What else did the grain mills process?
https://books.google.ca/books?id=XMA9gYIj-C4C&lpg=PA768&ots=nJPjb6qaDn&dq=Grain%20Milling%2019th%20century%20london&pg=PA767#v=onepage&q&f=false
Flour
Wheat, Rice, Rye, Oats, Barley, Buckwheat, Maize