Fall 2025

[This is an expanded version of the article that appeared in the Fall 2025 print issue of Kashrus Kurrents.]

Basar b’cholov – the Torah’s prohibition against mixtures of meat and milk and its Rabbinic guardrails – constitutes one of the most fundamental laws of kashrus. Repeated thrice in the Torah, the posuk of lo sevasheil g’di bachaleiv eemo[1] – do not cook a young goat in its mother’s milk – proscribes three distinct actions: (1) cooking meat with milk (bishul);[2] (2) eating the mixture (achilah); and (3) deriving benefit from the mixture (hana’ah).

Conventionally, milk is defined as the mammary gland secretion of a lactating mammal. This definition usually aligns with the halachic parameters of what’s considered milchig for purposes of keeping it separate from meat in a kosher kitchen. But is that always so? Can milk sometimes be pareve?[3]

Certainly, the whitish, liquid derivatives of beans and nuts – called “milk” using borrowed terminology – are pareve.[4] Resembling actual milk, plant-based milks may be subject to halachic restrictions due to maris ayin.[5]Moreover, they are commonly processed on equipment shared with dairy, which may compromise their pareve status.

But how about mammalian milks? Are they ever conferred a pareve designation?

Exegetical Expansions and Exceptions

Despite the reference in the posuk to a g’di, a young goat, Chazal determined that the prohibition encompasses the meat of all kosher beheimos – cattle, sheep and goats – regardless of age. Furthermore, despite the possessive form eemo – referencing the animal’s own mother – basar b’cholov precludes cooking meat in the milk of any kosher beheimah – and even in the animal’s own milk.[6]

Nevertheless, since the possessive eemo suggests a degree of equivalence between the sources of meat and milk, Chazal deem some cases of milk to be excluded from the prohibition, at least on a d’Oraysa level:

► Non-Kosher Animals – Milk from a non-kosher animal is not kosher – hayotzei min hatamei tamei. When non-kosher milk is cooked with kosher meat (e.g., camel milk and flanken) and imparts taste, the meat, too, becomes non-kosher due to absorption.

But does the mixture become basar b’cholov? The answer is no. Just as g’di by definition connotes a kosher animal, eemo – itsmother – likewise alludes to milk derived from a kosher animal. Since milk of a non-kosher animal cannot create basar b’cholov, it is permitted to cook even kosher meat with such milk and to derive benefit from the mixture (Y.D. 87:3).[7] Accordingly, one may cook kosher meat with non-kosher milk (or vice-versa, non-kosher meat with kosher milk) on behalf of a non-Jew or to feed a pet, provided one addresses issues of maris ayin.

► Kosher Chayos – Meat of a kosher chayah (e.g., a deer) does not become basar b’cholov (mi’d’Oraysa) when cooked with beheimah milk (e.g., venison cooked in cow’s milk).[8] So too, chayah milk does not confer a basar b’cholov prohibition when cooked with beheimah meat (e.g., deer milk cooked with flanken).[9] Rabbinically, however, the mixture is designated basar b’cholov.[10] But that is only with respect to achilah; bishul and hana’ah are permitted when done in a manner that avoids maris ayin (Shach 87:6).

Another qualification for milk to be considered milchig arises from the word eim (mother) itself. Liquid milk remaining in the udder of an animal after it is no longer alive – whether because it underwent a kosher shechita or otherwise died and became a neveilah – is not milchig mi’d’Oraysa, since its source is an animal no longer capable of being an eim (Y.D. 87:6, 90:1).[11]  Mi’derabanan, this milk may not be cooked with meat and, if it was, the mixture may not be eaten. Deriving hana’ah, however, from this mixture is allowed by many poskim.[12]

Milk of a Bas Pekuah

This last exclusion of milk taken from a shechted animal has ramifications for the milk of a bas pekuah. A ben or bas pekuah is a calf born after its mother underwent a kosher shechitah. Halachically, the mother’s shechitah is effective for its yet unborn calf and, mi’d’Oraysa, the calf may be eaten without any additional shechitah, even after it has lived for many years. (As a matter of procedure, on account of maris ayin, halachah requires shechita for a ben pekuah once it walks on the ground, Y.D. 13:2.)  The question is: if a female bas pekuah calf grows into a lactating cow, what is the status of its milk?

Shaar HaMelech (Izmir, 18^th century) and Maharit Algazi (Izmir-Yerushalayim) proposed that mi’d’Oraysa the milk of a bas pekuah is pareve since, after all, it comes from an animal that is halachically classified as a shechutah.[13] On the other hand, the Noda BiYehudah rejected this suggestion, arguing there is no categorical exclusion of milk from a shechutah.[14] Rather, once a cow is shechted, any remaining milk is pareve because the criterion of eemo (coming from a potential mother) is no longer applicable. But a bas pekuah is fully capable of being a mother, and thus its milk is unquestionably milchig.

Milk of Metaphysical Matter

Following the position of Shaar HaMelech that bas pekuah milk is pareve, Mitzpeh Ayson (commentary to Bechoros 6b) finds a creative solution to the question of how Avraham Avinu served his guests butter and milk together with meat (Parshas Vayeira 18:8). The Midrash (cited in Daas Zekeinim) indicates they were served a mixture that, mi’d’Oraysa, constituted basar b’cholov. How could Avraham, who observed all precepts of the Torah before they were formally given (Yoma 28b), benefit from basar b’cholov by serving it to his guests?[15]

Furthermore, the Talmud (Bava Metzia 87a) explains that Avraham removed bread from the menu upon learning it became tamei. If he scrupulously abstained from a merely laudatory practice (not serving tamei food at a non-consecrated meal to assumed heathens), surely, he would have avoided serving milk and meat together – an outright prohibition? These difficulties are resolved by asserting that Avraham’s milk source was a bas pekuah and was actually pareve and not subject to basar b’cholov.[16] This answer, however, is unsatisfactory according to the Noda BiYehudah, who holds that bas pekuah milk is in fact milchig.

An alternate approach is advanced by Malbim (Parshas Vayeira ad loc.). He cites a tradition that Avraham served his guests the meat of a calf he fashioned using the secrets of Sefer Yetzirah.[17] Its meat is pareve because it does not have a mother as a biological precursor. The 19^th century dayan, Rav Shlomo HaKohen of Vilna, in his glosses to Shulchan Aruch (Cheshek Shlomo, Y.D. 98, Shach 6), applies this ruling also to milk taken from such an animal, and to milk formed directly through Sefer Yetzirah. Although identical to cow’s milk, it’s not milchig.

Milk: Deconstructed and Reconstructed

No master of Sefer Yetzirah would dare exploit its supernal wisdom to fashion “dairy‑esque” foods for commercial use. But food manufacturers are actively manipulating microscopic elements in the physical world to produce substances that are nearly chemically identical to dairy derivates. It follows that if artificial milk made through Sefer Yetzirah – which fundamentally shares elemental properties with mammalian milk on the metaphysical plane – is pareve, then certainly, artificial milk made through a physical process with relatively superficial resemblance, should be pareve, too.[18]

Established companies and startups alike are investing heavily in disrupting the dairy industry by putting the cows out to pasture – quite literally. Since the mid-twentieth century, the composition of cow’s milk, one of the most scientifically studied food items, has been identified as comprising approximately 87% water, 4.9% carbohydrates (primarily lactose), 3.4% fat (depending on the breed and diet), 3.3% proteins, and minerals and vitamins. The protein fraction is about 80% casein (digested slowly) and 20% whey (digested rapidly). Various enzymes are a small but important part of the proteins, as well.

It should theoretically be feasible to synthesize this profile in a lab. Water is water. The minerals and vitamins can be gleaned from other natural sources. Plant sugars are not exactly the same as lactose but are a good enough substitute (and superior for those suffering from lactose intolerance[19]). That leaves less than 7% of the entire formulation – the fats and proteins – as uniquely “milk.”

Reproducing the full taste, mouthfeel, and nutritional profile of milk is not yet achievable. Milkfat is incredibly difficult to replicate since it is composed of more than 400 different fatty acids, making it the most complex of all natural fats. Consequently, for now, other sources of fat must suffice. Companies are attempting to synthesize milk proteins (absent their indigenous enzymes) which are ostensibly the components most responsible for providing the primary characteristics of dairy products such as ice cream, yogurt and cheese.

Precision Fermentation: Synthesizing Dairy Proteins

The main method for commercial production of lab-grown casein and whey is through precision fermentation. To understand this process, let’s first review examples of what occurs in regular, natural fermentation:

► Yeast fermentation in winemaking – grape juice is exposed to yeast (a type of fungus, occurring naturally on grape skins or added by the winemaker) which ingests the grape juice sugars and converts them into ethyl alcohol (ethanol) and carbon dioxide (usually released but retained in fizzy varieties), resulting in wine.

► Yeast fermentation in breadmaking – water added to flour activates enzymes (amylase) that break down grain starch into sugars. Yeast transforms the sugars into CO₂  and ethanol (which mostly evaporates during baking). When the gas bubbles are trapped by the grain’s gluten network, the dough rises.

► Bacterial fermentation – bacteria transform carbohydrates into lactic acid to make foods like cheese, yogurt and sauerkraut.[20]

The novelty of precision fermentation is that instead of letting nature decide the outcome of the fungal or bacterial conversion, scientists bioengineer fungi to yield a specific target protein of their choosing.

A foundational step in synthesizing milk proteins took place in the 1990s and 2000s when researchers mapped the bovine genome. Once the DNA sequence to produce milk protein genes was identified, the segment could be amplified using technologies like PCR (polymerase chain reaction). Scientists detach snippets of the cloned gene (via enzymes acting as molecular scissors) and introduce them into fungal DNA. This newly encoded recombinant fungus is placed in a bioreactor – a controlled-environment vessel that facilitates biological processes – where it acts as a fermentation catalyst to convert sugary, nutrient-rich broth into a resultant mixture containing the target protein.

When fermentation is complete, the target protein is harvested and isolated from the mixture using the same filtering and refining technique already ubiquitous in the dairy industry to isolate whey protein from cow’s milk. The synthesized protein is now ready to contribute dairy-like properties to foods. (How cows automatically generate these complex proteins in their rumens – all from plain grass – is truly one of the wonders of Creation!)  

While the application of precision fermentation to synthesize dairy proteins is fairly recent, this technology has been widely used on a commercial scale since the early 1980s to manufacture synthetic insulin, replacing the older, resource-intensive process developed in the 1920s for extracting insulin from cow and pig pancreases.

Precision fermentation’s profound impact on the dairy industry actually goes back to 1990, when the FDA approved a bioengineered food ingredient for the first time, allowing chymosin (also known as rennin) – the enzyme which coagulates milk into curds when making cheese – to be produced synthetically through fermentation. From the dawn of cheesemaking, chymosin was sourced from rennet extracted from a nursing calf’s abomasum (fourth stomach compartment).[21] That classical method has since been relegated to a small niche market. Within a decade, fermentation-produced chymosin (FPC) became the predominant source of cheese coagulant.[22]

Kashrus Considerations

Synthesized dairy proteins are pareve provided all the materials used to synthesize them derived from kosher pareve sources. This is unlike current attempts to produce lab-grown meat, which starts with stem cells obtained from animals. According to the psak of Rav Moshe Heinemann shlit”a, the kosher status of such lab-grown meat products follows its starter material and is subsequently either fleishig or a neveilah.[23]

Fungi, the living organisms responsible for fermentation, are inherently kosher.[24] But as for all fermented foods items, kashrus oversight is needed for the growth media upon which recombinant fungi are propagated and the nutrients they are fed. Moreover, to maintain the very low temperature necessary to keep them alive, the fungal strain is dissolved in glycerin, a kosher-sensitive ingredient, and packed in cryovials. Glycerin is added to prevent the formation of damaging ice crystals, which can rupture cell walls during shipping to production facilities.

At the facility where the fungus-to-protein conversion takes place, the kosher status of bioreactors must be determined in case they were previously used for batches containing non-kosher or dairy components. Finally, the missing fats and enzymes present in natural mammalian milk must be compensated for in final products by adding other kosher-sensitive oils and ingredients.

Some confusion has arisen among consumers about the labeling of foods, like ice cream, where synthetic whey replaces cow-based dairy. Even though the products have no actual dairy content, FDA regulations still require labels to display a dairy allergen warning statement, because the chemical structure of the synthetic version is similar enough to the real thing to potentially trigger an adverse allergic reaction.[25]  Confusion aside, this concern has no bearing on the pareve (or “dairy equipment”) designation of the product.

Final Ruminations

Looking forward, food producers are banking on expanding the range of products made with precision fermentation. They anticipate that other synthetic proteins, mimicking egg whites, seafood, collagen, gelatin, and even meat, will soon join dairy proteins among consumer offerings – all potentially certifiable as kosher-pareve. Nonetheless, even if synthesized proteins replace natural sources, their kosher certification must remain genuine.

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[1] Mishpatim 23:19, Ki Sisa 34:26, Re’ei 14:21. 

[2]Poskim (Y.D. 87:1) dispute whether the Torah’s prohibition of bishul basar b’cholov is limited to cooking in a liquid medium or if it includes other processes involving a fire-based heat source – i.e., roasting and frying. If those are just a Rabbinic prohibition, then only bishul and achilah are prohibited but hana’ah is permitted.

[3] The word pareve belongs to a small set of Yiddish words of Slavic origin. Related to the Polish word para, meaning “pair,” pareve signifies a food that is halachically pairable with either milk or meat.

[4] Cholov sh’keidim, almond milk, mentioned by Rama (Y.D. 87:3), was a widespread beverage and food ingredient in Europe already in the late Middle Ages.

[5] Rama 87:3. See “Optical Allusions: Avoiding Maris Ayin,” by Rabbi Chananya Jacobson, Kashrus Kurrents, Fall 5782/2021.

[6] Shulchan Aruch Y.D. 87:2 and Pri Chadash.

[7] Since cooking kosher meat with non-kosher milk (or kosher milk with non-kosher meat) does not designate the mixture as basar b’cholov, certain leniencies with respect to bitul, nullification, will apply: (1) The Mechaber (Y.D. 92:4) holds – unlike Rama – that chatichah na’aseh neveilah (chana”n) is only for items prohibited due to basar b’cholov and not for other prohibited mixtures or absorptions. Therefore, according to Mechaber, bitul would be achieved with just 60x the absorbed milk and not 60x the entire piece. (2) The stringency of chatichah ha’re’uyah le’hiskabeid, preventing bitul of respectable cuts of meat, is only for pieces classified as intrinsically prohibited (e.g., neveilah or basar b’cholov) but not for pieces that are prohibited due to absorption.

[8] Ten types of kosher animals are listed in the Torah: three are beheimos and seven are chayos. Netziv (Ha’emek Davar, Bereishis 1:24) asserts the distinction between chayos and beheimos is that beheimos have a predisposition to being domesticated while chayos are naturally wild. He challenges the Ramban’s position that their classification is determined by diet.

[9] Following Y.D. 87:3, Shach (4) and Pischei Teshuvah (4).

[10] We explained above that a cooked mixture of meat and milk, in which one component comes from a non-kosher animal, does not create basar b’cholov on any level. In contrast, when one of the components comes from a kosher chayah (or fowl) then, although this mixture is not basar b’cholov mi’d’oraysa, it is basar b’cholov mi’drabbonon.  Therefore, with respect to bitul, the stringencies of chana”n (even according to the Mechaber) and chatichah ha’re’uyah le’hiskabeid apply.

[11] In the event an animal dies without shechitah, whether the milk remaining in its udder is neveilah d’Oraysa or just derabanan is a matter of dispute. See Pri Megadim, S.D. 87:13, and beginning of siman 81. Rav Akiva Eiger (Y.D. 87:6) discusses the milchig status of milk taken from a treifah, according to the view that a treifah is unable to produce offspring and is thus incapable of being an eim. Seemingly, the same discussion would apply to milk from a zekeinah beyond her childbearing years.

[12] Badei HaShulchan 87:77.

[13] Shaar HaMelech, Issurei Mizbei’ach 3:11; Maharit Algazi, Bechoros I:2:6; R. Akiva Eiger, Y.D. 87:6, considers the issue.

[14] Tinyana, Y.D. 36; Yad Yehudah (87:12) also paskens that milk of a bas pekuah is milchig. R. Yosef Engel, Asvan d’Oraysa 14, maintains these conclusions depend on how one understands the halachic mechanics of ben pekuah.

[15] Rav Moshe Heinemann shlit”a (Kuntres Derech Kochav, p. 7, BMG, Lakewood 5775) adduces that serving guests is a forbidden form of hana’ah from the halachah (S.A. Orach Chaim 448:6, M.B. 28)that one may not feed chometzon Pesach even to ownerlessanimals because of the satisfaction one derives from doing so.

[16] Meshech Chochmah accepts this resolution, too. There are various possibilities for why Avraham was not concerned about maris ayin when serving his guests in a way that gave the appearance of benefiting from basar b’cholov. One, is that although maris ayin applies even b’chadrei chadorim – done out of the sight of others – in Avraham’s situation, nobody would perceive a wrongdoing because he was the sole adherent of Torah commandments in the entire world  (Rav Heinemann). Alternatively, Avraham’s observance of Rabbinic injunctions perhaps extended only to those enacted later for specific scenarios, such as eruv tavshilin, but not to prohibitions with broad applications, such as maris ayin.

(See also Lev Aryeh, Chullin 104b, who suggests, in one approach, that the Avos did not adhere to the category of gezeiros that were legislated Rabbinically, as a measure to distance one from the likelihood of transgressing a Torah-level prohibition.

Thus, he did not observe the issur d’rabanan that prohibits the placement of meat and milk on the same table lest one come to eat them together. But whether maris ayin belongs to this class is debatable.)

[17] Chesed l’Avraham (Ein Mishpat, Nahar 51) by Rav Avraham Azulai, great-grandfather of Chida, describes the circumstances which compelled Avraham to form a calf through Sefer Yetzirah to feed his guests. This yields a literal reading of the posuk (18:8), “u’ven habakar asher asah – and the calf that he fashioned” (as opposed to Rashi’s interpretation, “that he prepared”). Incidentally, three generations later, we find Yaakov’s sons fashioning an animal with Sefer Yetzirah whose consumption provoked strife with their brother, Yosef (see Shelah, Parshas VaYeishev).

[18] Rashi (Brachos 55a) explains that the entire Creation, both the spiritual (Shamayim) and physical (Eretz) realms, came into being through permutations of Alef-Beis letters as taught in Sefer Yetzirah. Our observable universe is a physical manifestation of the spiritual worlds formed by tziruf osios. See Rav Moshe Meiselman, Torah, Chazal, & Science, p.57.

[19] Genetically, most Jewish populations are Lactase Non-Persistent (LNP), meaning the small intestine does not produce enough lactase enzyme for digesting lactose past childhood. (Unlike populations of North European extraction, which are predominantly Lactase Persistent.) This condition does not always result in adverse digestive symptoms, such as when dairy is consumed in small amounts. See Genetics of Lactose Intolerance by Anguita-Ruiz, Aguilera, and Gil, https://pmc.ncbi.nlm.nih.gov/articles/PMC7551416/.

[20] Some cheeses also involve a fungal-mold fermentation stage at the end, during ripening. Enzymes, too, play a vital role in all types of fermentation, enriching texture, taste and appearance.

[21] Vegetable rennin sources, such as fig tree sap (mentioned in Rambam, Ma’achalos Asuros 3:14), which produce a more bitter flavored cheese, have also been used in Mediterranean regions since ancient times.

[22] This advent significantly changed the kosher cheese industry, lowering production costs and opening it up to more varieties. Before GMO chymosin, obtaining kosher rennin was a challenge. The main sourcing options were either partially digested milk found in a calf’s stomach, or the actual stomach lining of a properly shechted calf which had to be completely dried to remove its fleishig status. Hence, one of the reasons given for the prohibition of gevinas akum is lest the coagulant was taken from a neveilah (Avodah Zarah 35). In later years, rennin enzyme extracted from the stomach lining in liquid form became common. See Chasam Sofer quoted in Pischei Teshuvah Y.D. 87:19. In the 20^th century, Frankenthal in Bnei Brak had a worldwide monopoly supplying kosher cheese producers with this commodity, which became irrelevant after 1990.

[23] See “It Depends Where They Stem From” by Rabbi Tzvi Rosen, Kashrus Kurrents, Spring 5782/2022.

[24] In 1969, the millions of known fungus species were classified as belonging to their own taxonomic kingdom, alongside plants and animals.

Prior to the invention of the microscope in 1590, identifying fungi as microscopic organisms was not possible. Since then, even if one would deem them a type of miniscule bug, they would be halachically inconsequential. Halachah deals exclusively with the world as observed by the unaided eye of someone with average eyesight and never addresses microscopic materials. See Chochmas Adam – Binas Adam, Hilchos Tolayim 38:49; Aruch HaShulchan 84:36; Iggros Moshe, Yoreh Deah II:146; Halichos Shlomo – Moadim, Pesach p. 176. See also Rav Moshe Meiselman, Torah, Chazal & Science, p. 307.

Accordingly, Rav Heinemann relates in the name of Rav Moshe Feinstein zt”l that food with visible specks is halachically permitted for consumption if one with average eyesight and a basic familiarity of insect structures can identify them as bugs only with the assistance of a magnification aid. Still, mashgichim – who are trained to recognize bug features – routinely use loupes and other magnifiers in their meticulous work of checking vegetables for tolayim. These tools are primarily aids to enhance workflow efficiency, but they also serve to conform with agency policies which tolerate a lower level of infestation prevalence than what basic halacha requires.    

[25] Dairy allergy is unrelated to lactose intolerance.