Is our Milk Kosher?
This article isn’t meant to be authoritative at all; it is merely a collection of the relevant sources.
Considering the reality that a number of dairy cows are considered taref, wounded in a serious way which chazal categorized, the question arises as to the kashrut of our milk. Firstly we’ll investigate the kashrut of a taref animal and then we’ll proceed to explain halacha deals with the production of milk nowadays.
An animal is considered taref if it has one of the 18 wounds listed by chazal and once it has such a wound, even if it can live more than 12 months it is considered taref. One possible issue that affects dairy cows is bloat, which is a form of indigestion due to accumulated gas and leads to the swelling of the rumen. It can usually be treated by a professional veterinarian or the farmer with a regular procedure without surgery, in which the rumen of the animal is punctured. If the animal’s rumen is punctured, it could be considered taref. Additionally, there can be other factors which make it common to have an animal that is taref, such as a lesion in the lungs, that can occur roughly 40% of the time for large cattle. With these two factors together, in theory, it could be that the instance of taref animals amongst dairy cows would be a majority. However, we assume that this isn’t the case and follow the general assumption made by the poskim that it is a statistic greater than 1/60 (or 1.67%) but less than 50%. Considering that the instance of taref depends on the treatment of the animals, location, and other factors, it is extremely difficult to figure out and isn’t well calculated. See Rav JD Bleich’s article regarding the statistics of taref in dairy cows. Nonetheless, for our purposes, the actual accurate statistic isn’t necessary critical as long as it is between 1.7% and 50%.
Let’s say we have a cow which is certainly taref, what’s the status of its milk? The Gemara Bechorot 6b derives from the pasuk that milk from a non-kosher animal is forbidden. The Mishna Chullin 116b similarly forbids the milk of a taref animal and this is codified by the Tur and Shulchan Aruch YD 81:1.
What about the milk of a cow we’re unsure of its status? The gemara Chullin 11a establishes that based on the concept of rov, we can rely on the fact that most animals are kosher to permit the meat of an animal. Nonetheless, rabbinically anything with an instance of a significant minority (potentially 10%) needs to be checked. Despite the general rabbinic obligation to check that an animal isn’t taref before eating its meat, this doesn’t apply to drinking its milk since it is impossible to check if it is taref while it is alive. Therefore, the Isur Veheter 49:1 states that we have a presumption that milk from an unchecked cow is kosher.
Furthermore, if we have a group of cows in which we know some are taref but they can’t be identified we can say that when we remove one animal that is considered to have common from the majority of kosher animals. This halachic principle is known as kol d’parish m’ruba parish, anything which departs from a mixture retains the status of the majority of that mixture. If so, each time an animal is separated from the herd to be milked, it is deemed kosher due to this principle and thereby its milk would be kosher. Rav Hershel Schachter explains that while it is true that both chazaka and kol d’parish m’ruba parish would suffice to permit the milk of of an individual cow, the statistical reality reveals that once the milk from multiple cows is mixed together there is a large incident of taref milk mixed into the general pool of milk. The basis for his argument is that chazaka and rov are only principles that guide halacha whenever a circumstance is unclear, however, they do not pretend to clarify the reality to conform to its principle and if the reality is shown to be otherwise we should follow the reality and not chazaka or rov. As long as the amount of non-kosher milk in the mixture is greater than 1.7% then the entire mixture becomes non-kosher. That is based on the fact that liquid mixtures of a similar type require 60 time of the kosher ingredient in order to nullify the non-kosher one. Effectively, according to Rav Schachter, the regular consumer milk, which is a production of mixing the milk from multiple cows, would be non-kosher. Additionally, note that Rav Schachter leaves his argument as a question and not a pesak.
On the other hand, Rav Asher Weiss (Minchat Asher Shemot siman 43) argues that principally we view each cow as kosher because of kol d’parish m’ruba parish and even when their milk is mixed up the milk from each cow retains its kosher status despite the overall statistic. His primary argument is that once we have a halachic principle to state that the milk is kosher the halacha ignores the physical reality or statistic. One proof for his argument can be derived from Gemara Zevachim 73b which implies that once the principle kol d’parish m’ruba parish is employed even if the items are later mixed up, the remain kosher. Another proof is the Rama who states that the cheese made from many unchecked cows who were only considered kosher by merit of a chazaka remains kosher. This gemara is cited by the Rosh (Chullin 7:37) for a similar point.
Another proof for this approach is from the Shulchan Aruch and Rama YD 81:2 who write that if you have a cow which is certainly taref and its milk was mixed up with the milk of 59 unchecked cows we say that the whole mixture is kosher since we presume that the milk of the taref animal is less than 1/60 in the whole mixture. It is also clear that we presume that the other 59 animals must be kosher otherwise their milk would be non-kosher making the volume of the non-kosher greater than 1/60. This is true even though we also have a concept that there’s a miyut hamatzuy of animals which have an adhesion on the lungs and render it taref. This seems to indicate that we view each cow individually and permit each one based on the majority even if all of their milk is mixed together afterwards. 
It is for these reasons and others that the overwhelming majority of rabbis consider commercial milk kosher.
- Chullin 42a, Rambam (Hilchot Shechitah 10:9)
- See this article by the University of Nebraska on the causes and treatment of bloat.
- See Har Tzvi YD 36 who writes that it would be considered safek taref and could be considered kosher if it lives more than 12 months. Regarding the consideration of the left displaced abomasum surgery, see Rabbi Menachem Genack’s article in Tradition where he permits the milk.
- Based on research, Tov Lev (p. 56) writes that it is impossible for the statistic to be less than 1/60.
- See Ramban Chullin 3b, Milchamot Chullin 3b, Gra YD 1:4. As to the definition of miyut hamatzuy see Mishkenot Yakov YD 17 and Ginat Egoz 16:5 no. 4.
- Pri Megadim (Siftei Daat 81:6)
- Zevachim 73a
- Rav JD Bleich writes that modern commercial milk is produced as a mixture of hundreds of cows. See also, Tov Lev (p. 57) who quotes the statistic that 45% of commercial milk comes from farms with 500 dairy cows or more.
- Tov Lev (Siman 5, p. 57) citing Rav Schachter. See Rabbi Zylberman’s article on yutorah regarding Rav Schachter’s opinion. Rav Gavriel Iliavitch (Kovetz Bet Aharon VeYisrael kislev 5763 p. 66-76, nissan 5763 p. 124-136) similarly feels that there is reason to question the kashrut of milk and at best leaves it as a question on the minhag.
- Rav Elchanan in Kovetz Biurim (Shev Shemaytata no. 4), Shaarei Yosher (Shaar 3 ch. 4 s.v. velechen)
- Shulchan Aruch YD 98:2 rules that a liquid mixture of similar types with both kosher and non-kosher ingredients, the entire mixture is kosher only if the volume of the kosher ingredients is 60 times the volume of the non-kosher ingredients. The Shulchan Aruch holds that this is only a rabbinic requirement in accordance with most rishonim, such as the Tosfot (Chullin 97a s.v. amar rava), Ran (Chullin 34b), Rosh (Avoda Zara 7:29), and Rambam (Maachalot Asurot 15:6), and Rashba (Torat Habayit 16a), unlike Rashi (Chullin 109a s.v. VeTu) who says there’s no nullification in mixtures of like types. See further on the Nullification page.
- Rav Bleich makes this argument based on Shulchan Aruch.
- Rav Zalman Nechemya Goldberg (Habear adar 5764 p. 78-83), Rav Moshe Heinemann (Mesorah journal adar 5765 p. 76-78), Rav Yisrael Belsky, Rav J. David Bleich, and Rav Baruch Simon.