Nedarim 26

Onions.

Today’s daf concerns unintentional vows, one of four kinds of vows (along with vows of exhortation, vows of exaggeration, and vows that become impossible to fulfill) that a person can self-nullify. An unintentional vow is one in which the person makes a vow and discovers later that their intention when they made it was somehow flawed. Rav Adda cites an example: 

If one says: “It is forbidden for me to taste onions because onions are bad for the heart,” and others say to him: “But isn’t the kuferi onion good for the heart?”

Should the vow be nullified once it is discovered that it was made under the (wrong) assumption that all onions are bad for you? Or should it remain intact with a modification to exclude kuferi onions which, because they are good for one’s heart, do not align with the person’s original intention? These questions occupy the Gemara for much of today’s daf. Ultimately, Rabbi Akiva’s opinion that a vow that is partially dissolved is completely dissolved is determinative and so the vow in Rav Adda’s example (and a number of similar cases that are mentioned) would be nullified. 

As a lover of all things onion, the assertion that onions are bad for you caught my attention. This is not the first time that we’ve seen the Talmud make such a claim. On Eruvin 29 we learned:

A person should not eat onion because of the toxins in it. There was an incident with Rabbi Hanina who ate half an onion and half of its toxins and he fell deathly ill. His colleagues prayed for mercy for him and he survived. 

Twentieth century Talmud commentator Rabbi Adin Steinsaltz explains that onions contain a chemical compound (allyl propyl disulfide) which gives them their unique sharp flavor and is toxic when eaten in large quantities. In fact, he says, it can cause the death of particularly sensitive people (that is, if a cadre of rabbis does not intercede by praying on their behalf). The compound is volatile, which is why slicing onions releases some into the air, causing many peoples’ eyes to water. But it also quickly evaporates out of onions when they are cooked. The National Library of Medicine agrees that allyl propyl disulfide is an irritant, but it may be that Steinsaltz’s commentary is be a bit alarmist.

On Niddah 17, Rabbi Shimon ben Yohai suggests another potential danger in onions (as well as garlic and eggs). He says that one should not eat any of these items if they have been peeled and left to sit overnight. The Gemara explains why:

(Do not eat them) even if they are tied, sealed and placed in a basket for the night, as an evil spirit rests upon them. 

Evil spirits, it seems, like to roam at night and take up residence in onions, garlic and eggs that are not guarded by peels and shells. So, suggests Rabbi Shimon ben Yohai, one is strongly advised not to eat them the next morning.

The post-talmudic legal codes do not include Rabbi Shimon’s teaching, and so for most of the last millennium, presumably, Jews who enjoy meal prep have been bravely eating pre-peeled garlic and onions. But in recent times, coinciding with the emergence and popularity of studying Daf Yomi, some have given Rabbi Shimon’s view new life and suggested that eating cut up onions that have been left overnight should be prohibited by Jewish law. 

It’s not all bad news for onion lovers. On Pesachim 114, Rabba bar bar Hana quotes Rabbi Yohanan who cites Rabbi Yehuda, son of Elai, who opines:

Eat an onion (batzal) and sit in the shade (batzel), but do not eat geese and chickens, as your heart will pursue you. Devote less to your food and drink and spend more on your house.

This is a call to eat more simply. Drawing on the similarity between the word for onion (batzal) and the word for “in the shade” (batzel), Rabbi Yehuda has some advice for us: Better to invest your resources in your home, which will shelter you for a long time, than spend your money on fancy fattening food which provides only a short term benefit and, longterm, can cause “your heart to pursue you.” Sit in the shade and eat simple food, like onions. 

I recommend you sauté them first.

Read all of Nedarim 26 on Sefaria.

This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on November 20th, 2022. If you are interested in receiving the newsletter, sign up here.

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