From the article: "The main idea was that oak nuts (preferably those from Turkey oaks, Quercus cerris) were to be treated in order to deprive them of tannins,

From the article: "The main idea was that oak nuts (preferably those from Turkey oaks, Quercus cerris) were to be treated in order to deprive them of tannins, and were parboiled in meat broth, or salted water." Looks like boiling/soaking in water will remove tannins