Library Candy: Fact or Fiction?

City of Thieves is set in Leningrad AKA Piter, which is now St. Petersburg. 
Source: Wikimedia Creative Commons

I'm reading a historical fiction novel called City of Thieves, which is about the German occupation of Russia during World War II. As I was reading along, I came across a reference to "library candy," which, as a future librarian, I couldn't help being intrigued by...

Note: this post contains no spoilers, so read without worry.

In a particular scene, the protagonist and his friend are in a marketplace where some esoteric goods are sold at astronomical prices. In Leningrad during this time, everyone but the most high ranking officers in Russia's Red Army and the Germans occupiers are starving. As a result, goods sold at the marketplace included jars of mud sweetened with honey, a libation called wood alcohol that apparently tasted like fiery dog water, and meat of questionable origin. Then there was this paragraph:

"The boy sold what people called library candy, made from tearing the covers off of books, peeling the binding glue, boiling it down, and reforming it into bars you could wrap in paper. The stuff tasted like wax, but there was protein in the glue, protein kept you alive, and the city's books were disappearing like the pigeons."  

I thought I'd do a little research on this so-called library candy. And I found... nothing. That's right, nothing. I dove into the depths of Google and my alma mater's college library and I found absolutely nothing. I sent out a query to my friends with advanced degrees in history and I'm awaiting their responses. I'll update the post with any new information. 

I don't quite know what to make of this. I know City of Thieves is historical fiction, but library candy just doesn't strike me as the sort of thing one would make up. 

Have you heard about anything similar to library candy in your reading? Tell me in the comments!