He’s a Sleuth on the Trail of Fraudulent Foods : Labeling: Chemist uses technology to verify and identify cheese ingredients.

Like Sherlock Holmes, Michael Tunick uses reasoning, not intuition, to catch his culprits. Tunick, a chemist here at the U.S. Department of Agriculture’s Eastern Regional Research Center, isn’t sleuthing for stolen gems or murder weapons, however. He’s after suspect cheese.

Take the case of the bogus mozzarella. The tip-off to USDA inspectors was the bags of imported calcium caseinate in the warehouses of a South Dakota cheese firm. The company was supposed to be supplying mozzarella to the school-lunch program.

Calcium caseinate is a powdery white substance refined from milk and used widely as an ingredient in imitation cheese. A few years ago, when the international supply of milk was at a huge surplus, calcium caseinate was dumped on the world market for a fraction of what it cost to make.

With this inexpensive milk derivative, cheese could be made for about a third less than with unrefined milk.

Tunick compared the melting properties of fat in real and imitation mozzarella by using a method called differential scanning calorimetry. In short, the fat in cheese with calcium caseinate does not soften as much.

Another method, which magnifies the fat globules in the cheeses, verified these findings. The fat in imitation cheese accumulates in a jumbled heap, whereas fat in natural cheese disperses more uniformly.

Last year the cheese company and its president were each fined $200,000 in U.S. District Court for defrauding the federal government.

Another case Tunick cracked was that of the imported “Cheshire.” When U.S. Customs officials unloaded a shipment of cheese in Philadelphia, it was an unusual yellow color.

Tunick said he believes Customs was doubly suspicious because the U.S. import quota for Cheddar cheese from the European Common Market had been reached, and it was altogether possible that this was Cheddar masquerading as Cheshire. A chunk of the mysterious cheese was sent to Tunick.

It arrived here at USDA’s labs in a suburb of Philadelphia, one of the agency’s 120 national agricultural research facilities, and home of the invention of the instant potato flake.

A 1940s building resembling an aging red-brick high school, the facility houses dozens of labs crowded with beakers and vials. Tunick’s work area also contains a refrigerator filled with chunks of cheese labeled with government identification numbers.

Using a scientific method called rheology, or the study of the flow of matter, Tunick measured the elasticity and viscosity among samples of cheese he knew were Cheddar and Cheshire.

In simpler terms, the measurements quantify the crumbliness of the cheese when it’s subjected to stress and strain. A quarter-sized disk of cheese is squished in a metal contraption; a computer measures what happens to the cheese when force is applied.

To most people, the gently descending lines on the computer readouts would look like a map of a ski slope for beginners. But to Tunick, the slope--translated into the conclusion that Cheshire crumbles more easily than Cheddar--yields a specific mathematical equation. The sample from Customs matched the slope of the Cheddar.

Tunick relayed his results to Customs, which is still litigating the case. But his evidence provided what the sense of taste can only suspect. After all, Tunick pointed out, a simple taste test of the Cheshire wouldn’t stand up in court.

Imitating a lawyer in a courtroom, Tunick said, “I think it tastes like Cheddar.” The other lawyer answers, “Objection. I think it tastes like Cheshire.”

A similar case came up earlier this year, only this time the cheese, imported from Ireland, was simply labeled “hard cheese.” Customs didn’t know what it was, Tunick said. And neither did Tunick.

“It didn’t meet the standard for anything. It had too much fat to be provolone and too little moisture to be Parmesan or Romano.” Tunick told Customs his verdict, but he’s not sure what the agency is going to do about it.

Periodically, Tunick gets samples from another USDA lab in Chicago to test butter that is suspected of containing margarine. Other scientists at the USDA lab have caught cows’ milk being illegally used in cheese labeled as goats’ cheese, and buttermilk powder containing types of milk powders other than buttermilk.

Being a cheese whiz is not Tunick’s sole job; in fact, nowadays his primary responsibility at the research center is coming up with better-tasting low-fat cheeses. The results will eventually be published in scientific journals, from which food companies are free to use the information.

He has started with lowering the fat even further in part-skim mozzarella. The cheese, which is made in the research center’s labs, is then analyzed with a series of tests, including a computer called a texture profile analyzer. Basically, it’s a computerized taste tester.

After a machine mushes the cheese sample into a blob, the computer analyzes it for seven properties: brittleness, hardness, cohesiveness, springiness, gumminess, chewiness and adhesiveness.

It’s a lot less expensive and easier than hiring taste panels, Tunick said. And besides, he said, “this instrument never gets a cold.”