On Yom Tov there is a special mitzvah to rejoice. “You shall rejoice on your festival – you (i.e., the husband and wife), your son, your daughter, your slave, your maidservant, the Levite, the convert, the orphan, and the widow who are in your cities” (Devarim 16:14). For male adults, enjoyment is achieved by eating meat (Rambam, Hilchos Yom Tov 86:18) and drinking wine, for adult females it is achieved by purchasing new garments and jewelry, and for children it is through eating candies and nuts (Pesachim 109a; Orach Chaim 529:2). On Rosh Hashanah, HaShem designates a person’s financial income for the upcoming year. Lest one think that the extra expenditures to enhance enjoyment on Yom Tov will detract from the family savings, we are assured to be financially reimbursed for such Yom Tov expenditures (Beitza 16a). When the Beis HaMikdash stood, the mitzvah of rejoicing on Yom Tov was fulfilled by eating meat of the korban shelamin offering (Chagigah 1:4). Because of the concept that “there is no joy, except with meat and wine” (Pesachim 109a), Yom Tov meals focus on meat. Those who prefer chicken or turkey are entitled to use those foods to fulfill requirement of “enjoyment” (see Rabbi Ari Enkin, 2012). The focus on meat, chicken, or turkey limits the consumption of dairy products on Yom Tov.

The laws of basar b’chalav are derived from the phrase “you shall not cook a kid in its mother’s milk,” repeated three times in the Torah (Shemos 23:19, 34:26; Devarim 14:21). Only meat from a kosher domesticated animal species and milk from a kosher domesticated animal, when cooked together become basar b’chalav. The trice repetitions ignite three distinct prohibitions: a person may not cook basar b’chalav, may not eat basar b’chalav, and may not derive benefit from basar b’chalav. The prohibitions of basar b’chalav are unique, in that each food by itself is permissible, yet it is in the cooked combination that it takes on a new status of being prohibited. Recognizing the uniqueness of this, Chazal termed this a chidush (a novelty) (Chullin 108a). The cooking of meat and dairy together created a new halachic entity, termed basar b’chalav (Forst, 1991).

Two of these prohibitions I unknowingly may have encountered in teaching laboratory sections of Microbiology. A specific exercise was to discern bacteria that secrete proteolytic (protein degrading) enzymes that catalyze the hydrolysis of casein, a milk protein, to amino acids, which are then transported into the bacterial cell. Not all bacteria are capable of the extracellular digestion of casein. The protocol involved adding sterile skim milk to a hot molten agar medium (held at 55°C) in a Petri dish, mixing, letting the medium solidify, and then inoculating various bacteria on the surface of the medium. In one version of this exercise, milk was added to Nutrient Agar, which is a general microbiological growth medium containing a digest of bovine skeletal muscle. An astute student questioned whether this protocol violated the prohibitions of cooking basar b’chalav and of getting benefit from basar b’chalav. Assuming that the undergraduate was correct, the protocol was modified by using Tryptic Soy Agar, a general microbiological growth medium containing digest of soy, instead of meat, proteins.   

Rav Y Nachshoni (1989) noted that although most Biblical commentaries concluded that basar b’chalav is a chok, or, a commandment that is unfathomable by human logic, still logical explanations were sought. This is in accord with Rambam’s recommendation that although a law was designated as a chok, an individual should employ ingenuity to speculate on a potential rationale for the law (Hilchos Temurah 4:13). Rav Nachsoni summarized the speculations put forth by various commentaries.

1. Ramban: the prohibition of basar b’chalav is because we are a holy nation and because it prevents cruelty.


2. Chinuch (mitzvah 92): the combination of meat with milk is physically and spiritually harmful.


3. Rabbenu Bechayei: meat and milk are harmful when consumed together. He connected this prohibition to the prohibition of consuming blood. According to Rabbenu Bechayei, mammalian milk is derived from the animal’s blood and milk resumes its original identity (as blood) when mixed with meat. 


4. (d)   Rav Samson Raphael Hirsch (in Chorev): HaShem created every species “after its own kind” (Bereshis 1:!2) and forbade the mixing of certain species, including interbreeding different species of livestock, shaatnez, interspersing fruit trees and grapevines in one field, allowing a donkey and an ox pull a plow together, and mixing meat with milk.


5. Rav Isaac Breuer (in Nachliel) categorized basar b’chalav as belonging to a “Torah of nature.” Just as mankind must be sanctified through mitzvos, so too, must nature.


6. Rambam (Moreh Nevuchim 3:48): the combination of meat with milk played a role in ancient pagan rites. Although Rambam noted that he was unable to find a source for such a custom among ancient pagans, Rav Menachem Kasher (Torah Sheleimah, vol. 19, appendix 21) noted that Rambam’s theory was verified with the 1928 discovery of the Ras Shamra tablets which described such a ritual (cited in Silberberg, 2012)).


7. Abarbanel: idolatrous shepherds convened twice a year to discuss current issues of shepherding and at these gatherings, meat with milk was consumed together. The prohibition of basar b’chalav was to keep Jews distinct from idolatrous practices.


8. Rav David Tzvi Hoffman: basar b’chalav is identified with the Jewish concept of abstaining from permitted foods, so as to raise one’s spiritual level.

Rav Nachshoni concluded, “There is no absolute logic to the separation of meat and milk. It belongs among those laws that we cannot comprehend with our logic.” Rabbi David Silverberg (2012) reviewed the approach taken by the Ralbag. “When one boils an animal in milk, he uses that which nurtured it and helped it grow to destroy it. And this is precisely the message the Torah seeks to convey through the prohibition - that we must not allow the blessings of the world given to us for our benefit, as a means of our destruction.”

An interesting exchange of letters regarding basar b’chalav appeared in the Journal of the American Medical Association. Dr. M. Chamurich (1961) suggested that the rationale of basar b’chalav was based on avoidance of brucellosis, a zoonosis (an infectious disease transmitted from animals to humans or from humans to animals) caused by Gram negative bacteria of the genus, Brucella. Transmission is via ingestion of infected food, direct contact with an infected animal, inhalation of bacterial-laden aerosols, and consumption of unpasteurized milk products. There are different species of Brucella, each with a slightly different host specificity:  B. melitensis infects goats and sheep, B. abortus infects cattle, and B. ovis infects sheep. In humans, brucellosis is characterized by fever, muscular pain, and sweating (Wikipedia, 2012a). The Chamurich letter triggered a response from Dr. M.M. Stern, which began “I am astonished to read in The Journal, Jan. 14, page 163, Dr. Morris Chamurich’s letter about the biblical reason for forbidding the use of milk and meat.”  The letter continues to explain that the rationale of basar b’chalav is not hygienic in nature, but rather is a prohibition linked to avoidance of rites common in pagan cults (similar. to the explanation of Rambam). 

David Israel Macht (1882-1961), is an interesting personality, who, in the early to mid-twentieth century in the United States, took it upon himself to “defend” Torah. Born in Moscow, he was brought to the United States as a child and apparently developed interests in science and medicine. In 1906 he received an M.D. degree from Johns Hopkins University and pursued postgraduate training at Harvard and thereafter in Berlin, Munich, and Vienna. In 1908 he joined the faculty of Johns Hopkins University, focusing on pharmacology and remained there until 1932. Thereafter, he was a director of pharmaceutical research for a pharmaceutical firm and from 1933 to 1943 was a visiting professor of physiology at Yeshiva College of Yeshiva University. He was a scientist who “strongly believed there was no contradiction between Judaism and science and a number of his publications presented experimental proof in support of this view” (Wilk, 1983).  Macht (1940) tackled the basar b’chalav issue and sought to find subtle adverse health effects from its consumption. He compared the toxicities of meat extracts, dairy extracts, and combinations of meat/dairy extracts and demonstrated that milk and meat mixtures when injected into mice, rats, and other animals exhibited synergistic (i.e., potentiated) toxicities, as compared to milk and meat extracts injected alone. Similar synergistic interactions were noted when combinations of meat juices and milk were administered by stomach tube to rabbits, as compared to similar dosages administered singly.

Other interesting research conducted by Macht included the following, (a) He performed studies  on laboratory animals to show that shechitah was a most merciful method of slaughter than other means of sacrificing an animal. (b) Using a plant-based assay, he showed that kosher food (meat, fish, etc.) was less toxic than non-kosher foods and that blood from an animal slaughtered by shechitah was less toxic than blood obtained from animals sacrificed by other methods. And (c) he removed the spleens of mice and showed that these mice had increased running speed, as compared to control mice. This research confirmed an incident in the story of Adoniya’s attempt to seize the throne from his father, King David. In Adoniya’s coronation ceremony, 50 men ran before his chariot (I Melachim 1:5); to enhance their running speed, Adoniya surgically removed their spleens.  

“Chazal were not satisfied with the prevention of meat and dairy being eaten together. They decreed that dairy may not be eaten even after eating meat unless one waits a specific period of time” (Forst, 1991). The source is Chullin (105a): “Rav Chisda said: If one ate meat, he is forbidden to eat cheese afterwards.” Rashi explained that meat exudes fats, which cling to the oral cavity and are difficult to remove, causing the taste of fat to linger in the mouth. Rambam, on the other hand (Hilchos Maachalos Asuros 9:28), held that the rationale for waiting is to negate the effect of meat lodged between teeth. The Talmud continued, Mar Ukvah said, “I would not eat cheese in the same meal as meat; I would each cheese in the next meal.” The time between meals was estimated at 6 hours, which was adapted by poskim as the rationale for waiting 6 hours between meat and milk. Apparently, it was felt that after the passage of 6 hours, the fatty residue in the palate and throat was dissolved by saliva and meat slivers between teeth were sufficiently decomposed to no longer be considered meat 

Decomposition of fat and meats in the human oral cavity is governed by enzymes in saliva. Primarily composed of water (98%), saliva is produced in and secreted from three pairs of salivary glands - the parotid gland, the sublingual gland, and the submandibular gland. The remaining 2% of saliva consists of electrolytes, mucus, glycoproteins, antibacterial agents (i.e., lysozyme, secretory immunoglobulin A, lactoferrin, peroxidase, and thiocyanate) and enzymes. The main enzyme is salivary amylase, which functions in the decomposition of starch to simple sugars and, thus, is involved neither with the hydrolysis of meat proteins nor of fats. Also produced in the salivary gland is lipase, an enzyme that decomposes fats (Wikipedia, 2012b). The hydrolytic activity of lipase accounts for Rashi’s hypothesis that the time limit between meat and milk is based on the disappearance of fatty residues from the palate and throat. Meat is primarily protein with varying degrees of fat. Salivary proteases, needed for decomposition of meat proteins, are generated from polymorphonuclear leukocytes (i.e., white blood cells) and bacteria in the oral cavity (Ingman et al., 1998). Protease activity would explain Rambam’s view regarding the decay of meat lodged between teeth. Anyone who has had meat lodged between his teeth knows that it does not rapidly decay. Enzymatic activity is related to the surface area of the substrate, with the greater the surface area of a substrate, the more rapid the hydrolytic activity of an enzyme. Proteases, thus, are more efficient in the decomposition of small particles of meat, as compared to a sliver of meat lodged between one’s teeth. Hence, such slivers tend to remain lodged between teeth.

Rabbi Forst (1991) provided a practical difference between the view of Rashi and that of the Rambam. According to Rashi, after waiting 6 hours between meat and milk, if one finds a piece of meat between his teeth, the meat must be removed prior to consuming dairy. As according to Rashi, meat is not expected to decompose in the oral cavity after a 6 hour period.  However, according to Rambam, the intent of waiting 6 hours is to allow the meat to decompose. Thus, meat remaining in the mouth for 6 hours or longer has lost the status of meat and one may consume dairy without removing the meat. As noted by Rabbi Forst, the practical halachah is to follow both the views of Rashi and of Rambam. After waiting the 6 hour period, if one finds meat between his teeth, then, prior to eating dairy, the meat should be removed, the mouth should be cleaned by eating bulky parve food, and the mouth should be rinsed.

References:

Enkin, A., 2012, torahmusings.com/2012/03/simchat-yom-tov/, March 22nd.

Chamurich, M., 1961, Biblical reason for forbidding use of milk and meat, JAMA 175:163.

Forst, B., 1991, The Laws of Kashrus, Mesorah Publ., Ltd, Brooklyn, NY.

Ingman, T. et al., 1993, Salivary collagenase, elastase- and trypsin-like proteases as biochemical marker  of periodontal tissue destruction in adult and localized juvenile periodontitis, Oral Microbiol. Immunol., 8:298-305.

Macht, D.I., 1940, The Bible as a source of subjects for scientific research, Med. Leaves, 3:174-184.

Nachshoni, Y., 1989, Studies in the Weekly Parashah, Sh’mos, Mesorah Publ., Ltd., Brooklyn,  NY.

Silverberg, D. (retrieved 2/20/2012), The Israel Koschitzky Virtual Beit Midrash, Parashat Ki Tisa - Purim, Yeshivat Har Etzion, http://vbm-torah.org/archive/salt-shemot/21-1kitisa.htm

Stern, M.M., 1961, Biblical reason for forbidding use of milk and meat, JAMA 176:467.

Wikipedia (retrieved 4/1/2012), (a) Brucellosis; (b) Saliva.

Wilk, D., 1983, David Israel Macht, Koroth, 8:305-317.