What’s the Truth about . . . Boiling Three Eggs?

Misconception: When making hard-boiled eggs, there is a halachic requirement to boil at least three eggs at a time, so that if a blood spot is found in one of them, it will be nullified by the others, and the other eggs and the pot will remain halachically permissible to use.1

Fact: There is such a tradition, but it is not mentioned in the Shulchan Aruch or other classic halachic sources.

Background: Cracking eggs and checking for blood spots is a hallmark of a Jewish kitchen. The Kitzur Shulchan Aruch (46:1) succinctly summarizes the reason for this: “Blood found in eggs is prohibited and sometimes the whole egg is prohibited, and therefore, when making a dish with eggs, they should be checked.” But as will be seen, it is not actually so straightforward. 

In multiple places, the Torah warns against eating blood, with the actual prohibition derived from Vayikra 7:26: “Do not eat any blood, from an animal or a bird, wherever you live.” The Gemara (Keritot 21a) concludes that this does not include blood inside an egg. There is a debate as to which blood the Gemara is referring to when it says that egg blood is permitted, as there are two potential sources of blood in eggs, as will be explained.

The Making of an Egg

The fowl egg begins its journey in the ovary of the hen, where there is a cluster of developing ova or yolks. Once a yolk is fully developed—and this happens almost daily in modern layers (hens that are raised to lay eggs)—ovulation takes place,2 whereby the yolk is released from the ovary into the oviduct, a meter-long, convoluted tube made up of five sections, initiating an approximately twenty-five-hour-long process in which the albumen (egg white), shell membranes and shell are added and the egg is laid. It is in the first section of the oviduct, where the yolk spends a mere fifteen to eighteen minutes, that fertilization can occur. In a conveyor-belt-like system, the developing egg moves along, with the egg white added in after about three hours, then shell membranes are attached, and finally, in a twenty-plus-hour process, the shell is deposited around the egg, followed by the addition of a thin outer coating of mucus.

   For the microscopic ovum to mature requires a great deal of nutrients, which are supplied via blood vessels in a membrane that surrounds the developing ovum. When releasing the ovum during ovulation, the membrane ruptures along a non-vascular strip known as the stigma.

   This explains the two potential sources of blood in an egg. One possibility is if the egg was fertilized in the first section of the oviduct. Development of the embryo commences immediately and takes place over the next twenty-four hours. When the egg is laid, there are already hundreds of cells, all grouped in a small, whitish annulus on the surface of the yolk. The development process is put on hold until the egg is incubated, either naturally under a hen or artificially in an incubator. Incubation provides heat and oxygen, and soon after incubation begins, blood islands appear, which are the precursors of the vascular system. Thus, in a fertilized egg that was incubated for at least a day after being laid, blood may be the start of the circulation system in a developing chick. 

   A second possibility for the source of blood in an egg is if the rupture of the vascular membrane during ovulation did not occur precisely along the stigma and a blood vessel broke and leaked some blood onto the yolk. When the rest of the components of the egg are laid on top of the yolk, this blood remains inside the egg. That is the source of blood in unfertilized eggs and in fertilized eggs that were never incubated.

   Because the blood is either from a developing chick or from a bad break at ovulation, it makes sense that blood spots are usually found on or near the yolk, the location where the embryo develops and the place where a broken vessel would leave blood. In a less common scenario, a blood vessel in the wall of the oviduct can rupture, resulting in blood in the albumen.

Egg Blood in Today’s Eggs

Halachic literature is replete with discussions of finding blood in hard-boiled eggs. Yet, in my experience (and I suspect in others’ as well), while I have seen blood spots in raw eggs, I do not recall seeing blood in a hard-boiled egg. The reason for this, I discovered, is because all commercial eggs today are candled and any egg with a large amount of blood is discarded (so as not to turn off consumers!). Thus, any egg reaching supermarket shelves in the Western world has, at most, small blood spots, which when hard-boiled are barely noticeable. This was not the case a few generations ago. To simulate what our grandparents experienced, Dr. Elyakum Berman, a veterinarian formerly in charge of Israeli egg-layers with whom I consulted for this article, procured eggs that were slated for disposal from a large Israeli egg-sorting facility. We opened some raw ones and found large amounts of blood—larger than a “blood spot” that we might find in our supermarket eggs. We then hard-boiled some and lo and behold, in many of them we saw easily discernable, large amounts of blood, probably similar to what our ancestors had seen. Prior to the commercialization of eggs, blood was found in eggs more frequently and in larger quantities; this occurred in hard-boiled eggs as well. 

   Returning to the statement in Keritot that the prohibition against blood does not include egg blood, and contrasting it with Chullin 64a that prohibits some egg blood, there are multiple opinions regarding how to understand the two statements (Beit Yosef, YD 66; Aruch HaShulchan, YD 66:6-16). 

   One explanation (Tosafot, Chullin 64b, s.v. v’hu, first option) is that blood found in an egg is Biblically permitted, even if it was from a developing chick, but the rabbis prohibited blood from a developing chick. The rabbis also forbade blood from an unfertilized egg but only because of marit ayin (and thus some Rishonim even ruled that the blood is permitted in some instances—see Tur, YD 66). Another position is (Tur, YD 66) that blood of a developing chick is Biblically prohibited, while blood in an unfertilized egg is rabbinically forbidden. The Shulchan Aruch (YD 66:2–3) seems to rule like this, stating that if the blood is found on the yolk, indicating it is the beginning of embryo development, then the entire egg is prohibited; if a blood spot is found in the albumen, indicating it is an unfertilized egg, the blood needs to be removed and the egg is permitted. The Pri Megadim (Siftei Da’at 66:14) rules that in an unfertilized egg, irrespective of where the blood is found, the blood is rabbinically prohibited and must be removed and the rest of the egg is permitted. 

   Due to the multiplicity of opinions regarding how to determine the origin of the blood based on its location within the egg, the Rema (YD 66:3) says that the custom is to prohibit any egg in which blood is found. However, if it is known that the egg is unfertilized, the blood spot is removed and the rest of the egg may be eaten (Shulchan Aruch, YD 66:7 with Shach 14).3

   In most of the Western world today, commercial layers are isolated from roosters, and thus the chance of purchasing a fertilized egg is miniscule (unless stated otherwise on the packaging). Furthermore, even if an egg were to be fertilized, it would likely not be incubated after being laid, as the eggs are collected daily. The possibility that the blood found in an egg is from a developing chick is therefore close to zero.

   In light of this reality, Rabbi Moshe Feinstein (Iggerot Moshe, YD 1:36, repeated in OC 3:61), writing in 1957, acknowledges that the overwhelming majority of eggs are not fertilized, but because a small minority are, and because throwing out an egg is not a significant loss for most people, it is proper to throw out any egg in which blood is found, even though that is technically not required by halachah.4 Despite this stringency, if an egg with blood was cooked with another egg, even a smaller one, or alone in a pot, it does not prohibit anything else. Rabbi Ovadia Yosef (Yabia Omer 3:YD 2; Yechaveh Da’at 3:57), agrees with that general conclusion,5 but observes that in Israel eggs are more expensive; the egg may therefore be eaten after the blood is removed.

   Historically, blood was found in only a minority of eggs, and today this is even more so due to candling.6 Thus, one may eat a roasted egg even though it cannot be checked (YD 66:8). There is no absolute obligation to check an egg before using it, but the custom is that if there is sufficient light, one should check an egg before cooking (Rema, YD 66:8), and it is an age-old practice to check eggs (Tosafot, Beitzah 16b, s.v. ka mashma lan; Beit Yosef:YD 66).7 Post facto, if blood was found after an egg was mixed with other eggs, the blood should be thrown out with as much of the egg as possible, and if the egg was already cooked, Rabbi Feinstein would not use the pot for twenty-four hours (Iggerot Moshe, OC 3:61).

Eggs Boiled Together

What happens when eggs are cooked together? The Gemara (Chullin 64b) says that a kosher egg boiled together with an egg from a non-kosher bird does not become non-kosher if they are both in their shells. At face value this seems perplexing since the egg shell is naturally porous (to allow carbon dioxide and moisture to be released and replaced by atmospheric gases, including oxygen, during the chick’s development). This is demonstrable by noting that an egg cooked in cholent looks and tastes like cholent. Yet the Shulchan Aruch (YD 86:5) rules like this. But the Shulchan Aruch also rules that an egg with a developing chick or even a blood spot would prohibit another egg that was cooked with it. What is the difference? The explanation is that the plain non-kosher egg has a weak taste, called “maya d’bei’a b’alma” (mere egg fluid), while the developing embryo, or the blood, has a real taste that is transmittable and can be absorbed from the “bloody egg” to the kosher egg or to the pot.8 To nullify an egg that is non-kosher because of blood from a developing chick, sixty-one other eggs would be required (YD 98:7). The need for sixty-one eggs is only if it is certain that the blood is from a fertilized egg; if the source of the blood is uncertain, then it does not prohibit the other eggs boiled together with it (Shach 86:17). 

   Because eggs cannot be checked before being hard-boiled, and because of the concern that cooking one or two eggs at a time might lead to the other egg and the pot becoming prohibited should blood later be found in one of the eggs, various customs developed. Some people have a separate pot just for eggs. Others always cook three or more eggs at a time so that a problematic egg will be nullified by the others. These practices are not mentioned in the Shulchan Aruch or other traditional sources, and thus seem to be either unnecessary or a later innovation, or both. The practice of cooking three or more eggs at a time is mentioned by Rabbi Moshe Sternbuch (Teshuvot V’hanhagot 2:YD 384), who says that those who cook three eggs should remove them only after pouring cold water on them so that they can’t prohibit each other when they touch and are still hot.9

   The mechanism by which boiling three eggs together helps is not at all clear.10 After all, while a majority (rov) can sometimes nullify an intermingled dry mixture of similar items (Shulchan Aruch, YD 109:1), in a liquid medium, the volume of kosher ingredients needs to be sixty times the volume of forbidden ingredients (Shulchan Aruch, YD 109:2). Various explanations are offered for why boiling at least three eggs together helps, but the accepted halachah is that it is not required to boil three eggs together and despite the reasoning being uncertain, if multiple eggs are boiled together and some are then found to contain blood, the eggs without blood are permitted to be eaten.11

  Because of the concern that when boiling many eggs together, some would have blood, various communities came up with other solutions. The Ben Ish Chai (year 2: Behar-Bechukotai:12) reports that in Baghdad they would add some ashes to the water, which technically “spoils” any taste and thereby prevents the taste of the potential bloodied egg from making the kosher eggs prohibited. 

   The health benefits of eggs were recognized by Chazal. The Gemara (Berachot 44b) records that Rav Yanai said in the name of Rebbi that for its size, a [boiled] egg is the healthiest food, except for meat. The Gemara then extols the benefits of lightly roasted eggs and fully roasted eggs. 

   Although we have greater access to eggs and observing the kashrut laws related to eggs has never been easier,12 for millennia Jews have been enjoying the health benefits of eggs while ensuring they meet halachic standards. Eggs are often associated with mourning and are served to mourners at the seudat havra’ah because they are round and represent the cycle of life. But they also symbolize rebirth. Rabbi Yaakov of Izhbitz (Seder Haggadah shel Pesach im Sefer HaZemanim, 5770, p. 109) explains that the custom to eat an egg at the Seder is because an egg appears to be a complete creation, when in reality it is the preparatory stage for a new life. The Exodus from Egypt—while appearing to be a full redemption—was merely the preparation for the future redemption. May it be speedily in our day. 


1. Special thanks to Dr. Elyakum Berman, a veterinarian, for educating me about eggs and reviewing the material in this article.

2. Hens ovulate whether a rooster is present or not. Roosters do not stimulate hens to produce more eggs. The increased egg production seen today is accomplished by selective breeding and clever manipulation of the timing of lighting in the hen house, not by feeding or injecting hormones (synthetic or natural) into hens. 

3. Rabbi Yosef Kapach’s interpretation of Rambam on this topic (Ma’achalot Asurot 3:7 [10], 6:4 [8]) is that the  location of the blood is unrelated to fertilized versus unfertilized, egg blood is a Biblical prohibition, and modern farming techniques do not impact the halachah.

4. He explained that because this is a legitimate chumrah, it is not bal tashchit (Mesoret Moshe [5773], p. 213).

5. Mishneh Halachot 4:96 agrees as well, but is concerned that people may not understand this new leniency. Rabbi Moshe Sternbuch (Teshuvot V’hanhagot 2:YD 384) says that in reality the eggs are permitted, but the custom is to be strict and he thinks that is correct and that one should not deviate.

6. In addition to blood, there are other “impurities” that can be found in eggs. Protein spots are clumps of protein found in the albumen. Rabbi Yisroel Belsky, zt”l, who served as OU senior halachic consultant, felt they are permitted but was uncertain if they are included in the custom mentioned by the Rema to remove blood spots, while yibadel l’chaim, Rabbi Hershel Schachter, OU senior halachic consultant, agreed but thought the custom is to remove them (OU document I-184). Meat spots form when small pieces of the wall of the oviduct are sloughed off as the developing egg is passing through. Rabbi Belsky felt they are prohibited as basar min hachai. Rabbi Moshe Feinstein (Iggerot Moshe, OC:3:61) raised the concern that the spots may actually be meat from a developing chicken, but concludes that they just look like meat but are actually “farbakkene ey—premature egg” and are permitted. Note that most scientists consider meat spots and protein spots to both be tissue sloughed off from the oviduct. While it may seem strange that meat spots should be permitted, it actually makes sense. Blood from a ruptured vessel would have been Biblically prohibited while in the hen, and the developing yolk would be basar min hachai if taken straight from the ovary, but both become permitted when naturally encapsulated in the egg. Thus, it is reasonable that the sloughed-off meat that would be basar min hachai if taken directly from the oviduct is kosher within the finished egg.

7. Rabbi Yisroel Dovid Harfenes (Vayevarech Dovid 1:YD 92) shows that based on fundamental principles, there is no obligation to inspect eggs for blood today, and that if it is very inconvenient, such as in bakeries or restaurants, it does not have to be done. He notes that when buying in a farmers’ market or non-Western country, the halachah may be different. 

Rabbi Yosef Molcho (d. 1768; Shulchan Gavoha, YD 66:21) quotes an amazing report from the Knesset HaGedolah that there are people who checked eggs for blood before hard boiling them by making a small crack in the shell, emptying the contents into a bowl, checking, reinserting the liquid into the egg, closing the opening and hard-boiling. Rav Molcho views this practice as strange.

8.  It is because of this porousness that an egg boiled in a non-kosher pot, e.g. a hard-boiled egg in a non-kosher restaurant, is problematic. That is in addition to the prohibition of bishul akum (YD 113:14).

9.  Rabbi Shlomo Kluger (HaElef Lecha Shlomo, YD 121) does not mention the custom of cooking three or more eggs, but comments that if eggs were boiled together and were removed when hot with a spoon, or the water was spilled out when hot and blood was found in one, the spoon and all the eggs are prohibited. Rather, he says, the water should be left to cool or cold water should be spilled into the pot. Maharsham (1:212) disagrees and says even if the eggs were removed individually when hot, the pot and other eggs remain permitted.

10. The case of multiple uncooked eggs in a bowl or eggs mixed with other ingredients and then blood is found in one—discussed in SA, YD 66:4 and elsewhere—is more complicated and will not be discussed here.

11. For a discussion of the halachic justification, see Taz, YD 66:5; Darkei Teshuvah, YD 66:40; Yad Yehudah 66:7. The Shach says even if just two eggs are boiled, the clean one remains permitted, and the Maharsham (1:137; Da’at Torah, YD 66:4) agrees with the Shach. Rabbi Shlomo Zalman Auerbach (Minchat Shlomo, Tinyana: 2–3:62) says that if one out of three eggs has a blood spot, the pot should not be used for twenty-four hours, and he is uncertain about the status of the rest of the food in the pot. But regarding the eggs, even if two out of three have blood, the other is permitted. Similarly, the Chazon Ish (YD Ta’arovot 26:2) says that third egg is kosher even if two eggs have blood, but the pot needs to be kashered. Rabbi Asher Zvi Lunzer (Ma’adanei Asher, YD 2:4) says that the Chazon Ish was discussing when the egg may have been fertilized. If it was definitely not fertilized, at most the pot needs to remain unused for twenty-four hours, but it certainly does not need to be kashered.

12. Due to both the isolation of hens from roosters and commercial candling.

Rabbi Dr. Ari Z. Zivotofsky is a professor of neuroscience at Bar-Ilan University in Israel.

This article was featured in the Summer 2024 issue of Jewish Action.
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