I think (don't quote me on this) that the War Raw Materials Dept controlled all the rationing of products due to the allied blockades of their merchant ships, and when the war got really tough on them (around 1917) they began to make 'food substitutes' i.e. coffee beans substituted by acorns, the 'turnip winter' of 1917 in order to provide funding for Ludendorff's plan of doubling munitions output by the next year to secure Germany's victory.
I hope that helped!