier, ובמזון שתי סעודות לעירוב – And all foods combine to equal the amount of food for two meals, which is the amount required to make an eruv. Rav Yosef thought to say, עד דאיכה סעודה מהאי וסעודה מהאי – that different foods may be combined only if there is an amount sufficient from this food for one meal, and one meal from this food; but that smaller amounts of three or more foods may not be combined. Rabbah said to him: אפילו למחצה לשליש ולרביע - Even a half, third or quarter of a meal may come from each of the foods. The only condition is that the combined total equals the amount of two meals.
- Making an eruv with beer
Rav Acha brei d’Rav Yosef thought to say before his father, Rav Yosef, that the amount of beer required to make an eruv is two quarters of a kav, or two lugin. This was based on a calculation made from Hilchos Shabbos regarding carrying, where the amount of beer one would be chayav for carrying is a quarter of a kav, which is four times the amount of wine one would be chayav for carrying. Assuming this ratio of 4:1 is a standard, then if half a lug of wine is needed to make an eruv, then two lugin of beer should be required.
The Gemara says this equation does not work since the reason we need four times the amount of beer than wine for carrying is that we need something חשוב, whereas with regards to an eruv we do not require an amount that is חשוב. We only require an amount that people would normally eat which in the case of beer is less than two lugin.
