Mike Tunick puts a yellowish chunk into the metal jaws of a device known as a rheometer.
Slowly, the machine applies pressure to the chunk. The viselike machine squooshes it, causing it to wiggle. Dials on the instrument flutter; a nearby computer printer spits out the results. Mr. Tunick examines the wavy lines on the printout and within seconds has proven what others could only suspect:
The sample is mozzarella cheese.
Mr. Tunick, a chemist at the U.S. Department of Agriculture's Eastern Regional Research Center in Wyndmoor, Pa., has earned a modicum of fame in recent years as one of the nation's foremost food detectives.
Working with sophisticated instruments such as differential scanning calorimeters and rheometers, he has developed telltale scientific fingerprints of common cheeses. By comparing suspect cheeses with these fingerprints he has provided evidence that has been used to convict corporations of adulterating food.
On the basis of evidence he analyzed, Dakota Cheese Inc., a South Dakota company, and its president, James Dee, were fined $515,000 in 1989 for illegally doctoring 2 million pounds of mozzarella cheese sold to the United States government.
More recently, he demonstrated that Cheddar cheese, disguised Cheshire cheese, was being illegally imported into the United States through Philadelphia.
Mr. Tunick is one of more than 200 agricultural scientists who work at the 27-acre center, which recently celebrated its 50th anniversary.
While food sleuthing is one of the most dramatic tasks that the center's scientists undertake, it is not the facility's primary mission. The center, one of four regional research centers set up by an act of Congress in 1938, was established to conduct basic and applied research on milk, meat, fruits, vegetables, animal hides and other products.
Scientists at the Wyndmoor lab, which is housed in a U-shaped building that resembles an aging red brick high school, have helped develop instant mashed potatoes, lactose-reduced milk products, longer-lasting apple cider, better-tasting maple syrup and many other improved food products.
While much of the research has benefited people, not all of the products developed there have been commercial successes.
During World War II, scientists at the center developed ways to produce rubber tires from Russian dandelions. "It never took off," said John P. Cherry, the laboratory's director since 1984. "But the technology was developed and could still be used if there ever was a need for it."
During his career as a food scientist, Mr. Cherry helped develop ways to make cookies from chicken feathers and hamburgers from cotton seed. Neither was a commercial hit, but Mr. Cherry noted that about 3 percent of the food given to chickens today is made from recycled chicken feathers.
A major focus of the center continues to be on developing ways to improve the safety of food. The center's scientists developed ways to reduce the levels of nitrosamines, a suspected cancer-causing agent, in bacon and ham. They developed guidelines to improve the safety of home canning, ways to reduce the residues of toxic chemicals in meats and methods to reduce the incidence of botulism in children.
Today, one of the center's major food-safety focuses is on developing ways to reduce the growth of salmonella, listeria, shigella and other harmful microorganisms during food processing.
Bob Buchanan, a microbiologist, said that microorganisms account for between 2 million and 50 million cases of food poisoning in the United States each year. He is developing computer models that will enable processors to predict when microorganisms will grow to unsafe levels and thereby help them to design safer systems.
Another thrust of the agricultural center is to develop new food products. Walter Fiddler, a food scientist, said the center is currently testing the flavor and safety of hot dogs that are made partly from Alaskan pollock.
"So far, it looks feasible," he said. "Hot dogs made with fish proteins appear to be less expensive and more healthful than those made with traditional ingredients."
One of the center's major accomplishments has been the development of milk and cheese products that contain low levels of lactose, a milk sugar that tens of millions of Americans cannot digest. Scientists say that more than one-third of the United States' population suffers from some degree of lactose intolerance resulting in gas, bloating, diarrhea, nausea and other health problems.
Studies show that 50 to 75 percent of American minorities suffer from lactose intolerance. Asians, blacks, American Indians and Latinos are particularly susceptible to the ailment, which is believed to be genetically linked.
As the result of research conducted by Virginia Holsinger, George Somkuti and other scientists at the center, milk, cheese, yogurt and other dairy products have been developed that contain low levels of lactose.