What would we do without Parmesan? This flaky cheese is an absolute pantry staple, making appearances in so many of our favorite recipes and topping everything from vegetables to pizza to chili for an extra flavor burst. Nothing really quite captures its distinctive taste— but that hasn’t stopped some brands and companies from trying. As Bloomberg, Buzzfeed and others have reported, there might be another ingredient in our grated Parmesan that’s not only unappetizing, it’s not even food: wood pulp.

Yes, wood pulp, specifically cellulose, the anti-clumping agent it makes. While the agent isn’t toxic, and is commonly added to grated cheeses and other granular foods to prevent clumping, some cheese makers are packing their products so full of it that there’s barely any room left for actual cheese. What’s more, you aren’t even guaranteed that the cheese is Parmesan; some makers substitute cheddar, Swiss, Havarti and mozzarella instead, and simply hope that you don’t notice.

One such brand? Castle Cheese Inc., a Pennsylvania company the U.S. Food and Drug Administration found, during a surprise inspection in 2012, to be perpetuating the fraud. The broader U.S. public is learning the news as the company president faces criminal charges this month, and it’s put us all on alert to pay more attention to where our so-called Parmesan is coming from and which brands are actually real. Here’s our guide:

Parmesan Brands Produced By Castle Cheese, Inc.

These brands were all found by the FDA to contain absolutely NO actual Parmesan, despite their “100%” claims.

• Market Pantry brand 100% grated Parmesan cheese, sold at Target Corp. stores
• Always Save Grated Parmesan Cheese, sold by Associated Wholesale Grocers Inc.
• Best Choice 100% Grated Parmesan Cheese, sold by Associated Wholesale Grocers Inc.

Other Brands To Watch Out For

Bloomberg conducted independent tests on other Parmesans to see if any contained amounts of cellulose higher than the 2 percent to 4 percent recommended by the Center for Dairy Research. Their findings:

• Essential Everyday 100% Grated Parmesan Cheese, from Jewel-Osco, had 8.8 percent
• Great Value 100% Grated Parmesan Cheese, by Wal-Mart Inc., had 7.8 percent
• Kraft had 3.8 percent
• Whole Foods 365 brand had only 0.3 percent, but does not list cellulose as an ingredient

Tips for Getting the Real Deal

Don’t despair! It’s still possible to get find real Parmesan. Just keep the following tips in mind:

• Read the label. If you see cellulose listed, see what the percentage is. If it falls between 2 and 4 percent, it’s likely being used to prevent clumping. Higher than that? The maker might be packing the cheese-making process, so try to avoid it.
• Consider buying blocks of Parmesan from the cheese counter and grating it yourself as you need it. Cellulose and other types of cheese are easier to sneak into grated cheeses, whereas it’s much more difficult – if not impossible – to pass off a block of cheddar, Swiss or wood pulp as Parmesan.
• Check the brands. On one of the lists above? Avoid, especially if it’s on the list of Castle brands. Produced by an Italian or European company – especially one in the Parmigiano Reggiano Consortium – Arthur Schuman Inc., or a trusted local cheesemaker? Enjoy.

We all deserve to know what we’re really eating. Make sure your Parmesan is the real deal, follow our guide, and keep on enjoying that cheesy flavor! Want to learn more about how all this information is coming to light now? Check out Bloomberg’s original article for that and more background on cheese-making.