She may say “store-bought is fine”—but not for everything.

Ina Garten has been gracing us with her cooking knowledge for almost 20 years. Her show Barefoot Contessa— named for her 1999 cookbook, as well as her specialty food store—has become a favorite amongst expert and novice chefs alike. On it, she cooks some of her favorite dishes while making mouths water across the country.

While Garten cooks decadent dishes from an array of cuisines with all kinds of ingredients, she has become famous for the line “store-bought is fine.” But, does that mean everything?

In a recent Interview with Time, Garten says the one thing she would never buy in a store is grated Parmesan.

While this may come as a shock, there have been numerous reports claiming that some grated Parmesan containers are filled with cheese fillers—like wood pulp.

So how does this happen? The FDA actually approved for companies to use cellulose (which is derived from wood pulp) in 2-4 percent of products like shredded cheese to help with issues like clumping. But reports indicate many companies are using much more than 4 percent.

As an alternative, your best bet is to buy a chunk of your favorite Parmesan and shred it yourself. It’s not as easy as grabbing a container off the shelf, but it’ll give you (and Garten) a better product and peace of mind. For your next homemade pizza adventure, grab frozen dough and even marinara sauce in a jar, but crank out the grater for some fresh, tasty Parmesan.