NEW YORK — The cheese police are on the case.

Acting on a tip, agents of the U.S. Food and Drug Administration paid a surprise visit to a cheese factory in rural Pennsylvania on a cold November day in 2012.

They found what they were looking for: evidence that Castle Cheese Inc. was doctoring its 100 percent real parmesan with cut-rate substitutes and such fillers as wood pulp and distributing it to some of the country’s biggest grocery chains.

Some grated Parmesan suppliers have been mislabeling products by filling them with too much cellulose, a common anti-clumping agent made from wood pulp, or using cheaper cheddar, instead of real Romano. Someone had to pay. Castle President Michelle Myrter is scheduled to plead guilty this month to criminal charges. She faces up to a year in prison and a $100,000 fine.

How serious is the problem? Bloomberg News had store-bought grated cheese tested for wood-pulp content by an independent laboratory.

Cellulose is a safe additive, and an acceptable level is 2 percent to 4 percent, according to Dean Sommer, a cheese technologist at the Center for Dairy Research in Madison, Wisconsin. Essential Everyday 100% Grated Parmesan Cheese, from Jewel-Osco, was 8.8 percent cellulose, while Wal-Mart Stores Inc.’s Great Value 100% Grated Parmesan Cheese registered 7.8 percent, according to test results. Whole Foods 365 brand didn’t list cellulose as an ingredient on the label, but still tested at 0.3 percent. Kraft had 3.8 percent.

Until recently, there was little incentive to follow labeling rules. Criminal cases are rare. That’s because the FDA, which enforces the country’s food laws, prioritizes health hazards, said John Spink, director of the Food Fraud Initiative at Michigan State University. But civil lawsuits abound. A Jan. 29 complaint accuses McDonald’s Corp. of selling pure mozzarella sticks that contain starch, considered a filler, a claim the company denies.

Source: Bloomberg News