General Overview of Kashrut
- 1 General
- 2 Non-Kosher Animals
- 3 Non-Kosher Fish
- 4 Blood
- 5 Nevelah
- 6 Teriefah
- 7 Chelev
- 8 Gid HaNasheh
- 9 Ever Min HaChay
- 10 Tevel
- 11 Orlah
- 12 Chadash
- 13 Yayin Nesech
- 14 Fish and Meat
- 15 Fish and Dairy
- 16 Bishul Akum
- 17 Pat Akum
- 18 Chalav Yisrael
- 19 Kelayim
- 20 Meat and Milk
- 21 Veal
- 22 Sheretz
- 23 Honey
- 24 Sources
- It’s forbidden to eat any non-Kosher food of any size. 
- It’s forbidden to eat the taste of non-Kosher food which was absorbed into another food.
- It is permitted to smell food which is forbidden from benefit and certainly something non-kosher unless the food was prepared specifically for fragrance. 
- Non-Kosher animals are those which do not have completely split hooves and chew its cud. Examples of non-kosher animals include pig, camel, donkey, and horse. 
- The Torah specifies 24 non-Kosher birds and in practice we hold that any specifies about which we do not have a tradition that it is Kosher may not be eaten. 
- Eggs or milk of a non-Kosher animal is also non-Kosher. 
- Fish which has fins and scales are Kosher, while all others are non-Kosher.  Fish do not need ritual slaughtering. 
- Blood of any animal or bird is forbidden to be eaten. Therefore after a kosher animal is ritually slaughtered it must be salted properly in order to remove the blood. 
- Fish blood is permitted to drink, however, it’s forbidden if it’s gathered in a vessel unless it’s recognizably fish blood such as having in it fish scales. 
- Human blood which separated from the area which it left the body is forbidden, however, if one’s gums are bleeding it is permitted to swallow that blood. 
- If someone finds a blood spot in an egg today should be strict to throw it out.
- Any animal, kosher or not, may not be eaten unless it has first been ritually slaughtered properly, otherwise, the animal is considered Nevelah. An unwarranted pause, excessive pressure, or using a jagged knife are among the numerous defects of a ritual slaughtering which would cause the animal to be Nevelah. 
- An animal which has a health defect or disease which Chazal specify is considered Teriefah and is forbidden to eat. 
- Cows which have their stomachs punctured for gas build up might not be considered teref and as such the Shochet doesn't need to check for it, however, if he sees that it has scares from those punctures it isn't kosher.
Dairy Products of Non-kosher Animals
- The milk of a Tereifah animal is non-Kosher. 
- Certain fats of domestic animals (cattle, sheep, and goat) are forbidden, however, fat of birds or other kosher animals is permissible. Therefore after the ritual slaughtering, the butcher or other expert removes these forbidden fats. 
- Many poskim hold that it is permitted to use soaps made from animal fats even if they included the forbidden fats.
- It’s forbidden to eat the Gid HaNasheh which is the sciatic nerve in the hind thighs of kosher animals. 
Ever Min HaChay
- It’s forbidden to eat a limb that was detached from a live animal. 
- A fruit tree within its first three years is called Orlah and its fruit are forbidden to eat. 
- Any grain which took root after 16th of Nissan is forbidden to be eaten until the next 16th of Nissan. 
- There is considerable debate whether this applies outside Israel. 
See Kosher Wine: Yayin Nesech, Stam Yeinam, and Maga Akum for details.
- Wine which was poured in a sacrificial manner to an Avoda Zara is forbidden biblically. The same is true of any food served to an Avoda Zara. 
- Wine that was moved by a non-Jew is forbidden by rabbinic decree. There is a dispute whether the wine is forbidden upon touch of a non-Jew. 
- One may not drink wine that belongs to a non-Jew and is considered Stam Yainom. 
Fish and Meat
- It’s forbidden to eat fish and meat together because Chazal felt that there was a health concern. 
- A person who ate fish should wash out his mouth with a solid and liquid before eating meat. Ashkenazim hold that one doesn't have to wash one's hands but Sephardim hold that one should also wash one's hand before eating meat after having fish.
- It is permitted to cook fish in a meat pot even if it is was used within that same day.
- Fish in meat is nullified one in sixty even though it is a concern of danger.
- Some hold that it is permitted even initially to add more to the mixture in order to nullify the danger of meat and fish and that there would be sixty times.
Fish and Dairy
- There is a Sephardic custom not to eat fish and dairy together.  Such is the Syrian practice. Ashkenazim hold that it is permitted.
- Ashkenazim hold that it is permitted to have fish and dairy together.
- Even according to those who don't eat fish and milk together may have fish cooked with butter. 
- One may not eat bread that was baked by a non-Jew. see the Pat_Akum page
see the Kosher Milk page
- One may not mingle seeds of different species of plants however, if one did so the product is permitted. 
- It’s forbidden to sow a vegetable or grain near a grape vine and if one did so the product is forbidden. 
Meat and Milk
- Even though both meat and milk separately are Kosher, when mixed they are forbidden. Any cooked combination is biblically forbidden.  Rabbinically, a combination of milk and meat of non-domesticated animals or milk and poultry is forbidden. 
- Many poskim hold that it is permissible to own stock in a company that sells meat and milk cooked together such as McDonald's.
Many poskim permit eating veal with a reliable hechsher. The issues involved are that there is a greater percentage of terefot, the animals aren't treated nicely, and the diet consists of meat and milk.
- The fact that there is a higher percent of terefot doesn't exclude the ability of a shochet to check the lungs to determine if it is kosher. The kashrut organizations checked that there isn't a higher concern of a teref developing in the intestines of the calf when raised as veal.
- Regarding the fact that the animals aren't treated nicely, that doesn't render the meat non-kosher. 
- Since the calves are fattened with a meat and milk formula there is an issue of eating an animal that was fattened with something that's forbidden in benefit (nitfatma biusrei hanah). There are several factors to permit the meat nonetheless. First, not all rishonim agree that the halacha forbids an animal that was fattened with something that's forbidden to benefit from. Second, since the meat is non-kosher some rishonim hold that the meat and milk combination is not forbidden to benefit from. Third, perhaps the diet of the veal is comprised of other permitted ingredients and the forbidden benefit is only considered one factor but not the sole contributor (zeh vzeh gorem). Forth, the meat and milk were individually cooked before being cooked together in which case it might not be considered a meat and milk combination that is forbidden to benefit from. The kashrut organizations have tried to mitigate this issue by using a kli sheni to create the formula and not kli rishon, which would also not create a meat and milk combination that is forbidden.
- See this topic discussed on OU.org and in the Journal of Contemporary Halacha.
- All insects are forbidden to eat except a certain species of locust which is unknown to us and as such one shouldn’t eat locust. 
- Bees' honey is kosher, because the honey is not is not an actual secretion of the bee. Rather, the bee functions only as a carrier. 
- Although some poskim argued that royal jelly should be considered kosher, most poskim hold that it is not kosher.
- Rambam Machalot Assurot 14:2
- Shulchan Aruch Y.D. 98:1
- The Gemara Avoda Zara 66b discusses whether a smell ('reyacha') is halachically significant. The Rashba Teshuva 3:234 writes that for anything that isn't made to give off a smell even if it is forbidden for benefit such as Orlah or Kilayim it is permitted to smell. Tosfot Avoda Zara 12b s.v. elah disagrees. Shulchan Aruch Y.D. 108:6 rules like the Rashba, while Shach 108:27 sides with the Tosfot. Rabbi Shmuel Pinchasi on dailyhalacha.com follows Shulchan Aruch. See Or Tzadikim 12:59 who writes that one shouldn't smell non-kosher food since one might come to eat it.
- Vayikra 11:3-8, Rambam Machalot Asurot 2:1, S”A YD 79:1, The Laws of Kashrus (Rabbi Binyamin Forst; pg 33-4)
- Vayikra 11:13-20, S”A YD 82:2
- The Laws of Kashrus (Rabbi Binyamin Forst; pg 35-6)
- The Laws of Kashrus (Rabbi Binyamin Forst; pg 35) quoting Darkei Teshuva 82:26
- Gemara Bechorot 5b-6a, Rambam Machalot Asurot 3:1, S”A YD 81:1, The Laws of Kashrus (Rabbi Binyamin Forst; pg 33-4)
- Vayikra 11:12, S”A YD 83:1
- S”A YD 13:1
- Vayikra 7:26-27, Devarim 12:23, Rambam Machalot Assurot 6:10, S”A YD 66:1
- S”A YD 66:9
- The gemara Keritut 21b says that eating human blood is only derabbanan once it separated from the body. The gemara explains that if a person is eating and finds blood on the piece of food that is forbidden, however, if a person’s teeth are bleeding that blood is permitted and a person can swallow it. Rambam (Machalot Asurot 6:2) and Shulchan Aruch YD 66:10 codify this halacha. Rama YD 66:10 adds that if human blood fell into a food and isn't recognizable it doesn't forbid the mixture. The Pri Megadim S"D 66:16 writes that theoretically this is the case even if the human blood is in the majority.
- Igrot Moshe OC 3:61 writes that although the majority aren't fertilized at all and there is no issue so the blood could be removed and the rest eaten but since eggs are so cheap it is right ot be strict and throw it all out.
- S”A YD 18:1, 23:1-2, 24:1
- The Mishna Chullin 42a enumerate 18 defects and the Rambam Hilchot Shechitah 10:9 counts 70.
- Rav Shlomo Amar in Shema Shlomo YD 7:1 5772 p. 77
- Based on Mishna Chullin 116b, Rif Chullin 19a, Rambam Machalot Asurot 3:10, Rosh Chullin 3:52, Shulchan Aruch YD 81:1
- Shulchan Aruch YD 64:1
- Rav Ovadia Yosef (Taharat Habayit v. 3 p. 244) quotes the Tosfot niddah 32a and many other rishonim that smearing forbidden animal fat on one's skin isn't forbidden because it is like eating. Additionally, he quotes the Pri Chadash YD 177:4 who says that the soaps are unfit for eating and as such there's no issue of using soaps. The Aruch Hashulchan YD 117:29 agrees. See however, Biur Halacha s.v. 326:10.
- Beresheet 32:33, Rambam 8:1, S”A YD 64:11
- Beresheet 9:4, Rambam Machalot Assurot 5:1, S”A YD 62
- Rambam Machalot Assurot 10:19
- Vayikra 19:23, Rambam Machalot Assurot 10:1, Sefer Hachinuch (Mitzvah 247)
- S”A OC 489:10
- Beiur Halacha 489:10 s.v. Af
- Rambam Machalot Assurot 11:1
- S”A YD 124:11, Shach 124:20
- Rambam Machalot Assurot 11:7
- Shulchan Aruch YD 116:2, Yalkut Yosef YD 87:83, Kitzur Shulchan Aruch 33:1. See Dr. Fred Rosner's article in Tradition v. 35 pp. 36-44 about the theory that it is unhealthy since there's small bones in fish and a person might swallow one without realizing if he is also eating meat at the same time which doesn't have small bones. However, he questions that theory and concludes that we don't have a scientific explanation of this danger today.
- Shulchan Aruch YD 116:3 based on the practice of the Rosh that one should wash one's hands and mouth before eating meat after having fish. However, the Rama says that practice isn't to wash one's hands or mouth before having meat but it is proper to wash out one's mouth with a solid and liquid.
- The Magen Avraham 173:1 and Chatom Sofer YD 101 question whether this prohibition should really still apply today since it doesn't seem to be dangerous. Kaf Hachaim 173:9 says that since this is a question of health one should be strict.
- Yalkut Yosef YD 87:85 (Isur V'heter v. 3, p. 316), Rav Yitzchak Yosef (Motzei Shabbat Chukat 5779 min 30)
- Shach (Nekudat Hakesef YD 116:2) holds that fish in meat is nullified one in sixty. Taz 116::2 understands that the Maharil holds that it isn't nullified at all. Yabia Omer YD 1:7:10 quotes the Chatom Sofer 101, Rogachover in Safnat Paneach 264, Zer Zahav 39:7, Sheilat Shalom 2:165, Bet Shlomo 2:218, Olat Yitzchak 146, and Sh"t Maharitz Chiyitz 52 who agree with the Shach. Yabia Omer also agrees with the Shach.
- Pitchei Teshuva YD 116:3 writes that it is permitted to even initially nullify something that is a concern of danger. Yabia Omer YD 1:8:7 quotes Rav Yitzchak Elchanan in Ayin Yitzchak OC 24:2, Maharash Engel 1:83, Chamudei Doniel 96a, and Divrei Shalom Vemet OC 13 who agree. However, he also quotes the Tuv Taam Vdaat 3:2:10 and Anei Tzedek YD 49 who hold that it is forbidden to initially nullify something that is a concern of danger. Yabia Omer is lenient.
- Bet Yosef 87:3, Yalkut Yosef YD 87:84, Yechave Daat 6:48, BI"H, Beha'alotecha, 15, Kaf Hachaim 87:24, Horah Brurah 87:13. Rabbenu Bechay Shemot 23:19 explains that it is spiritually dangerous to eat fish and cheese because milk is derived from blood which causes the one who eats it to become cruel and when that mixes with fish which causes the one who eats it to become lazy together they are negative for a person's soul. He concludes that fish and cheese causes bad middot and tzarat. See Darkei Teshuva 116:43.
- Rabbi Mansour
- Shach YD 87:5
- Shach 87:5, Taz 87:3, Pitchei Teshuva 87:9
- Pitchei Teshuva 87:9 citing the Knesset Hagedola and Chinuch Bet Yehuda 61, Yalkut Yosef YD 87:85, Kaf Hachaim 87:24, Horah Brurah 87:13
- Shulchan Aruch YD 113:1
- Rambam Kelayim 1:1, 6:1, The Laws of Kashrus (Rabbi Binyamin Forst; pg 42)
- Rambam Kelayim 1:1, 6:1, The Laws of Kashrus (Rabbi Binyamin Forst; pg 42)
- Rambam Machalot Assurot 9:1
- Rambam Machalot Assurot 9:4
- Shulchan Aruch YD 117 writes that it is forbidden to sell non-kosher food. Gilyon Maharsha 117:1 forbids even investing in a non-kosher business even though there's no concern that one will come to eat the non-kosher food. Kaf Hachaim 117:69 quotes most achronim who are strict about investing in a non-kosher business but some who are lenient. Igrot Moshe EH 1:7 allows buying shares of a publically traded company that works on Shabbat since he doesn't mean to buy any share of the actual company and its tools but just to invest in the value of the corporation. He allows that as long as one isn't invested so heavily that he is involved in the voting or management. Similarly, Rav Dovid Feinstein (cited by Journal of Halacha and Contemporary Society v. 24 p. 85) ruled that it is permitted to own stock in McDonald's since one is just an investor and not like one is actually doing business with the non-kosher food. Halachically Speaking v. 4 Issue 21 p. 7 discusses this as well.
- Igrot Moshe EH 4:92 was strict that the intestines should be checked in calves raised for veal. Rav Aaron Tietelbaum is cited by the RJJ v. 45 p. 8 fnt. 5(by Rabbi Josh Flug and Rabbi Ezra Schwartz) that the kashrut organizations checked and didn't find a higher incident of a concern.
- Igrot Moshe EH 4:92
- Rama YD 60:1 based on Avoda Zara 49a. Kaf Hachaim 60:12 is strict.
- Piskei Tosfot Temurah n. 20 writes that an animal that suckled from a teref animal is permitted for consumption. Peleti 60:1 explains that the Piskei Tosfot hold that behema shnitfatma is permitted except for avoda zara which is forbidden to benefit from even in an abnormal way. However, that won't really help by veal since meat and milk is forbidden even in an abnormal way (RJJ article). Pri Chadash YD 60:5 is lenient after the fact to consume an animal that was fattened with food that is forbidden to benefit from since Rashi and Rambam are lenient. See Isur Vheter 47:9, Pri Megadim SD 60:5, Igrot Moshe OC 1:147, Tuv Taam Vdaat 2:236
- Dagul Mirvavah 87:1 based on Rambam Pirush Mishnayot Keritut 3:4
- RJJ article cites Mesorah v. 15 pp. 74-8 who suggests that it is zeh vzeh gorem because of the water that the calves drink. RJJ Article p. 17 clarifies that the kosher ingredients in the formula aren't considered zeh vzeh gorem because of chaticha naaseh nevelah. Pri Chadash 47:9 is lenient on any zeh vzeh gorem where the animal itself is considered a gorem together with the food, but his opinion is disputed by Kanfei Yonah YD 60. Also, Bet Hillel 60:1 based on Tosfot A"Z 48b s.v. vrabbanan writes that the animal isn't considered one of the factors as a gorem.
- Pri Megadim OC 673:1 writes that there's no bishul achar bishul of meat and milk if they were already cooked together but if they were cooked separately it is still forbidden to cook them together. Yalkut Yosef Isur Vheter v. 3 p. 190 writes that it is possible to question this.
- Pri Megadim SD 87:19 writes that cooking meat and milk together in a kli sheni isn't considered cooking and the result would be permitted to benefit from. Yalkut Yosef Isur Vheter v. 3 p. 111 agrees.
- Vayikra 11, The Laws of Kashrus (Rabbi Binyamin Forst; pg 38)
- Shulchan Aruch YD 84:8
- Sh”t Yechave Daat 6:47
- Bechorot 7b, Rambam Maachalot Asurot 3:3, S"A YD 81:8, Yalkut Yosef Isur VIheter Vol. 2 81:38 see also Star-K
- Rav Shlomo Zalman Auerbach (Minchat Shlomo Tinyana 64), Rav Hershel Schachter