When Science Meets Kashrut: How one woman blazed a trail in OU Kosher

At a bar mitzvah in Englewood, New Jersey, in the mid-1980s, Rabbi Menachem Genack, early in his career as rabbinic administrator of OU Kosher, was introduced to Dr. Judith Leff, a biochemist who was then working as a researcher in molecular biology at the Albert Einstein Medical College of Medicine in the Bronx.

The rabbi did not know Dr. Leff, but he knew of her. About two decades earlier he had been among a few young men who rented a room in Boston from Zelda Leff, Dr. Leff’s mother-in-law.

The rabbi’s conversation with Dr. Leff eventually turned to her scientific specialty—which included the technology of food ingredients—and Rabbi Genack thought that her knowledge could be useful to the OU’s increasingly high-tech kashrut work. He invited her to work for the OU as a food chemistry consultant. She accepted the offer.

For the next few decades Dr. Leff, an ingredient technology specialist, served as a go-to expert in the kosher production and supervising industry for people with questions about what went into—or was proposed to go into—products made under kosher supervision, particularly by the OU.

Dr. Leff, a native of Vienna, who has lived in France, Israel and Passaic, New Jersey—and back in Jerusalem since the death of her husband, Dr. Nosson Chaim Leff, a professor of economics at Columbia University—was, for most of her career, a rare female presence in the kashrut business that tends to be dominated by male rabbis and mashgichim.

Dr. Leff, who became interested in science as a child, received her PhD in plant physiology from the Hebrew University of Jerusalem. During her career she did microbial chemistry research at Hadassah Hospital in Jerusalem, as well as at several universities in the United States, including Harvard, Tufts and Brandeis.

Dr. Leff brought both a female touch and a scientific emphasis to OU Kosher and its educational activities conducted in the Jewish community, which was started a century ago by the members of the Women’s Branch of the OU to encourage observance of kashrut.

In addition, Dr. Leff says, her obvious technical knowledge was an advantage at production facilities. “When I visited factories,” she says, “the product managers were grateful that we were speaking the same language, and they had more respect for the kashrut organization [that she was representing].”

Dr. Leff, well-known in the world of kashrut experts, was an in-demand speaker at professional kashrut conferences, a respected behind-the-scenes expert on kosher food production and was acknowledged by the rabbis who often sought her opinions.

Dr. Leff’s consultancy was “very important . . . extremely helpful,” says Rabbi Moshe Elefant, COO, OU Kosher. She supplemented the supervision work of rabbis who were not trained in food technology. Before she joined the OU, he says, “we did not have that [degree of] knowledge.”

Dr. Leff brought both a female touch and a scientific emphasis to OU Kosher.

As part of her work at the OU, which largely was before the internet made her understanding of food’s chemical components more readily available, she helped develop and establish the agency’s Ingredient Approval Registry and the Universal Kosher Database, massive collections of certified ingredients and products that serve as invaluable resources for anyone in the kashrut business.

One OU mashgiach called Dr. Leff “just a wonderful human being, an exceedingly professional . . .  educated and knowledgeable person in the area of food manufacturing . . . Rabbis were able to make decisions based on the wellsprings of her knowledge.”

“She made a unique contribution [to kashrut observance],” says Rabbi Avrohom Juravel, rabbinic coordinator for technical services at OU Kosher.

Dr. Leff’s specialty was educating kashrut professionals and the general public to have an understanding of the increasingly complex relationship between kashrut requirements and the challenges presented by emerging high-tech food production techniques.

“We are witnessing today a veritable revolution, both in the scope of food technology and in the source of food ingredients . . . the basic technology used to produce food ingredients has undergone a remarkable transformation,” Dr. Leff wrote in a 1994 Jewish Action essay titled, “The Modern Food Industry and Kashrus: Today’s new foods are high-tech, but are they kosher?”

“Kashrut questions arise at all stages of a biotechnology product,” she continued. “Our posekim face new challenges, and they are devoting increasing attention to resolving these issues.”

She expanded on this theme in a 1996 Jewish Action essay, “Do Natural + Wholesome = Kosher?”: “Natural ingredients carry a hefty financial premium, so there are strong incentives to cheat,” she wrote.  “In this case, however, replacing a ‘natural’ ingredient with one derived from petrochemicals is good for kashrut. . . . Everything I ever learned in my life was used in my work in kashrut,” Dr. Leff says. “I pride myself on having brought the awareness of the kashrut aspects of the many thousands of ingredients used in food manufacturing, including those produced by means of biotechnology.”

“I was there at the right time, in the right place” to advance the role of science in kashrut, she says.

Steve Lipman is a frequent contributor to Jewish Action.