When customers buy Parmesan at their local supermarket, they expect it to be 100 percent cheese.
But an Inside Edition investigation has found that is not always the case.
Freshly grated parmesan tends to clump up and stick together so some manufacturers add cellulose, a harmless additive made from wood pulp, to keep Parmesan cheese from caking.
The FDA says as a general rule there should be no more than two percent cellulose in grated Parmesan cheese but the industry says they can have up to four percent.
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Inside Edition bought 34 samples of Parmesan cheese from major supermarkets, as well as from major restaurant chains like Pizza Hut and Domino's, and sent it to IEH Labs in Seattle, Washington where it was tested for cellulose.
Mansour Samadpour, the president of IEH labs said, "I was very surprised, I did not expect the numbers to be so high."
The results showed that 69 percent of the cheese contained more than the FDA recommends.
A sample from Pizza Hut had 4.9 percent cellulose and one at Domino's came in at 5.4 percent of the filler -- each more than double the FDA guideline. Domino's said the cellulose in its Parmesan cheese falls within the acceptable industry standard.
The label on Stop and Shop's supermarket's brand says "100% grated parmesan cheese with no fillers" - but tests showed it contained 5.8 percent cellulose. When alerted to our findings, the supermarket chain expressed concern and said it has now switched to a new supplier for its grated cheese.
The worst by far was a packet of Colonna brand grated cheese, sold in grocery stores across the country. It had a whopping 21.6 percent cellulose.
"Something fishy is really going on here," food investigator Mitchell Weinberg told Inside Edition. "They are making that much more money by substituting this cheaper filler in place of what should be there."
Colonna Brothers, the maker of the brand with nearly 22 percent cellulose, had no comment.
So, if you want to make sure your Parmesan cheese is 100% cheese, you are going to have to grate it yourself -- or visit upscale restaurants like Patsy's Italian Restaurant or Osteria Morini in New York City, where the Parmesan cheese is freshly grated at your table.