Mary Engle Pennington

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Mary Engle Pennington

Mary Engle Pennington (1872-1952), a chemist and bacteriologist, was a pioneer in the advancement of the preservation of perishable foods during the first half of the 20th century.

Mary Engle Pennington was born on October 8, 1872, in Nashville, Tennessee, the elder of two daughters born to Henry and Sarah B. (Molony) Pennington. A few years after her birth, Pennington's family moved to Philadelphia, Pennsylvania, to be closer to her mother's relatives, a well-to-do Quaker family. Her father established a successful business in label manufacturing, and the family lived in a three-story red brick house near the University of Pennsylvania. Her parents were very supportive of their daughters and encouraged them to pursue their interests. As a youngster, Pennington learned to garden, a hobby she shared with her father and maintained throughout her life.

Pennington also enjoyed reading and spent considerable time at the public library. When she was 12 years old, she came across a book on medical chemistry that sparked her interest, and she spent the summer studying the chapter on nitrogen and oxygen. "Suddenly, one day," Pennington told the New Yorker in 1941, "I realized, lickity hoop, that although I couldn't touch, taste, or smell them they really existed. It was a milestone." Unfortunately, in the late 19th century, girls were discouraged from studying science. When she approached the headmistress at the all-girl boarding school she attended and demanded that she receive instruction in chemistry, Pennington was flatly denied— such pursuits by women were considered wholly inappropriate and decidedly unladylike.

Studied Chemistry and Biology

When Pennington returned from school in 1890, her desire to study chemistry was unabated. Refusing to concede to the social standards of the time, the 18-year-old woman went to the dean of the University of Pennsylvania and asked that she be admitted to the school of science. The dean was impressed and agreed, and Pennington became a student of the university's Towne Scientific School, where she studied chemistry, biology, and hygiene. Two years later she completed the requirements necessary for a bachelor's degree; however, the board of trustees, who disapproved of a woman's presence at the university, refused to grant her a diploma. Instead, she was given a certificate of proficiency in biology.

Because she did not hold a bachelor's degree, Pennington was ineligible for graduate studies. This technicality was circumvented with the support of the faculty who invoked a seldom-used university statute that allowed special students to be enrolled in graduate studies in extraordinary cases. Thus, Pennington became a doctoral student in the university's electrochemical school and studied under Edgar Fahs Smith. She was awarded a Ph.D. in 1895; her dissertation was a study of the derivatives of the elements columbium and tantalum. After spending an additional two years at the University of Pennsylvania studying chemical botany, Pennington accepted a one-year fellowship at Yale University, where she studied physiological chemistry, teaming with Russell Chittenden to examine the effect colored light had on plant growth.

A Bacteriological Chemist

In 1898 Pennington returned to Philadelphia and accepted a position as an instructor in physiological chemistry at Women's Medical College, a position she retained until 1906. At the same time she began making plans to open her own business. Securing commitments from some 400 local doctors, each of whom agreed to give her at least $50 in business annually, Pennington partnered with university colleague Elizabeth Atkinson and opened the doors to the Philadelphia Clinical Laboratory in 1901. The laboratory, which conducted bacteriological and chemical analyses, was quite successful, and Pennington began to develop a reputation for her work.

In 1904 she was asked to head the bacteriological laboratory for the Philadelphia Department of Health and Charities. There Pennington focused the energies of her small staff on the problem of unsafe milk. Carefully examining all phases of milk production, she established basic standards for the industry that were adopted first statewide and eventually throughout the country. She also studied the preservation of milk at low temperatures. During this time, Pennington's persuasive abilities came to light. With no laws to enforce safe handling or storage, she nonetheless convinced local ice cream vendors who sold their good from carts mainly to children to adopt more sanitary measures by showing the vendors microscopic slides of the bacteria growth on their equipment. Convinced, vendors agreed to disinfect their pots and utensils by boiling them.

Created Standards in Food Safety and Handling

At the turn of the 20th century, refrigerated foods were highly suspect among the public. As cities grew, the demand for foods transported over longer distances and stored for longer periods of time also increased. However, there existed no standards for safe food handling or storage. As a result, many refrigerated or frozen products that entered the market were not safe. Hundreds died and thousands more became ill every year after consuming spoiled foods. Of special concern were eggs, milk, poultry, and fish. Along with the safety issues, the public complained that preserved perishables were poor in quality and taste, arriving either dried out or moldy. Pennington entered the field of refrigeration in 1905 when Dr. Harvey W. Wiley, a family friend and chief of the U.S. Department of Agriculture's Bureau of Chemistry, asked her to join his staff and study the effects of refrigeration on behavior of perishable foods.

The passage of the landmark Pure Food and Drug Act in 1906 was the beginning of government regulation of food safety. However, no standards existed and the terms "safe" and "unsafe" lacked scientific definition, thereby rendering the new law unenforceable. As a result the Bureau of Chemistry decided to establish the Food Research Laboratory, which would conduct research that would provide scientific standards for food safety, particularly for milk, poultry, eggs, and fish. The data collected would be used both as evidence in the prosecution of food dealers who failed to comply with the act and as a resource for those in the industry who desired to implement reforms to avoid coming under the scrutiny of the government.

Chief of the Food Research Laboratory

Wiley believed Pennington was the perfect person to head up the new laboratory. However, she remained skeptical that the government would award the position of chief of the Food Research Laboratory to a woman. Wiley nonetheless convinced her at least to take the Civil Service examination required for the position. Unbeknownst to Pennington, Wiley submitted her exam under the name M. E. Pennington, a fact that later infuriated Pennington when she found out. She scored highest on the exam and was offered the job. Upon her acceptance, the Civil Service discovered that M. E. Pennington was in fact Ms. Pennington and the offer was revoked. However, Wiley stepped in on her behalf and convinced the Civil Service to hire Pennington despite her gender.

Wishing to remain outside the fray of Washington politics, Pennington set up her office in the same building that housed the Philadelphia Clinical Laboratory and then got busy with her assignment. She studied every stage through which chicken passes on the way to the consumer, including the slaughterhouse and packinghouse, during transport from the wholesaler to the retailer, and the storage conditions provided by the retailer. Pennington believed that in order for cold-stored poultry to arrive safely on the consumer's supper table, each step of the process must provide a properly refrigerated and hygienic environment. She also examined the poultry carefully to discover the signs of deterioration. She took note of visual changes in color and texture and performed chemical and microscopic examinations to detect other changes, such as fat acidity. Her research led her to establish that poultry could be safely stored and retain a high quality of flavor for up to one year at a temperature of zero degrees Fahrenheit.

Through her hands-on research in slaughtering chickens, Pennington established that piercing the chicken's brain with a small knife and cutting the jugular veins from the inside was more effective than the traditional block-andaxe method because, for reasons unknown, piercing the chickens made them easier to pluck, thus causing less damage to the chickens before transporting them. The process also left the chickens intact, which lessened the chance of bacterial growth. Along with changing the basic strategy for slaughtering poultry, she also transformed the transportation system. Chickens were normally packed in barrels of chipped ice to be shipped. However, by the time they arrived, the chickens were often waterlogged, floating in tepid water. Pennington devised a way to extract the heat from the slaughtered chickens so that they could then be dry-packed in boxes and transported in refrigerated train cars.

During her tenure with the Food Research Laboratory, Pennington instituted basic standards for the sanitary handling of eggs. She encouraged farmers to collect eggs, which are highly perishable, more frequently in warm weather and is credited with the invention of the modern egg crate, which she designed to protect the eggs in transport. In 1911 the H. J. Keith Egg Company sued the U.S. Department of Agriculture (USDA) for libel after the USDA seized over 400 cans of liquid eggs declared to be dangerously decomposed. Cracked, oversized, or otherwise scarred eggs were commonly shipped to egg-breaking plants where they were frozen, canned, or dried and then sold to bakers and confectioners. The unsanitary practices of the egg-breakers led to high levels of bacteria in the product. Because no legal or scientific standards existed to back the government's claims, the USDA called upon Pennington to investigate. Once again, she started from the very beginning, at the farms that produced the eggs, and followed the eggs into the egg-breaking plants and through the transportation system.

Due to flaws in the legal wording of the Pure Food Act, the USDA lost its court battle against H. J. Keith. However, Pennington won over the egg-breaking industry using her natural gift of persuasion and scientific logic. She convinced three plants to adopt her methods of sanitization and refrigeration, arguing that such ventures would earn the public's trust. When those plants were overwhelmed with orders, other egg-breakers followed suit. According to Lisa Mae Robinson in Agricultural History, Pennington relied on "personal persuasion of individual plant owners and warehousemen to improve conditions and encourage stricter standards. She encouraged these people to see that their livelihood depended on consumer confidence in their products and that such confidence could only be won by turning out a superior product."

Along with substantially affecting the poultry and egg industries, Pennington also reformed the methods of processing fresh fish. She created a standardized system for scaling, skinning, quick-freezing, and dry-packing the fish immediately after they were caught.

Advancements in Refrigeration

During World War I Pennington served as a consultant for the Perishable Products Division of the U.S. Food Administration. The government had 40,000 refrigerated train cars available for transporting perishables. Research conducted by Pennington revealed that only 3,000 of those cars had proper air circulation and refrigeration. After taking some 500 train trips, during which Pennington studied the effects of extreme heat and cold on a variety of perishables, she established the important link between humidity and food preservation. According to Ethlie Ann Vare and Greg Ptacek in Mothers of Invention, "Pennington didn't actually invent refrigeration, but she made it workable. Like the atmosphere outside, air within a refrigerated locker would lose its ability to hold moisture as it approached freezing temperature. The result was dried-out food; yet, when humidity was increased, the food became moldy." By monitoring humidity levels, along with attending to proper insulation and air circulation, the quality of refrigerated foods could be greatly enhanced. Pennington was awarded a Notable Service Medal in 1919 for her contribution to the war effort.

Became Independent Consultant

In 1919 Pennington left the Food Research Laboratory and moved to New York to run the research department of the American Balsa Company, a manufacturer of insulation. Three years later she opened a business as a consultant to food storage and shipping companies. Highly successful, by 1936 she had moved her office to the prestigious Woolworth Building. She studied frozen foods and developed improvements for commercial and home refrigeration systems. She even managed to convince several major universities to incorporate courses on household refrigeration. With no textbooks to be had, Pennington then created 13 pamphlets, with such catchy titles as "Journeys with Refrigerated Foods" and "The Romance of Ice," to be used in the classroom.

Pennington never married and was a lifelong active member of the Society of Friends. She wrote numerous articles and technical papers during her career and co-authored Eggs (1933). She also held two patents with A. B. Davis for insulating material. During the final years of her life, she enjoyed knitting, sewing, and gardening on the terrace of her Riverside Drive penthouse, which she shared with a Persian cat named Bonny. Her kitchen was completely electric, uncommon at the time, and she proudly ate frozen, refrigerated, and canned products as part of her everyday diet. Pennington, who never retired from her consulting business, died of a heart attack on December 27, 1952. She was buried in Philadelphia.


Garraty, John A., and Mark C. Carnes, editors, American National Biography, Oxford University Press, 1999.

McGrath, Kimberly A., editor, World of Invention, 2nd edition, Gale, 1999.

McMurray, Emily, J., editor, Notable 20th-Century Scientists, Gale, 1995.

Shearer, Benjamin F., and Barbara S. Shearer, editors, Notable Women in the Physical Sciences: A Biographical Dictionary, Greenwood Press, 1997.

Vare, Ethlie Ann, and Greg Ptacek, Mothers of Invention. From the Bra to the Bomb: Forgotten Women and Their Unforgettable Ideas, Morrow, 1987.

Zierdt-Warshaw, Linda, Alan Winkler, and Leonard Bernstein. American Women in Technology: An Encyclopedia, ABC-CLIO, 2000.


Agricultural History, Spring 1990.

New Yorker, September 6, 1941. □

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Mary Engle Pennington

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